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Additive dominance

answer

A form of incomplete dominance. The heterozygoute is at a midpoint between the homozygotes. Example: the Waxy gene in maize.

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Additive effect (a)

answer

When two genes produce the same effect, but effects are additive if both are present. The difference between two homozygotes.

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Additive variance

answer

A component of genetic variance. Variation passed intect from parent to progeny. Variation in breeding value.

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Adventitious embryony

answer

A type of apomixis. The embryo develops from cells in tissues outside the embryo sac: ovule, nucellus, or integument cells. Most require pseudogamy for seed set. Fertilization occurs, but the nucellar embryo has a faster growth rate than the zygotic embryo. Polyembryonic seeds are produced. The endosperm is generated by fertilization.

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Allele

answer

Different versions of a gene at the same locus.

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Allele frequency

answer

The frequency of a certain allele in a population.

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Allopolyploid

answer

A type of polyploid.

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Anther

answer

The male reproductive organ of flowers. Contains the microsporangia. Each species has a different number of anthers, but the number is constant to each species.

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Antipodal nuclei

answer

Cells in the embryo sac. Three are at the chalazal end of the embryo sac.

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Apomixis

answer

A form of asexual reproduction. Production of seeds from somatic cells of the maternal parent. For some plants, psuedogamy is necessary to induce apomixis. Progeny is genetically identical to the mother. Example: citrus, bluegrass. Four types of apomixis: adventitious embryony, apospory, mitotic diplospory, and meiotic diplospory.

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Apospory

answer

A type of apomixis. An embryo sac develops from cells that differentiated from the nucellus after formation of the megasporocyte. The embryo sac is diploid, so it grows faster than the haploid embryo sacs (not delayed by meiosis). The endosperm is formed by pollination from pseudogamy.

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Approach method

answer

A method of artificial hybridization in wheat. The male spike is placed inside the glycine bag, kept in a drinking straw filled with water.

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Artificial hybridization in Brassicas

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Wind is a more important pollinator than insects. Flowers are indeterminate, and the stigma is receptive 3 days before and 3 days after the flower opens. Pollen can be stored for 4 - 5 weeks.

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Artificial hybridization in carrots

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The flowers are protandrous: pollen is shed before stigmas are receptive. The plants are fastened below the flowers and placed in a cage with flies that pollinate the flowers.

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Artificial hybridization in soybeans

answer

Flowers are typically self-pollinated. Natural cross-pollination is about 1% from insect vectors. The flower has 5 petals: the standard, two wing petals, and two keel petals.

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Artificial hybridization in wheat

answer

Two methods: Go-Go method and Approach method.

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Asexual reproduction

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Vegetative reproducction
Reproduction through plant parts other than the seed. Includes: bulb, corm, tuber, rhizome, stolon, micropropagation, and somatic embryogenesis. Apomixis, parthenogenesis, and artificial means such as cutting, grafting, layering, and tissue culture are also forms of asexual reproduction.

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Autopolyploid

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A type of polyploid.

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Awned

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There are long spikes, awns, on the lema of wheat or barley.

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Axial cell

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Apical cell
One of the cells formed in the first division of the zygote. It divides to form the embryo.

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Basal cell

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One of the cells formed in the first division of the zygote. In dicots it divides to form the suspensor. In monocots it does not divide, and forms the terminal cell of the suspensor.

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Basmati rice

answer

Rice with a good flavour, controlled by a genet. But no-one created the gene! Can you patent it?

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Binucleate stage

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The first stage in microgametogenesis. The microspore has cytoplasmic division, producing a generative cell and a tube cell. Most pollen is released in this stage.

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Both self- and cross-pollination

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Some species have both self- and cross-pollination, with about 50% of each. Example: cotton, pigeon pea.

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Brassica campestris

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Highly self-incompatible. Self-pollinated seed is produced with difficulty.

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Brassica hirta

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Highly self-incompatible. Self-pollinated seed is produced with difficulty.

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Brassica jucea

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Self-fertile. 80% of seed is from self-pollination. This number is smaller when insect pollinators are abundant.

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Brassica napus

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Self-fertile. 80% of seed is from self-pollination. This number is smaller when insect pollinators are abundant.

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Breeding Field Crops

answer

A book by John Pullman.

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Breeding Value

answer

The value of an individual as judged by the mean value of the progeny.

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Broad sense heritability

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Genotypic variation / Phenotypic variation
An estimate of heritability. Measures the proportion of total variance that is genetic. Found using selfed progeny and progeny-parent regression heritability estimates.

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Bulb

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A form of asexual reproduction. A large bud with a small stem at the lower end; buds in the axils of fleshy, scale-like leaves permit the bulb to be divided for asexual reproduction. Example: onion, garlic, tulips, lilies.

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Cellular endosperm development

answer

The endosperm divides normally with cytokinesis; there is no free nuclear stage.

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Centre of origin

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The origin of a cultivated species. Has wild species in addition to landraces. High level of genetic diversity.

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Chalazal end

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The end of the embryo sac opposite from the micropylar end. The antipodal cells are on this end.

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Chasmogamy

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A device that promotes out-crossing. Flowers are open at anthesis.

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Chi-square (?²)

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A test of goodness of fit. The smaller the value, the more likely the hypothesis is correct.

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Chiasma

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Plural: chiasmata
The point where two homologous, non-sister chromatids exchange genetic material during crossing over.

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Chloroplasts

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One of the places in the plant cell where DNA is kept. Chloroplast DNA is inherited maternally in most angiosperms, from both parents in some angiosperms, and paternally in a few angiosperms and most gymnosperms.

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Chromosome

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A condensed strand of DNA.

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Cleistogamy

answer

A device that promotes self-pollination. Flowers are closed at anthesis. Example: soybean, barley, wheat, oats.

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Colchicine

answer

A chemical that doubles the number of chromosomes.

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Complementary action

answer

When two non-allelic genes are required to produce a single effect.

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Complementation

answer

Duplicate recessive
A type of epistasis
aa is epistatic to B and b
bb is epistatic to A and a
Produces 9:7 ratios

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Complete dominance

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When the heterozygote shows the same phenotype as one of the homozygotes.

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Complete flower

answer

Has all four floral organs: sepals, petals, stamens, and pistils.

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Corm

answer

A form of asexual reproduction. Resembles a bulb in size and form, but has different internal structure. Leaves are thin and small. Roots develop from the lower surface of the stem. Example: crocus, gladiolus.

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Cross-pollinated species

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Allogamy
Have devices to promote outcrossing: chasmogamy, dioecious flowers, monoecious flowers, pin and thrum flowers, protandry, protogyny, protective film over the stigma, self-incompatibility, and male sterility. Often perennial. May also have asexual modes of reproduction. Individuals are heterozygous at many loci. Reduced performance when self-pollinated; inbreeding depression due to deleterious alleles in the population. Wild populations are heterogenous. Cultivated varieties are either heterogeneous or homogenous.
Natural self-pollination rates: 0% - 5%
Examples: corn, alfalfa, carrot, onion, rye, sunflower

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Crossing over

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A source of diversity from meiosis. Formation of a chasma and exchange of genetic material between chromosomes. Results in recombinant chromosomes. Genotype frequencies are unusual.

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Cytoplasmic DNA

answer

DNA in the mitochondria or chloroplast. Circular DNA, distinct from nuclear DNA. Usually inherited uniparentally.

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Cytoplasmic male sterility

answer

Male sterility controlled by the cytplasm, with many influences from nuclear genes, inhibiting normal development of anthers.

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Davis

answer

A soybean variety resistant to Frogeye leaf spot.

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Dioecious

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A device that promotes out-crossing in imperfect flowers. Male and female reproductive parts are on separate plants.
Example: date plum, papaya, asparagus, hemp, hops

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Diploid

answer

Two chromosome sets, one from each parent. Chromosomes are in homologous pairs. May be homozygous or heterzygous.

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DNA

answer

A long, double-helix molecule with 2 complementary strands with opposite polarity.

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Dominance

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The dominance of alleles determines the phenotype of an organism.

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Dominance variance

answer

Genetic variance that results from allelic interactions within loci.

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Dominant epistasis

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A type of epistasis.
A is epsitatic to B and b
Produces a 12:3:1 ratio

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Double fertilization

answer

Unique to angiosperms. The egg cell is fertilized by a sperm cell, resulting in a diploid zygote. The polar nuclei are ferilized by the second sperm, resulting in the endosperm.

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Duplicate action

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When either of two genes produce a similar effect.

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Duplication

answer

A type of epistasis
A is epistatic to B and b
B is epistatic to A and b
Prouces a 15:1 ratio

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Durum wheat

answer

Triticum turgidum
2n = 4x = 28 AABB
One of the parents of triticale.

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Egg

answer

A cell in the embryo sac. At the micropylar end. It is fertilized by a sperm cell to produce the zygote.

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Embryo

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A diploid component of a seed. Develops from the axial cell of the zygote. In dicots it has four stages of development: globular, heart, late heart, and torpedo stage.

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Embryo sac

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Megagametophyte
Formed from the megapore in megagametogenesis. IT consists of seven cells and eight haploid nuclei: one egg, two polar nuclei (in one cell), two synergids, and three antipodal nuclei. Some species have more or less than the usual eight nuclei. It is surrounded by integuments, with the micropyle at one end. The micropylar end is near the micropyle, and the chalazal end is opposite from teh micropyle.

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Endosperm

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Forms from fusion of a sperm and the polar nuclei. Usually triploid, but can be 2n through to 15n. It draws nutrients from adjacent tissues. It either has nuclear development or cellular development. In monocots and endospermic dicots (such as castor beans0, the endosperm is generally no used until germination). In non-endospermic dicots, the endosperm reserve is depleted and reorganized into bulky, nutrient-rich cotyledons during seed development.

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Epistasis

answer

Expression of a gene at one locus affects the phenotypic expression at another locus. Incldues recessive epistasis, dominant epistasis, suppression, complementation, and duplication.

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Epistatic variance

answer

Genetic variation created by interactions between loic. Interactions are not passed intact from parent to progeny. Difficult to select for.

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Environmental variance

answer

Variance due to the environment. Due to the inability to treat all genes equally.

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Essentials of Plant Breeding

answer

A book by Rex Bernardo.

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Frogeye Leaf Spot (FLS)

answer

A disease in soybeans caused by a fungus in hot humid soybean regions such as Brazil, China, Nigeria, and southern US. Causes yield losses 10 - 50%. Resistance is controlled by one or two genes. Susceptible plants have large, spreading, fertile lesions. Resistatn plants have no lesions, and small sterile flecks.

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Full-sib progeny

answer

A type of progeny-parent regression
b = narrow-sense heritability

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Gametophytic self-incompatibility

answer

Self-incompatibility where the genotype of the haploid gametes determines the compatibility reaction. If the allele in the pollen matches one in the female plant, then fertilization fails.

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Gene

answer

A stretch of DNA that transcribes a functional RNA or enables transcription of a protein.

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Gene bank

answer

A source of genetic diversity. Accessions are categorized by geographical source and phenotypic traits. Canada's main gene bank used to be in Ottawa, but was moved to Saskatoon in 1988.

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Generative cell

answer

One of the cells formed in the binucleate stage of microgametogenesis. It divides to form two sperm cells in the trinucleate stage.

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Genetic advance

answer

The change in mean of a population from one generation cycle of selection.

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Genetic male sterility

answer

Male sterility manifested through action of nuclear genes, inhibiting normal development of anthers.

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Genetic variance

answer

The variation due to genetic differences among plants. Consists of additive, dominance, and epistatic variance.

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Genetics

answer

The study of genes through their variation, or the study of inheritance.

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Genome

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The entire genetic information of an organism.

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Genotype by environment (G x E) variance

answer

Variance due to genotypes responding differently to different environments. Reduces the association between genotypic and phenotype values. May cause selections from one environment to perform poorly in another environment. Minimized by using many environments and many replications.

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Genotype frequency

answer

The frequency of a certain genotype in a population.

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Germplasm Resource Information Network (GRIN)

answer

A source of information on accessions in gene banks. You can order accessions for free from the Canada gene bank.

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Globular stage

answer

The first stage of embryo development. The embryo is sphere shaped.

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Go-Go method

answer

A method of artificial hybridization in wheat. The male spike is shaken inside the opening bag containing the female spike. The bag is then resealed.

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Half-sib progeny

answer

A type of progeny-parent regression.
2b = narrow-sense heritability

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Hardy-Weinberg Equilibrium

answer

Described by G.H. Hardy and W. Weinberg in 1908. Frequencies of alleles and genotypes stay constant if the population is large, randomly mating, absent of mutations, absent of selection, absent of migration.

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Heart stage

answer

The second stage of embryo development. Three major regions of mitotic activity: two on either side of the top of the embryo, and one near the suspensor. These develop into the cotyledons and radicle.

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Heritability (h²)

answer

The proportion of the phenotypic variation that is due to genotype. Estimates of heritability can be used to predict selection gain. Includes broad sense and narrow sense estimates.

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Heterozygous

answer

Having different alleles on two homologous chromosomes.

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Hooded

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The lema of barley or wheat has a "hood" over it.

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Homologous chromosomes

answer

Chromosomes in a diploid organism which carry the same gene loci. May be homozygous or heterozygous.

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Homozygous

answer

Having the same allele on both homologous chromosomes.

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High leaf starch (hls)

answer

A mutation in alfalfa causing increased activity of invertase, leading to starch build-up in the leaf. It is transmitted paternally more than it is transmitted maternally; this established that in Medicago species plastids are inherited paternally. It is studied using Restriction Fragment Length Polymorphism.

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Hybrid vigour

answer

When the heterozygote is better than either homozygote.

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Incomplete dominance

answer

Includes additive, partial, and over-dominance.

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Incomplete flower

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Lacks one or more floral organs: sepals, petals, stamens, or pistils.

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Independent assortment of chromosomes

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A source of diversity from meiosis. Different chromosomes are independently separated from one another during gamete formation.

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Inhibiting action

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When one gene inhibits the effect of another gene at another locus.

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Integuments

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Surround the embryo sac. Has a small opening at one end, the micropyle. After fertilization, develops into the testa.

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Invertase

answer

A protein that exports sucrose from the cell. In high leaf starch alfalfa mutants it has increased activity, resulting in starch build-up in the leaf.

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Keel petal

answer

A petal in soybean flowers. There are two keel petals.

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Landrace

answer

A cultivated form that evolved from a wild population, which is endemic to an area with origins going back 100s of years, well adapted to the environment, a mixture of types.

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Late heart stage

answer

The third stage of embryo development. Elongation of regions of mitotic activity, defining cotyledons.

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Law of Independent Assortment

answer

Alleles at a locus segregate independently from alleles at another locus, when gametes are formed.

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Law Segregation

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Alleles of a gene separate randomly when gametes are formed.

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Lee

answer

A soybean vareity susceptible to most races of Frogeye leaf spot.

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Linkage

answer

Genes are on the same chromosome. Produces unusual segregation ratios.

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Locus

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The location of a gene on a chromosome.

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Male sterility

answer

A device that promotes out-crossing. Includes genetic and cytoplasmic male sterility.

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Masking action

answer

When one gene hides the effect of another gene at another locus, when both are present.

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Mean (?)

answer

A measure of central tendency, used when studying quantitative traits in populations.

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Megagametogenesis

answer

The megaspore undergoes division to form seven cells and eight nuclei that form the embryo sac.

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Megaspore

answer

A haploid cell formed via meiosis of the megasporocyte. Arranged in a tetrad cluster or linear arrangement. Four are produced per megasporocyte, but three degenerate.

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Megasporocyte

answer

Megaspore mother cell
Undergoes meiosis to form four megasporogenesis to form four megaspores.

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Megasporogenesis

answer

The megasporocyte undergoes meiosis to form four megaspores within the nucellus.

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Meiosis

answer

Diploid cells divide to produce haploid cells. It produces diversity from independent assortment of chromosomes, and from crossing-over. Halves the number of chromosomes during production of sex cells. There is independent segregation of genes.

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Meiotic diplospory

answer

A type of apomixis. The megasporocyte differentiates from the nucellus, but has a failure in meiosis I, resulting in a diploid megaspore. Development of an embryo from parthenogenesis; pollination is not required.

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Microgametogenesis

answer

Development of pollen grains from microspores. Includes the binucleate and trinucleate stages.

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Micropropagation

answer

A form of asexual reproduction.

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Micropylar end

answer

The end of the embryo sac near the micropyle. The egg and synergids are on this side.

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Micropyle

answer

A small hole in the integuments on the micropylar end of the embryo sac. The pollen tube enters through this opening.

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Microsporangia

answer

Pollen sacs
Microsporogenesis occurs here.

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Microspore

answer

A haploid cell formed via meiosis of the microsporocyte in microsporogenesis.

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Microsporocyte

answer

Microspore mother cell
Undergoes meiosis in microsporogenesis, forming 4 microspores.

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Microsporogenesis

answer

The microsporocyte undergoes mieosis to form 4 microspores within the microsporangia of the anther.

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Mitochondria

answer

One of the places in the plant cell where DNA is kept. Mitochondrial DNA is inherited maternally.

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Mitosis

answer

Diploid cells divide to produce diploid cells. Chromosomes are partitioned into daughter cells during somatic division.

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Mitotic diplospory

answer

A type of apomixis. The megasporocyte is inhibited from entering meiosis. The embryo sac is diploid, but is identical in structure to the haploid embryo sac. The embryo is formed from parthenogenesis; pollination is not necessary. The endosperm is also produced by parthenogenesis, but in some cases pseudogamy is required form the endosperm.

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Modifying action

answer

When one gene inhibits the effect of another gene at another locus.

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Monoecious

answer

A device that promotes out-crossing in imperfect flowers. Male and female reproductive parts are on separate flowers on the same plant. Example: maize

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Mutation

answer

Genes or chromosomes changing from one allele to another.

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Narrow sense heritability

answer

An estimate of heritability. The proportion of variance that is additive. The proportion which can be selected for. Found using full-sib and half-sib progeny-parent regression method.

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Nucellus

answer

Megasporogenesis occurs here. Devlops into the perisperm in some species.

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Nuclear endosperm development

answer

The endosperm undergoes several free nuclear divisions prior to cell wall formation.

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Nucleus

answer

One of the places in the plant cell where DNA is kept. Nuclear DNA is inherited maternally and paternally.

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Over-dominance

answer

A type of incomplete dominance. The homozygote is greater than either heterozygote.

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Parthenogenesis

answer

A form of asexual reproduction. An embryo develops without fertilization, resulting in haploid progeny. No pollination is necessary.

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Partial dominance

answer

A type of incomplete dominance. The homozygote is between both homozygoutes, but is not at the midpoint.

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Peking

answer

A soybean variety that is resistant to Frogeye leaf spot.

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Perisperm

answer

Develops from the nucellus in some species. Assumes the role of the endosperm. Diploid, derived from the mother plant. Example: coffee.

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Phenotype

answer

Determined by the dominance of alleles in an organism.

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Phenotypic variance

answer

Genetic variance + Environmental variance + G x E interaction

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PI 51461

answer

A soybean variety resistant to Frogeye leaf spot.

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Pin and thrum

answer

A device that promotes out-crossing in imperfect flowers. Example: primula.

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Plant DNA

answer

Found in the nucleus, mitochondria, and chloroplasts.

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Pleiotropic genes

answer

When a single gene may have more than one effect.

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Polar nuclei

answer

A component of the embryo sac. Two nuclei in one cell. Near the centre of the embryo sac. It is fertilzied by a sperm cell to form the endosperm.

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Pollen grain

answer

Microgametophyte
Formed from microspores in microgametogenesis.

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Pollination

answer

Pollen grains are transferred into the stigma by a variety of vectors: insects, animals, wind. Many species enter trinucleate stage at this point, producing two sperm cells. The pollen grain absorbs water and nutrients from the stigma surface, and the pollen tube emerges and grows through the stigma and style to the embryo sac, and enters the ovule through the micropyle. It penetrates a synergid, and deposits sperm cells.

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Polyembronic seeds

answer

Seeds with more than one embryo. Created in adventitious embryony; there are a number of nucellar embryos in different stages, with or without a zygotic embryo.

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Polyploid

answer

Originate as autopolyploids or allopolyploids.

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Population

answer

A group of interbreeding individuals that exist together in time and space. Distribution is measure with mean and variance.

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Pre-breeding

answer

Creates genetics that you cannot get directly. There are seveal processes before getting the final product. Breeding with landraces or wild species transfers unwanted traits, which are removed in pre-breeding.

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Princess

answer

A variety of dry bean Johannsen used in his experiments. Continuous breeding had no result because it was a pure-line.

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Progeny-parent regression

answer

Calculating the regression coefficient of a line of parental vs. progeny phenotype. A higher number means a higher heritability. There are three types: selfed progeny, full-sib progeny, and half-sib progeny.

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Progeny testing

answer

Learning the genotype of a plant by growing and observing characteristics of its progeny.

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Protandry

answer

A device that promotes out-crossing. Stamens develop before pistils.

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Protective film over the stigma

answer

A device that promotes out-crossing in perfect flowers.

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Protein

answer

The product of genes. Transcribed based on the sequence of RNA strands.

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Protogyny

answer

A device that promotes out-crossing. Stamens develop after pistils.

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Pseudogamy

answer

When pollination and pollen tube development is necessary to induce apomixis.

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Pure line

answer

The progeny of a single plant, self-fertilized over many generations. All plants are homozygous and homogenous.

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Pure Line Theory

answer

Postulated by Wilhelm Johannsen in 1903. Continuous inbreeding leads to homozygosity. Variation within pure lines is caused by the environment only. Selection within a pure line is ineffective; all plants are genetically identical.

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Qualitative trait

answer

Controlled by a few loci. Expression is not influenced by the environment. Phenotypes can be divided into discrete classes. Studied by analyzing the phenotypic ratios and inheritance patterns. Can show complete or incomplete dominance, and epistasis. Example: awned vs. hooded wheat and barley.

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Quantitative trait

answer

Controlled by many loci. Expression is influenced by the environment. Phenotypes overlap and/or display continuous variation. Genotype cannot be determined from phenotype. Studied using measures of central tendency in populations. When environmental variation is eliminated, it can appear qualitative; Mendelian segregation patterns are followed. Example: yield in wheat.

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Recessive epistasis

answer

A type of epistasis
aa is epistatic to B
Produces a 9:3:4 ratio

question

Reciprocal cross effect

answer

Sometimes a different genotype is produced from different combinations of the sexes of the parents. Example: A female x B male vs. B female x A male, produce different phenotypes in the offspring. Indicates that genes are on mitochondrial or chloroplast DNA. Studied with Restriction Fragment Length Polymorphism. Example: high leaf starch mutation.

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Recombinant

answer

Gene trait combinations that are a result of crossing-over.

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Regression coefficient (b)

answer

The slope of the line made in a progeny-parent regression method for estimating heritability.

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Response to selection (R)

answer

ckh²Ve
k is standardized selection differential
c is the parental control factor
To improve R, you can increase selection intensity, variability, or heritability (reduce errors in measurement of phenotype).

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Restriction Fragment Length Polymorphism (RFLP)

answer

A marker used to follow transmission of plastids. Used to study high leaf starch mutation in alfalfa.

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Rhizome

answer

A form of asexual reproduction. An underground horizontal stem that shoots and roots at nodes. It can be mistaken for a root when it grows underground. Example: bamboo, sugarcane, banana.

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RNA

answer

A single-stranded molecule. Translated from genes. Can enable transcription of a protein.

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Rye

answer

2n = 2x = 14 RR
One of the parents of triticale.

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Seedless watermelon

answer

Triploid watermelon are sterile and produce no seeds. A diloid watermelon is treated with colchicine to produce a tetraploid watermelon, which is then backcrossed with diploid watermelon to create triploid progeny.

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Selection differential (S)

answer

The mean phenotypic value of all the individuals selected as a derivation from the population mean.

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Selection intensity

answer

The proportion of the population which the breeder discards.

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Self-incompatibility (SI)

answer

A device that promotes out-crossing. The inability of a plant to produce a zygote by self-pollination. Several mechanisms: pollen fails to germinate on the stigma, pollen tube is inhibited, pollen tube is insufficient length or strength, or the male gamete fails to unite with the egg cell. Can be gemetophytic or sporophytic.

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Self-pollinating species

answer

Autogamy
Have devices to promote self-pollination: cleistogamy, staminal sheaths. Often annual species. Individuals are homozygous at many loci; there is no inbreeding depression. Wild populations are heterogeneous. Cultivated varieties are homogeneous - all individuals have the same genotype. Inheritance follows the Pure Line Theory.
Natural cross-pollination rates: 0% - 5%
Examples: barley, common bean, chickpea

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Selfed progeny

answer

A type of progeny-parent regression
b = broad-sense heritability

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Sexual reproduction

answer

Fusion of male and female gametes, regardless of whether they originate from one or more flowers or plants. Includes cross- and self-pollinating species. Each group has devices to promote their mode of reproduction.

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Sperm cell

answer

Two cells that arise from the generative cell of a pollen grain in trinucleate stage. One fertilizes the egg cell, forming the zygote. The other fertilizes the polar nuclei, forming the endosperm.

question

Sporophytic self-incompatibility

answer

Self-incompatibility where the genotype of the male parent determines the compatibility reaction. If either allele in the male parent matches one in the female parent, fertilzation fails, regardless of the genotype of the pollen grain. The genotype of the male parent is marked on the exine.

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Somatic embryogenesis

answer

A form of asexual reproduction. An embryo forms, and balanced hormones are used to produce a plant. Fertilization does not occur.

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Staminal sheath

answer

A device that promotes self-pollination. The stamens are joined, surrounding the pistil. The pistil grows through the pollen, causing self-pollination. Example: cotton.

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Standard petal

answer

A petal of a soybean flower. There is one standard petal.

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Stigma

answer

The floral organ which receives pollen.

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Stolon

answer

Runners
A form of asexual reproduction. An above-ground horizontal stem. Example: strawberry, creeping bentgrass, Bermuda grass.

question

Suppression

answer

A type of epistasis.
A is epistatic to B and b
bb is espistatic to A and a
Produces a 13:3:0 ratio

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Suspensor

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In dicots it is formed from the basal cell. In monocots it is formed from the axial cell, but its terminal cell is formed from the basal cell. Synthesizes growth factors and transports nutrients to the embryo. Can be unicellular, multicellular, large, small, filamentous, columnar, spherical, or irregular in shape.

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Synergids

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Cells in the embryo sac. There are two at the micropylar end. The pollen tube penetrates a synergid and disintigrates after fertilization.

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Terminal cell

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Formed from the basal cell in monocots. Becomes part of the suspensor, which is derived from the axial cell.

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Test cross

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Crossing a plant with a homozygous recessive individual to identify its genotype.

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Testa

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Seed coat
Develop from integuments. Diploid, derived from the mother plant.

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Torpedo stage

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The fourthe stage of embryo development. Further elongation results in a bend in the region of the hypocotyl.

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Transcription

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The formation of a protein based on the sequence of an RNA strand.

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Transgressive segregation

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When progeny fall outside of the range of the parents.

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Trinucleate stage

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The second stage in microgametogenesis. In most species it occurs when the pollen grain lands on the stigma. In others, it occurs before pollen is released. The generative cell undergoes division, forming two sperm cells.

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Triticale

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The first man-made crop. A cross between durum wheat (4n = 28 = AABB) and rye (2n = 12 = RR), creating a sterile 3n = 21 = ABR individual. Colchicine was used to double the chromosomes, producing 6n = 42 = AABBRR triticale.

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Tube cell

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Vegetative cell
One of the cells formed in the binucleate stage of microgametogenesis. Helps the sperm cells reach the egg.

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Tuber

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A form of asexual reproduction. A swollen, modified stem that acts as an underground storage organ. Example: potato, Jerusalem artichoke, yam.

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Variance (?²)

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A measure of distribution. Used in studying quantitative traits in populations.

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Waxy

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A gene in maize that shows additive dominance.

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Wheat

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Has genes transgressed in from GP2 and GP3. It has 21 pairs of chromosomes.

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Wilhelm Johannsen

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Postulated the Pure Line Theory in 1903. Used Princess dry beans in his experiments.

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Wing petal

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A petal in soybean flowers. There are two wing petals.

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Zygote

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A diploid cell formed from fusion of the egg and a sperm. It develops into the embryo of the seed. The first division in the zygote forms the axial and basal cells.

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