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Alternation of generations

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Reproductive cycles in which a haploid phase alternates with a diploid phase. Alternation of gametophytic and sporophytic generations in a life cycle. Gametophytes produce spores that fertilize with each other to form a diploid zygote that becomes the sporophyte. The sporophyte then undergoes meiosis to produce gametophytes.

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Androgenesis

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Apomixis where an embryo develops from sperm nucleus of pollen after it enters the embryo sac.

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Angiosperm

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The most dominant form of plant on Earth. There are 250,000 species. Fertilization by pollen and pollen tube; water is not required for fertilization, as sperm are non-motile. Cross-pollination can occur over distances by wind or insects. Heterosporous. The endosperm provides embryo nutrition. Dormant seeds form in a developed ovary (fruit). Seed dormancy allows for seed dispersal mechanisms and development of a seed bank. Seeds germinate when conditions are right. Seeds can survive for years, and can be transported to colonize new areas.
1. Microspore mother cells form in microsporangia, and undergo meiosis to produce four microspores each. The first mitotic division gives rise to vegetative and generative cells, divided by a thin wall. The generative cell divides to produce two sperm cells, before or after pollination.
2. Megaspore mother cells form in megasporangia, and undergo meiosis to produce four megaspores each, three of which die. The surviving megaspore undergoes three rounds of mitosis, producing eight nuclei. Four nuclei move to each pole, then one from each end moves to the centre, and thin cell walls form around the remaining six, forming the embryo sac.
3. Upon pollination, a pollen tube forms from the vegetative cell, and grows through the style to the ovule, through the micropyle, and into the embryo sac where it discharges the two sperm cells into a synergid.
4. Double fertilization: one sperm fuses with the egg to form a diploid zygote, and one sperm fuses with the central cell's two polar nuclei to form a triploid endosperm. Synergids and antipodals disintegrate.
5. The embryo and endosperm both divide mitotically and, with parts of the ovule, develop into the seed.

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Antheridium

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Multicellular male gametangium of plants other than seed plants.

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Antipodal cells

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Three cells of the mature embryo sac, located at the chalazal end.

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Apomixis

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Asexual reproduction with formation of a seed. A seed is produced from an unfertilized egg, or a somatic cell of the maternal plant. Found in obligate and facultative apomicts. Depends on the pollen parent, temperature, photoperiod, salts, or nutritional levels. It is a dominant trait, whether one or a few genes. If corn could be made to have apomixis, there could be self-perpetuating hybrids. Includes apospory, diplospory, sporophytic apomixis, parthenogenesis, androgenesis, semigamy, and pseudogamy.

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Apospory

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Gametophytic apomixis
Apomixis where the megaspore mother cell divides metiotically, but all resulting cells die instead of just three. A somatic cell of the ovule then divides mitotically to form a diploid embryo sac that becomes the embryo. The endosperm may develop with or without fertilization from pollen, depending on the species, but the latter is rare. Common in Kentucky bluegrass.

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Archegonium

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The female sex organ of spike moss and bryophytes, which develops on the megagametophyte. A multicellular structure that contains eggs.

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Asexual reproduction

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A new plant forms from somatic cells without union of gametes. Includes vegetative reproduction and apomixis. The progeny has identical genotype to the parent. It is beneficial if there is a very successful genome, which is heterozygous. Plants may not even need pollinators.

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Barley

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Fertilization takes one hour.

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Bluegrass

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Apospory is common in Kentucky bluegrass. Sexual and asexual reproduction occurs on the same plant, or some percentage of plants are sexual.

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Brassicaceae

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A family of plants which has sporophytic self-incompatibility. The S locus encodes two genes: SRK (female determinant), which codes for a transmembrane protein in stigmatic papillae, and SP11 (SRC) (male determinant). When a pollen grain lands on a stigma, if its SP11 haplotype matches with the SRK haplotype of the stigma, the proteins interact and activate kinase function of SRK, leading to pollen rejection. There is no interaction between components with different haplotypes.

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Cabbage

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Fertilization takes 5 days.

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Central cell

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The large cell of the embryo sac which contains two polar nuclei.

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Chalaza

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The region of the ovule or seed where the funiculus unites with the integuments and nucellus, opposite from the micropyle.

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Chasmogamy

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The stigma is receptive and pollen sheds after the flower opens. Results in mixed self- and cross-pollination, depending on flower morphology and insect activity.

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Cleistogamy

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The stigma is receptive and pollen sheds inside a closed flower. A timing mechanism that results in self-pollination. Includes soybean.

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Codominance

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Heterozygotes have both traits at once; neither allele is masked.

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Codominant sporophytic self-incompatibility

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Both haplotypes present in the genotype contribute to SI response. The pollen can affect fertilization if male and female parents have no haplotypes in common at the S locus. A diallelic cross produces two cases where seed is produced, and five cases where it is not.

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Corn

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Fertilization takes 50 hours.

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Cross-pollination

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Union of gametes from different plants. Can be promoted by separate male and female flower organs in monoecious or dioecious plants. It is favoured by protandry, protogyny, and self-incompatibility. Wild populations are heterogeneous. Individual plants are heterozygous, and progeny are heterogeneous. Deleterious alleles are hidden. There may be inbreeding depression. Favourable alleles spread, and new genetic combinations for natural selection occur.

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Dandelion

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A triploid obligate apomict.

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Dicot

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Has two cotyledons. In some species, including beans, the embryo consumes the endosperm before seed maturation, and cotyledons become the energy source for the germinating embryo. In castor beans, the endosperm stays as part of the mature seed.

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Dioecious

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Male and female imperfect flowers form on separate plants. Includes asparagus, hops, and holly.

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Diplospory

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Gametophytic apomixis
Apomixis where the megaspore mother cell does not undergo meiosis, but proceeds directly to mitosis to produce an embryo sac within a diploid egg cell. The diploid egg divides mitotically to produce a diploid embryo. The endosperm may develop with or without fertilization from pollen, depending on species, but the latter is rare. Common in perennial grasses.

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Dominant sporophytic self-incompatibility

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Dominant haplotypes contribute to the SI response. The pollen can affect fertilization if the female does not have the higher order of haplotypes of the male parent at the S locus. A diallelic cross produces three cases where seed is produced, and six cases where it is not.

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Double fertilization

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Fusion of the egg and sperm results in a diploid zygote, and simultaneous fusion of the second sperm with polar nuclei results in a triploid primary endosperm.

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Facultative apomict

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When most seeds form from apomixis, but sexual reproduction does occur regularly. A fixed genetic combination can colonize an ecological niche, but retain the ability to evolve.

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Embryo sac

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The female gametophyte of angiosperms. It has seven cells and eight nuclei. There are three antipodal cells, two synergids, one egg, and one central cell, which contains two nuclei. The egg and synergids are at the micropylar end, and the antipodal cells remain at the chalazal end.

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Endosperm

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Triploid tissue containing stored food that develops from the union of a sperm cell and the polar nuclei of the central cell. Found only in angiosperms. Digested by the growing sporophyte either before or after maturation of the seed.

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Flower morphology

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Affects pollination biology. Predicts degree of self- vs. cross-pollination. If the anther is above the stigma, and/or enclosed in another cone, or if the flower is small, not showy, with no scent or nectar, it favours self-pollination. If the stigma is above the anther, or if the flower is showy, scented, with nectar, or wind-borne pollen, it favours cross-pollination.

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Funiculus

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The stalk of the ovule.

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Gametangium

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Any cell or organ in which gametes are formed.

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Gamete

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The mature functional haploid reproductive cell. Its nucleus fuses with another gamete of the oppsote sex, resulting in a diploid zygote.

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Gametophyte

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In plants with alternation of generations, the haploid gamete-producing phase.

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Gametophytic self-incompatibility

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Incompatibility is determined by the genotype of the pollen. The site of action is the style. The male gamete is able to affect fertilization if the haplotype it possesses at the S locus differs from both allels in the pistil. Found in the Solanaceae and Papaveraceae families. May have self-recognition or non-self recognition. A diallelic cross produces four cases where seed is produced, and five cases where it is not.

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Generative cell

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One of the cells of the pollen grain. It is smaller than the vegetative cell, and it undergoes mitosis before or after pollination to form two sperm cells.

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Guelph Millennium

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A variety of asparagus which is suited to Ontario, developed by Prof. Wolyn. 98% of Ontario asparagus is this variety.

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Gymnosperm

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A seed plant with seeds not enclosed in an ovary.

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Haplotype

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A group of alleles of different genes on a single chromosome that are closely linked such that they are inherited as a single unit. There are mechanisms which prevent genetic crossover events within the haplotype.

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Heterosporous

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Having different types of spores: mega- and microspores.

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Homosporous

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Having only one type of spore. Similar spores can fertilize each other.

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Honey bee

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Apis mellifera
They are attracted to soybean flowers, and will cross-pollinate soybeans. They usually work their way down rows of plants while pollinating, occasionally jumping rows. On cool days they will not emerge from their nest.

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Inbreding depression

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Loss of vigour from self-pollination. Cross-pollinating species accumulate deleterious recessive alleles which rarely become homozygous in a population due to outgcrossing. With self-pollination, homozygosity is achieved, exposing deleterious phenotypes. It is absent from self-pollinators because deleterious alleles are lost from the population. To determine its level, self-pollinate and look for loss of vigour.

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Integument

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The outermost layer or layers of tissues enveloping the nucellus of the ovule. Develops into the seed coat.

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Least significant difference (LSD)

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A statistical method of separating means. Means with the same letter cannot be considered different.

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Male sterility

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No functional pollen is produced without affecting female fertility. Plants can set seed if cross-pollinated, with nuclear or cytoplasmic genes.

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Maternal inheritance

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Chloroplast and mitochondria are inherited from the egg in most cases. Paternal chloroplast inheritance is observed in certain species.

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Maturity group

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Groupings of soybean varieties based on when flowering occurs. Flowering is triggered by heat effects and photoperiod.

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Megagametophyte

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The female gametophyte. In angiosperms, it is the embryo sac.

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Megasporangium

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The structure in which megaspore mother cells and megaspores are produced.

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Megaspore

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A haploid spore that develops into a female gametophyte.

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Megaspore mother cell

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Megasporocyte
A diploid cell in which mieosis occurs, forming four megaspores.

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Micropyle

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In the ovules of seed plants, the opening in the integuments through which pollen usually enters. Opposite from the chalaza.

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Microsporangium

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The structure in which microspore mother cells and microspores are produced.

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Microspore

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A haploid spore that develops into a male gametophyte.

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Microspore mother cell

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Microsporocyte
A diploid cell in which meiosis will occur, forming four microspores.

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Mixed pollination

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A plant which has a mixture of self- and cross-pollination.

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Monocot

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Has one cotyledon. The endosperm is the energy source for the germinating embryo. Includes corn.

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Monoecious

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Separate imperfect male and female flowers on the same plant. Includes con, cucumber, squash, and pumpkin.

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Nicotine

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One plant has nectar laced with nicotine as well as benzoacetone, which is attractive to its moth pollinators. The nicotine encourages the pollinators to spend less time at the flower, and to pollinate more flowers. It also deters insects from eating the flowers.

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Nucellus

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Tissues composing the chief part of a young ovule, in which the embryo sac develops. Equivalent to megasporangium.

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Obligate apomict

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When all seeds form from apomixis except for rare plants capable fo sexual reproduction.

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Ovule

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A structure in seed plants containing the female gametophyte with egg cell, all being surrounded by the nucellus and one or two integuments. Mature when the ovule becomes the seed.

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Papaveraceae

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A family of plants which has self-recognition gametophytic self-incompatibility. The S locus encodes two genes: PrsS (female determinate), and PrpS (male determinant). PrpS is a receptor on the pollen plasma membrane which interacts with PrsP which is secreted from stigmatic tissue. When both have the same haplotype, an influx of Ca²⁺ into the pollen is triggered, inducing pollen death. There is no interaction between proteins encoded by different haplotypes.

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Parthenogenesis

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Apomixis where an embryo develops from the egg without fertilization. Fertilization may be necessary to trigger growth of the endosperm, depending on species.

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Peaches and cream sweet corn

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A self-cross of plants with Yy genotype. The endosperm genotype can be YYY, YYy, Yyy, or yyy, producing the variation in kernel yellow colour.

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Polar nuclei

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Two nuclei, one derived from each end of the embryo sac, which become centrally located in the central cell. Fuse with a sperm cell nucleus to form the primary triploid endosperm nucleus.

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Pollinatioin

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Plants can naturally cross- or self-pollinate, with a percentage continuum across species. Pollination biology involves flower morphology, timing of flower opening relative to anthesis and stigma receptivity, and genetic mechanisms. To determine the percentage of self- and cross-pollination of a plant, surround a homozygous recessive plant with homozygous dominant plants; progeny which display the dominant phenotype are a result of cross-pollination.

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Polyploidy

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An important aspect of plant genetics. Many plants are polyploid, including alfalfa, potato, banana, wheat, and canola. Segregation ratios are more complex.

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Protandry

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Pollen shed occurs before the stigma is receptive. A timing mechanism that results in cross-pollination. Includes carrot.

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Protogyny

answer

The stigma matures and ceases to be receptive before pollen is shed. A timing mechanism that results in cross-pollination. Includes raspberries and black pepper.

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Pseudogamy

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Apomixis where pollen is necessary to produce apomitic seeds, but the sperm and egg do not unite to form a zygote. It may be necessary for an endosperm to develop in some cases.

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Randomized complete block design

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An experimental design where the field is broken into blocks, and replications are randomized within the blocks. Reduces the effect of variables across the field.

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Russian dandelion

answer

A type of dandelion from Kazakhstan which produces natural rubber. It can be a temperate crop. There are social and environmental issues with rubber trees, and this could be a solution. Rubber is a strategic resource that is needed for many things.

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S locus

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The locus which controls self-incompatibility. Alleles are actually haplotypes, with parts that relate to pistils and pollen SI compatibility

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Seed

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A structure which varies with species, and presence or absence of endosperm. Contains zygotic and maternal tissues, which may have different genotypes. The seed coat comes from the ovule of the mother plant, and has the same genotype as the mother plant. The endosperm forms from fertilization of two identical nuclei in the central cell with a sperm cell, so it is triploid. The embryo forms from fertilization of the egg cell with another sperm cell, so it is diploid. There are three different genotypes present!

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Self-incompatibility (SI)

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A genetic system to prevent self-pollination. Genetic recognition of self-pollen, and fertilization is prevented. Controlled by the S locus. Includes gametophytic and sporophytic self-incompatibility. To determine which one, self-pollinate the plants and intermate progeny. One can overcome the SI reaction with special treatments of plants or flowers, such as altering temperature, using salt on the stigma, bud pollination, or increasing CO₂ concentrations.

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Self-pollination

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Union of gametes produced on the same plant. It is favoured by cleistogamy. Wild populations are heterogeneous. Individual plants are homozygous, and progeny from one pant is homogenous. Deleterious alleles are lost in the population. There is no inbreeding depression. Favourable alleles are slow to spread in a population.

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Semigamy

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Apomixis where the sperm nucleus enters the egg, but does not fuse, and a haploid embryo develops that is chimeric with tissues of maternal and paternal origin.

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Sexual reproduction

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Gametes form and fuse to produce a new organism with a unique genotype. Self-pollination is still a type of sexual reproduction. It is beneficial because it enables recombination of genes and formation of new genomes for evolution.

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Solanaceae

answer

A family of plants which has non-self-recognition gametophytic self-incompatibility. The S locus is complex compared to other systems, containing an RNAse gene as the female determinant and several SLF/SFB genes as the male determinant. The RNAse is produced in the stigma and enters the pollen tube, degrading RNA and killing the male gametophyte, unless the enzyme can be deactivated by an SLF/SFB haplotype in the pollen which does not match that of the stigma.

question

Soybean

answer

Pollination occurs in the advanced bud stage when the stigma becomes receptive and anthers dehisce, before the flower opens. Cross-pollination occurs at around 1% in field conditions, and is rare across distances greater than 4.6 m. Some cultivars experience higher rates of cross-pollination. Some cultivars experience yield increase when pollinated by honey bees. Varieties belong to different maturity groups.

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Spike moss

answer

Selaginella
Lycopodiophyta
The oldest living vascular plant division. A primitive, seedless, vascular plant. Heterosporous, with motile sperm.
1. The sporophyte produces microsporangium and megasporangium in the axils of sporophylls.
2. The microspore mother cells undergo meiosis, producing four haploid microspores each, which are released onto the soil.
3. The megaspore mother cells undergo meiosis, producing four haploid megaspores each, but three die, and only one is released onto the soil.
4. Microspores develop into microgametophytes. The cell divides within the microspore wall, becoming multicellular. An outer jacket of cells form, as well as an antheridium which produces biflagellate sperm. The microgametophyte cracks open and releases the sperm.
5. Megaspores develop into a multicellular megagametophyte, which has an archegonium that produces eggs and ruptures through the outer wall.
6. Sperm swim to the archegonium in a film of water and fertilize the eggs, forming a diploid zygote.
7. The zygote develops into the sporophyte which remains embedded in the megagametophyte.

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Sporangium

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A multicellular structure in which spores are produced.

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Spore

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A reproductive cell in plants.

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Spore mother cell

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A diploid cell that undergoes meiosis to produce four haploid cells.

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Sporophyte

answer

The spore producing diploid phase in the life cycle of a plant having alternation of generations. It is the plant itself.

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Sporophytic apomixis

answer

Adventitious embryony
Apomixis where one or more diploid cells of the ovule integuments or ovary wall undergo mitosis to form a diploid embryo, or embryos. The megaspore mother cell undergoes meiosis normally to form a haploid megaspore, which undergoes mitosis normally to form an embryo sac. Fertilization is required for endosperm development, and also fertilizes the haploid egg. Depending on the species, multiple viable embryos may be produced in one seed. Sometimes the sexually produced embryo fails to mature or germinate. Common in citrus.

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Sporophytic self-incompatibility

answer

Incompatibility is determined by the genotype of the plant from which the pollen arose. The father plant deposits proteins on the exine coating of the pollen grains. The site of action is the stigma surface. Can be co-dominant or dominant. Found in the Brassicaceae family.

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Synergids

answer

Two ephemeral cells lying close to the egg in the mature embryo sac of the ovule of flowering plants. Release compounds that attract the pollen tube.

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Tomato

answer

Fertilization takes 50 hours.

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Vascular system

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Consists of xylem and phloem. Transports water and nutrients. Absent in non-vascular plants. The first vascular plants were seedless.

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Vegetative cell

answer

One of the cells of the pollen grain. It is larger than the generative cell, and produces the pollen tube. Its nucleus goes down the style first. It bursts when it reaches the synergids.

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Vegetative reproduction

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Asexual reproduction without formation of a seed. Sporophytic tissue breaks or naturally produces clones. Includes stolons of strawberries, tubers of potatoes, adventitious shoots of bananas, and rhizomes of iris and ginger.

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Witch hazel

answer

Fertilization takes 5 - 7 months. Pollination occurs in the autumn, and fertilization occurs in the spring.

Plant Genetics: Quiz 1 – Flashcards

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