Plant Genetics: Quiz 5 – Flashcards
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Unlock answers| ?-1,3-glucanase |
| Breaks down glucan in fungus cell walls. Used by plants to defend against fungal pathogens. |
| Allohexaploid |
2n = 6x There is an AABBDD genome designation. Includes wheat and oats. |
| Alloploid |
| Having sets of chromosomes from different species. Includes allohexaploids. Includes oat, wheat, cotton, tobacco, and sugarcane. Homologous chromosome pairs have bivalent pairing, producing classical Mendelian segregation; there is no random chromosome assortment. Accounts for more cultivated species than autoploids. Often self-pollinators with low inbreeding depression. Certain genetic mechanisms prevent homeologous pairing of chromatids from separate genomes. Mutation can weaken these mechanisms, causing some alloploids to have tetrasomic inheritance, such as quinoa. |
| Aneuploidy |
| Having a variaion in complete sets of chromosomes. Some of the sets are incomplete. Includes trisomics. |
| Autotetraploid |
2n = 4x Theere is an AAAA genome designation. Includes alfalfa and potato. Slow growing plants with dark green leaves, and a larger plant size than diploids. Have increased cell size. Depending on species, pairing of four chromosomes can occur as two bivalents or one quadrivalent for each chromosome. |
| Autoploid |
| Having multiple sets of chromosomes from one species. Includes autotetraploids. Includes potato, alfalfa, coffee, banana, peanut, and snapdragon. Segregation ratios vary depending on how chromosomes pair, in bivalents or quadrivalents, and position of the gene relative to the centromere. In gamete production there can be random chromosome or random chromatid assortment. |
| Barley |
| 2n = 2x = 14 |
| Basic chromosome number (x) |
Basic genome The number of chromosomes in one complete copy. |
| Bivalent pairing |
| The pairing of two chromosomes. A type of pairing in an autotetraploid. Four identical chromosomes pair as two bivalents, which go to opposite poles in meiosis I, and sister chromatids separate in meiosis II. Gametes are n = 2x, with two copies of each chromosome. Each chromosome has an equal chance of pairing with each other, with 6 possible outcomes of gametes. Has random chromosome assortment. Occurs in tetraploid alfalfa. |
| Brassica carinata |
BBCC An allotetraploid formed from the cross of B. nigra and B. oleracea. |
| Brassica juncea |
AABB An allotetraploid formed from the cross of B. nigra and B. rapa. |
| Brassica nigra |
BB A diploid species which crossed with B. rapa to produce B. juncea, and with B. oleracea to produce B. carinata. |
| Cabbage |
Brassica oleracea CC 2n = 2x = 18 A diploid species which naturally crossed with B. nigra to produce B. carinata, and with B. rapa to produce B. napus. It was crossed with radish to form raphanobrassica. |
| Canola |
Brassica napus AACC An allotetraploid formed from the cross of B. rapa and B. oleracea. |
| Cas9 |
| A protein found in bacteria for defence against viruses. In plants it is used to cause mutations in CRISPR-Cas9. |
| Chenopodium |
x = 9 A genus which inludes quinoa. |
| Chitinase |
| Breaks down chitin in fungus cell walls. Used by plants to defend against fungal pathogens. |
| Colchicine |
| A chemical which blocks spindle fibres that pull chromatids apart to the two daughter cells. Without spindle fibres, only one daughter cell forms, and chromosome number is doubled. A man-made change in mitosis that can cause polyploidy. Used to produce raphanobrassica. Applied to dividing cells. Can produce octoploids if left for too long, but there is a limit to what the cell can contain. |
| CRISPR-Cas9 |
| A big advancement in the field of genetics. Any sequence can be inserted to cause a mutation. A double stranded break causes a small insertion or deletion, or splicing in of a sequence. Can be used to determine the gene of a mutation; if you mutate a gene and the phenotype is the same as the mutant, then that is the mutated gene. |
| Cytogenetics |
| Reveals the number of diploid progenitors vs. polyploids. It is a dying field. Chromosomes can sometimes look like rings when they are tangled in anaphase during recombination, connected at chiasmas. Can be used to determine the parent species of an alloploid. Cross the alloploid to candidate species. If there are bivalents and univalents, this is the species. If there are only univalents in the progeny, this is not the species. |
| Datura innoxia |
| A plant which was used for trisomic line experiments. Has 12 chromosomes and 12 trisomic phenotypes. |
| Diploid |
2n = 2x n = x In a gene with two alleles, there are two homologous chromosomes, and possible genotypes are AA, Aa, and aa. |
| Diploid canola |
Brassica rapa AA A diploid species which crossed with B. nigra to produce B. juncea, and with B. oleracea to produce B. napus. |
| Disomic inheritance |
| Occurs for independently assorting genes in an allotetraploid. A self of ABaBADaD where B and D denote genome, produce 15 A___:1 aaaa. Similar to independent segregation of genes on different chromosomes. Behaves like a diploid. Sister chromatids can only pair with those from the same genome. |
| Duplex |
| The AAaa genotype in a tetraploid. With random chromosome assortment, possible gametes are 1 AA:4 Aa: 1 aa, and the F2 segregation is 1 AAAA:8 AAAa:18 AAaa:8 Aaaa:1 aaaa. With complete dominance this is 35 A___:1 aaaa. |
| dyad and MiMe |
| A meiotic mutation. Meiosis of the mother cell is replaced by mitosis. The mega- or microspore mother cell is 2n, and undergoes meiosis to form 2n gametes. |
| Einkorn wheat |
Triticum monococcum AA |
| Emmer wheat |
Triticum turgidum AABB Pasta wheat Allotetraploid wheat formed from the cross of einkorn wheat (AA) and T. searsii (BB). The F1 was AB, and must have had chromosome doubling to produce AABB. Crossed with T. tauschii to form hexaploid wheat. Cultivated 10,000 years ago. |
| Fluorescent in situ hybridization (FISH) |
| A molecular method of placing genes on specific chromosomes. The DNA sequence or gene is cloned and hybridized to chromosomes. This can link DNA sequences to a numbered chromosome with particular size and cytological characteristics. One can identify entire linkage groups to a chromosome this way. |
| Gametophyte |
| n |
| Genetic map |
| Mathematically derived, based on recombinant genes. Not always proportional to the physical map. Chromosome size can be estimated incorrectly. FISH and trisomic lines are used to determine which chromosome is which. |
| Glycine |
| G. tomentella (DD) and G. canescens (AA) are crossed, and the F1's chromosomes doubled to produce AADD, which is then back-crossed to G. canescens, producing an AAD individual, which has 20 bivalents and 20 univalents (60 chromosomes total), which can be seen with cytogenetics. |
| Glycine canescens |
2n = 40 AA |
| Glycine tomentella |
2n = 40 DD A species of soybean. |
| Hexaploid |
2n = 6x n = 3x |
| Hexaploid wheat |
Triticum aestivum AABBDD Bread wheat An allohexaploid formed from the cross of emmer wheat (AABB) and T. tauschii (DD) which occured 8,000 years ago. The F1 was ABD and must have had chromosome doubling to produce AABBDD. |
| High-throughput sequencing |
| Technology which has made mapping a lot quicker. All mutants are sequenced, and the location of mutations can be found. With independent assortment, markers segregate 1:2:1 (about 50% A, 50% B), except in areas with mutations. |
| Independent mutants |
| Starting in 2000, DNA insertion mutagenesis was done in Arabidopsis, randomly transforming with T-DNA from Agrobacterium tumefaciens (now called Rhizobium radiobacter), producing several hundred thousand insertion lines. Determined knockout function of genes, and figured out the sequence of each. |
| Kawahigashi et al, 2011. |
| Made a high-density map of the ds1 locus in sorghum, with simple sequence repeat markers. Found a candidate gene, LRR-RK. A computer program found genes using TATA boxes and sequencing. The candidate, or ORF2, was expressed in leaves and stems (where resistance reaction occurs) but not roots or flowers. Reinserted the gene to prove that it causes resistance. |
| Leucine-rich repeat receptor kinase (LRR-RK) |
| A family of genes which may provide resistance to target leaf spot in sorghum. Expressed in the leaf and stems, but not in roots or flowers. A recessive mutation confers resistance. |
| Meiosis |
| In meiosis I chromosomes replicate, pair, and crossover. Paired chromosomes align on the metaphase plate, and homologous chromosomes are pulled to two poles. In meiosis II sister chromatids are pulled to opposite poles. The planes of division are perpendicular for the two groups of chromosomes when chromatids are separating, forming four haploid cells. |
| Mitosis |
| Chromosomes replicate and align on the metaphase plate. Sister chromatids separate to two poles, forming two daughter cells. Chromosome number is maintained. |
| Nulliplex |
| The aaaa genotype in a tetraploid. |
| ods1 and tam |
| A meiotic mutation. Meiosis I proceeds normally, producing two sets of chromosomes. Meiosis II is arrested and division stops. Forms two daughter cells each with one set of replicated chromosomes. Sister chromatids split and each cell has the sporophytic chromosome number. |
| Parthenocarpy |
| A plant produces fruit without fertilization. Can produce seedless fruits. |
| Pentaploid |
2n = 5x n = sterile |
| Polyploid |
| Having more than 2 basic, complete sets of chromosomes. 30 - 50% of angiosperms are polyploid, 70% of grasses, and 23% of legumes. Can be man-made by somatic doubling (change in mitosis), or can be natural from somatic doubling or 2n gametes (a change in meiosis). Natural production of 2n gametes occurs in alfalfa, diploid potatoes, and low-ploidy strawberries. |
| ps1 and jason |
Parallel spindles A meiotic mutation. Meiosis I proceeds normally, but in meiosis II the spindle fibres align in a parallel fashion, formign two cells with sporophytic chromosome number. |
| Quadriplex |
| The AAAA genotype in a tetraploid. |
| Quadrivalent pairing |
| A cross-shaped formation of the pairing of four chromosomes in a tetraploid. The centromeres of each chromosome ends up in separate daughter cells. Genes close to the centromere have random chromosome assortment ratios. Genes distal to the centromere have random chromatid assortment ratios. Six combinations of centromeres are possible, same as with bivalent pairing. However, crossover events can occur between genes and centromeres, causing random chromatid assortment. It is convenient to derive gamete frequencies as a separate punnet square. Occurs in tetraploid potato. |
| Quinoa |
Chenopodium quinoa 2n = 4x = 36 An allotetraploid, but is functionally diploid in some cases. A superfood with high protein and balanced amino acids. Native to Peru and Bolivia, where it is a staple grain. Becoming popular all over the world. It has very small flowers, making effective emasculation for crosses impossible. It is self-pollinating, and has low inbreeding depression. It has disomic inheritance in some crosses, and tetrasomic inheritance in others. This is due to different recombination events between chromosomes in evolutionary history in different lines of quinoa; it forms quadrivalents in some chromosomes, and not in others. It could have disomic and tetrasomic inheritance occuring in the same cross; this confounds segregation ratios. |
| Random chromatid assortment |
| A possible segregation pattern in autoploids. Alleles on sister chromatids can occur in the same gamete. There is quadrivalent pairing. Genes are distal to the centromere by at least 50 cM; a crossover event can occur between the gene and the centromere. Because the alleles on the two sister chromatids are now associated with centromeres from different chromosomes, it becomes possible for these alleles to occur in the same gamete. To find gametes, produce a punnet square of all 8 chromatids. |
| Random chromosome assortment |
| A possible segregation pattern in autoploids. Alleles on sister chromatids cannot occur in the same gamete. Genes are proximal to the centromere, and are tightly linked to it. Sister chromatids always go to opposite poles, so must end up in different gametes. Occurs in bivalent pairing, and in quadrivalent pairing when there are no crossovers between the gene and the centromere. Each of the 8 chromatids have an equal chance of occurring in a gamete with all other chromatids, except for sister chromatids. |
| Raphanobrassica |
| A man-made allotetraploid. Made from a cross of cabbage, Brassica oleracea, and radish, Raphanus sativus, which are both 2n = 2x = 18. Produced a sterile F1 plant with 18 chromosomes that cannot pair in meiosis, and produces sterile gametes. Doubling of the chromosomes with colchicine produced 2n = 4x = 36; the plant produced gametes with balanced chromosomes, and is fertile. |
| Simplex |
| The Aaaa genotype in a tetraploid. With random chromosome assortment, possible gametes are 1 Aa:1 aa, and the F2 segregation is 1 AAaa:2 Aaaa:1 aaaaa. With complete dominance this is 3 A___:1 aaaa. With random chromatid assortment, possible gametes are 1 BB:12 Bb:1 bb, and the F2 segregation is 1 BBBB:24 BBBb:174 BBbb:360 Bbbb:225 bbbb. With complete dominance this is 2.5 B___:1 bbbb. |
| Somatic doubling |
Endomitosis A change in mitosis that can cause polyploidy. Chromosomes replicate but only one daughter cell is produced during mitosis. Sister chromatids break apart in one cell, and chromosome number is doubled. |
| Sorghum |
| Has a genome of 750 million bp. |
| Sporophyte |
| 2n |
| Strawberry |
2n = 8x AAA'A'BBB'B' An auto-allo-octoploid. A and A' are not identical, but are highly related. |
| Target leaf spot |
| One of the major sorghum diseases in southern Japan. Caused by a necrotrophic fungus, Bipolaris sorghicola. Resistance is controlled by a recessive gene, ds1. Loss of function or suppression of ds1 leads to resistance. |
| Tetraploid |
2n = 4x n = 2x In a gene with two alleles there are four homologous chromosomes, and possible genotypes are quadriplex, triplex, duplex, simplex, and nulliplex. There is bivalent pairing or quadrivalent pairing. |
| Tetrasmic inheritance |
| Pairing up in quadrivalents. Behaves like a tetraploid. has 35:1 segregation. |
| Triangle of U |
| Three diploid species, Brassica nigra, B. oleracea, and B. rapa, naturally give rise to three allotetraploid species, B. juncea, B. carinata, and B. napus. |
| Triplex |
| The AAAa genotype in a tetraploid. |
| Triploid |
2n = 3x n = sterile Synthesized by crossing a triploid with a diploid (4x) x (2x) > (3x). Desirable because they are seedless. Includes banana and seedless lime and watermelon. Sterile because three chromosomes cannot pair during meiosis. Usually, only two chromosomes can be paired in any one location. There can be a trivalent, or a bivalent and a univalent. In meiosis I, three homologous chromosomes separate to the poles with two at one pole and one at the other. Which chromosomes have one or two at each pole is random, so most gametes contain unbalanced sets of chromosomes and are non-viable. Theoretically, viable gametes with n = x or n = 2x are possible, but probability of them uniting to form a zygote are close to zero. The more chromosomes, the more rare viable gametes are. Can produce female gametes with one extra chromosome, n = x + 1, although this is rare; used to produce trisomics. |
| Trisomic |
2n = 2x + 1 An aneuploid. There is one extra copy of a given chromosome. The number of chromosomes a species has is the number of different trisomics that are possible. The additional chromosome can have profound effects on phenotype, and dosage effects may affect gene expression. Produces two types of female gametes (x + 1) and (x), and only one type of male gamete (x). Produces 1 triploid:1 diploid progeny when it is the female parent, and all diploid progeny when it is the male parent. The most common way they are produced: 1. Tetraploid crossed with diploid produces triploid: 4n x 2x > 3n. 2. Triploid is crossed with diploid, producing trisomic (n = x + 1) x (2n = x) > (2n = 2x + 1) |
| Trisomic lines |
| A classical method of placing genes on specific chromosomes. Cross a recessive mutation in a diploid to all possible trisomic lines (one for each chromosome). For the trisomic chromosome, it is AAA x aa. For all others it is AA x aa. If the mutation is on the trisomic chromosme, two types of progeny are produced: AAa and Aa. The trisomic progeny are selfed, producing gemale gametes 1 AA:2 Aa:2 A:1 a, and male gametes 2 A:1 a (only eggs can tolerate n = x + 1). All trisomic progeny have dominant phenotype, and diploids segregate 8:1. If the mutation is not on the trisomic chromosome, the mutation will segregate 3:1 in both trisomic and diploid F2 progeny. If one gene in a linkage group maps to a chromosome, the whole linkage group will map to that chromosome. |
| Triticum searsii |
BB Wild diploid wheat that crossed with einkorn wheat to form emmer wheat. |
| Triticum tauschii |
DD Wild diploid wheat that crossed with emmer wheat to form hexaploid wheat. It originated from a cross of einkorn wheat and T. searsii, separate from emmer wheat. |
| Ward, 2000 |
| Crossed quinoa plants to observe the disomic and tetrasomic segregation of this allotetraploid. Used cytoplasmic male sterile plants as female parents to overcome the difficulty of emasculating the flowers. |
| Wheat |
| A natural allohexaploid. Includes three cultivated species: einkorn (AA), emmer (AABB), and hexaploid (AABBDD), and two wild species: Triticum searsii (BB) and T. tauschii (DD). |
