Ôn tập sinh học tdl121 gen 03 principles of heredity v2

21/03/01 Principles of heredity Materials were extracted from Hartwell et al., 2018 Genetics: from genes to genomes, 6th edition and Pierce, 2012 Genetics: a conceptual approach, 4th edition unless cited otherwise Content • Mendel’s laws of heredity • Extensions to Mendel’s laws • Sex determination and sex-related characteristics • Linkage, recombination and gene mapping 21/03/01 Content • Mendel’s laws of heredity • Extensions to Mendel’s laws • Sex determination and sex-related characteristics • Linkage, recombination and gene mapping The puzzle of inheritance • People domesticated plants and animals, selected and created many breeds but did not know • What is inherited? • How is it inherited? • What is the role of chance in heredity? • Misconceptions • The homunculus: one parent contributes most to an offspring’s inherited features • Blended inheritance: traits become mixed and forever changed in the offspring Hartwell et al., 2018 21/03/01 Discoverers of Mendel’s laws Hartwell et al., 2018 Mendel’s garden and microscope Hartwell et al., 2018 21/03/01 Factors contributed to Mendel’s success • The garden pea Pisum sativum Hartwell et al., 2018 The garden pea (Pisum sativum) • Bisexual flowers, self-fertilizing: pure breed Lưỡng tính, tự thụ: dịng • Feasible cross-fertilization: hybrid • Generating many seeds: statistical analysis Hartwell et al., 2018 21/03/01 Factors contributed to Mendel’s success • The garden pea Pisum sativum • Discrete trait with antagonistic forms Hartwell et al., 2018 Studied traits with antagonistic forms Hartwell et al., 2018 10 21/03/01 Factors contributed to Mendel’s success • The garden pea Pisum sativum • Discrete trait with antagonistic forms • Pure-breeding lines Lai dịng • Carefully controlled crosses, reciprocal crosses • Numerical analysis of large numbers of plants and seeds • Mendel was a brilliant practical experimentalist Hartwell et al., 2018 11 Dominant phenotype Phenotype expressed by heterozygotes and identical to only one of the homozygotes Kiểu hình dị hợp tử, giống với kiểu hình đồng hợp tử Hartwell et al., 2018 12 21/03/01 Quy luật phân ly The law of segregation Hartwell et al., 2018 13 Yellow F2 peas are either pure breeding or hybrid Hartwell et al., 2018 14 21/03/01 Phép lai phân tích The testcross Hartwell et al., 2018 15 The testcross Hartwell et al., 2018 16 21/03/01 Quy luật phân ly độc lập The law of independent assortment Hartwell et al., 2018 17 Molecular basis of seed shape trait Sbe1: Starch-branching enzyme Hartwell et al., 2018 18 21/03/01 Molecular basis of seed color trait Sgr: Stay green Hartwell et al., 2018 19 Mendelian inheritance in humans • Most common and obvious human phenotypes arise from the interaction of many genes • Roughly 6000 single-gene traits known in humans as of 2016 • Genetic diagnosis Hartwell et al., 2018 20 10 21/03/01 Chromosomal interference • 𝑅𝐹𝑣𝑔−𝑏 = 0.177, 𝑅𝐹𝑣𝑔−𝑝𝑟 = 0.123 • 𝑅𝐹𝑏−𝑝𝑟 = 0.064 ã = 0.123 ì 0.064 = 0.0079 • 𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑 𝑅𝐹𝐷𝐶𝑂 = 13+9 4197 = 0.0052 • 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑜𝑓 𝑐𝑜𝑖𝑛𝑐𝑖𝑑𝑒𝑛𝑐𝑒 = hệ số phù hợp 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 𝑒𝑥𝑝𝑒𝑐𝑡𝑒𝑑 = 0.0052 0.0079 = 0.66 𝐼𝑛𝑡𝑒𝑟𝑓𝑒𝑟𝑒𝑛𝑐𝑒 = − 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑜𝑓 𝑐𝑜𝑖𝑛𝑐𝑖𝑑𝑒𝑛𝑐𝑒 = − 0.66 = 0.34 Hartwell et al., 2018 Hệ số nhiễu 115 Recombination hotspots Trật tự gen Khoảng cách gen khác Hartwell et al., 2018 116 58 21/03/01 Drosophila melanogaster genetic map Hartwell et al., 2018 117 Essential concepts • A series of two-point crosses can establish the order of linked genes and the distances between them through pairwise analysis of recombination frequencies • Three-point testcrosses can refine map distances and reveal the existence of crossover interference, a phenomenon that distributes among all chromosomes the limited number of crossovers that occur in each meiosis • Although genetic maps provide an accurate picture of gene order on a chromosome, the distances measured between genes can be misleading • Genes in a linkage group are by definition syntenic With enough mapped genes, the entire chromosome becomes a single linkage group Hartwell et al., 2018 118 Syntenic: đoạn NST, bảo thủ 59 21/03/01 Chi-square test (𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑 − 𝑛𝑢𝑚𝑏𝑒𝑟 𝑒𝑥𝑝𝑒𝑐𝑡𝑒𝑑)2 Χ =∑ 𝑛𝑢𝑚𝑏𝑒𝑟 𝑒𝑥𝑝𝑒𝑐𝑡𝑒𝑑 degrees of freedom (df) = number of classes - 119 Kiểm định di truyền liên kết phân ly độc lập Hartwell et al., 2018 Tetrad analysis in fungi Phân tích 120 60 21/03/01 The life cycles of the yeast Saccharomyces cerevisiae Hartwell et al., 2018 121 Three tetrad types produced by meiosis of dihybrid yeast Hartwell et al., 2018 122 hai loại giao tử giống bố mẹ Kiểu Kiểu khác bố mẹ Tần suất tái tổ hợp = (4*NPD + 2*T)/(4*(PD + NPD + T) 61 21/03/01 Parental ditype from unlinked genes Hartwell et al., 2018 123 Nonparental ditype from unlinked genes Hartwell et al., 2018 124 62 21/03/01 Tetratype from unlinked genes Hartwell et al., 2018 125 Parental ditype from linked genes Hartwell et al., 2018 126 63 21/03/01 Nonparental ditype from linked genes Hartwell et al., 2018 127 Tetratype from linked genes Hartwell et al., 2018 128 64 21/03/01 Tetrad analysis • If PDs ≈ NPDs, two genes are unlinked • If PDs » NPDs, two genes are linked 𝑇 𝑅𝐹 = 𝑡𝑜𝑡𝑎𝑙 𝑡𝑒𝑡𝑟𝑎𝑑𝑠 𝑁𝑃𝐷 + Hartwell et al., 2018 129 PDs » NPDs → two genes are linked 70 3+ 𝑅𝐹 = = 0.19 200 Hartwell et al., 2018 130 65 21/03/01 The life cycles of the yeast Neurospora crassa Hartwell et al., 2018 131 Ordered tetrads Hartwell et al., 2018 132 66 21/03/01 Two segregation patterns in ordered asci Hartwell et al., 2018 133 Ordered tetrad analysis 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒𝑔𝑒𝑛𝑒↔𝑐𝑒𝑛𝑡𝑟𝑜𝑚𝑒𝑟𝑒 = 𝑀𝐼𝐼 × 𝑇𝑜𝑡𝑎𝑙 𝑡𝑒𝑡𝑟𝑎𝑑𝑠 Hartwell et al., 2018 134 67 21/03/01 Rules for tetrad analysis Hartwell et al., 2018 135 Essential concepts • A tetrad is the group of four haploid spores within an ascus that results from a single meiosis in fungi Bộ nhóm bào tử đơn bội nang bào tử, kết trình giảm phân nấm • In a parental ditype (PD), a tetrad has four parental spores; in a nonparental ditype (NPD), a tetrad contains four recombinant spores; in a tetratype (T), an ascus contains two different parental spores and two different recombinant spores • When a dihybrid sporulates, if PD tetrads are equal to NPD tetrads, the genes in question are unlinked; when PDs greatly outnumber NPDs, the genes are linked • Analysis of unordered tetrads reveals linked genes and the map distance between them; analysis of ordered tetrads further allows determination of the distance between a gene and the centromere Hartwell et al., 2018 136 Phân tích khơng có trình tự cho biết gen liên kết với khoảng cách chúng, phân tích có trình tự cho biết khoảng cách gen tâm động 68 21/03/01 Mitotic recombination and genetic mosaics 137 Genetic mosaicism Thể khảm Hartwell et al., 2018 Hartwell et al., 2018 138 69 21/03/01 Mitotic recombination results in a twin spot Hartwell et al., 2018 139 Mitotic recombination results in a single yellow spot Hartwell et al., 2018 140 70 21/03/01 Mitotic recombination results in a single singed spot Hartwell et al., 2018 141 Mitotic recombination results in sectored yeast colonies ADE2/ade2 ade2/ade2 Hartwell et al., 2018 142 71 21/03/01 Mitotic recombination can contribute to cancer 40% Hartwell et al., 2018 143 Essential concepts • Twin spots are a form of genetic mosaicism; these spots occur when mitotic recombination gives rise to two clones of cells having reciprocal mutant genotypes and phenotypes • Mitotic recombination can also produce sectored colonies in diploid yeast, in which part of a colony has a recognizable mutant phenotype Hartwell et al., 2018 144 72