09.29.11 - Lecture 8. Interactions between genes and...

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Unformatted text preview: Lecture 8. Interactions between genes and alleles Readings: Chapt 6 Outline 1.Back to tetrad analysis 2.Centromere mapping 3.The mechanism of recombination 4.Interactions between alleles and genes a. codominance and partial dominance b. epistasis 5.Complementation analysis and gene pathways Meiosis products from yeast two haploids (ab and ++) combine to make diploid Scenario: a and b are on different chromosomes NO crossing over between gene and centromere ARRANGEMENT #1 Meiosis I Meiosis II a a + + diploid undergoes meiosis b b + + a a b b + + + + a b a b + + + + Meiosis products from yeast two haploids (ab and ++) combine to make diploid Scenario: a and b are on different chromosomes crossing over between one gene and centromere Meiosis I Meiosis II a a + + diploid undergoes meiosis b b + + a + + + a b + b a + + + a + b b Meiosis products from yeast two haploids ( ab and ++ ) combine to make diploid Scenario: a and b are on different chromosomes No crossing over #1 a b a b + + + + No crossing over #2 + b + b a + a + crossing over a and centromere a b + + a + + b PD NPD TT PD = NPD for genes on different chromosomes PD = NPD for genes on different chromosomes Meiosis products from yeast two haploids (ab and ++) combine to make diploid diploid undergoes meiosis Scenario: a and b are on same chromosome No crossing over Meiosis I Meiosis II a b a b + + + + + + + + a b a b a b a b + + + + Meiosis products from yeast two haploids (ab and ++) combine to make diploid diploid undergoes meiosis Meiosis I Meiosis II a b a b + + + + Scenario: a and b are on same chromosome crossing over between A and B + b + + a b a + a b a + + b + + yeast tetrads two haploids (ab and ++) combine to make diploid Scenario: a and b are on same chromosome No crossing over a b a b + + + + crossing over a b + b a + + + How can we get non-parental ditypes (NPD) for genes on the same chromosome? Parental ditype (PD), Non-parental ditype (NPD), or Tetratype (TT)? 4-strand double crossovers create NPD tetrads a b a b + + + + Parental type a b and + + a b a b + + + + a b a b + + + + 2-strand 3-strand 4-strand Hint: Trace out from centromere gametes produced? PD, NPD, or TT? ?/4 R gametes? Genetic distance: # R x 100 Total (1/2)TT +(1)NPD Total tetrads x 100 = # cM Genetic mapping in yeast 1. PD = NPD? if yes, different chromosomes if no, same chromosome ( PD >> NPD) 1. If on same chromosome, what is the distance between genes? NPD + 1/2 TT x 100 = # cM Total gametes Does not take double crossovers into account You do not need to know how to account for DR in yeast or Neurospora crosses Genetic mapping in yeast A his4 haploid mutant is mated to a arg3 haploid mutant. The following tetrads are observed: his4 + his4 arg3 his4 + his4 + his4 arg3 his4 arg3 + arg3 + + + + + arg3 + + + arg3 356 567 370 5 45 120 For dataset 1, what is the genetic distance between them?...
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09.29.11 - Lecture 8. Interactions between genes and...

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