lec 4 Recomb- mapping_posted

Lec 4 Recomb- - B a Parental generation a Synapsis and crossing over B fertilization A b only two chromatids are involved in an exchange at any one

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
Chiasma Resolution of chiasmata. Each bivalent moves to the poles Anaphase Meiosis II Gametes from F1 parental parental recombinant recombinant x fertilization Parental generation F1 zygote mitosis S-phase enter meiosis a aB B A Ab b a B A b a B a a B B A A b b a a B b A A B b ab AB Synapsis of homologs Prophase I only two chromatids are involved in an exchange at any one point, but there may be two, three or four separate exchanges in a tetrad the larger the distance between markers along a chromosome, the higher the probability that a recombination event will occur between them Æ recombination frequency can serve as a measure of distance Synapsis and crossing over
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
9 : 3 : 3 : 1 Gg Ww G_W_ gg W_ G_ ww gg ww Genetic linkage and recombination gg WW x GG ww x gW Gw gametes Aa Bb aaBB x AAbb x aB Ab gametes 201 : 99 : 99 : 1 A_B_ aaB_ A_bb aabb F1 Aa Bb AB ab aB Ab gametes F1 F1 Test cross of F1 P P Gg Ww gg ww x 1 : 1 : 1 : 1 GgWw gg Ww Ggww ggww Test cross of F1 Aa Bb aabb x 1 : 9 : 9 : 1 AaBb aaBb Aabb aabb Why abnormal ratio? Independent segregation Linkage F1 Gg Ww GW gw Gw gW gametes 1 1 1 1 1 9 9 1 parental parental recombinant recombinant parental parental recombinant recombinant Using Punnett square leads to these proportions ratio ratio
Background image of page 2
aaBB AAbb x aB Ab gametes a B / A b F1 Aa Bb AB ab Ab aB gametes F1 P Test cross of F1 1 : 9 : 9 : 1 AB/ab aB/ab Ab/ab ab/ab 1 9 9 1 parental parental recombinant recombinant AABB aabb x AB ab gametes A B / a b F1 Aa Bb AB ab Ab aB gametes F1 P Test cross of F1 a B / A b a b / a b x AB / ab a b / ab x 9 : 1 : 1 : 9 AB/ab aB/ab Ab/ab ab/ab Linkage 9 1 1 9 recombinant recombinant parental parental coupling phase repulsion phase Parental gametes represent the same arrangement as in the P generation and are over represented. Recombinant gametes represent new allele combinations and are underrepresented. The genotypic make up of parental and recombinant classes depends on the original coupling of alleles
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Physical evidence that recombination is based on crossing over (Creighton & McClintock, 1931) C c wx Wx heterochromatin “knob” translocation from another chromosome C = colored kernel; c = colorless kernel Wx = starchy kernel; wx = waxy kernel in maize C c wx Wx c wx X c wx parental classes are: colorless, starchy (c Wx / c wx) and colored, waxy (C wx / c wx) recombinants classes are: colorless, waxy (c wx / c wx) and colored, starchy (C Wx / c wx) c wx ( This is a test cross. Recombination occurs in both parents but can only be detected in the heterozygote ) C Wx analyze recombinants cytologically c wx C Wx correlation between exchange of genetic and cytological markers
Background image of page 4
Using recombination to measure genetic distance Genetic distance between two genetic markers (e.g. genes): average number of crossovers between them Two point crosses: a B / A b x a b / a b A B / a b a B / a b A b / a b a b / a b Genotype of offspring 583 62 590 69 parental parental recombinant recombinant total # recombinant offspring total # offspring 62 + 69 62 + 69 + 583 + 590 == 131 1304 = Recombination frequency (RF) = 0.10 Map distance (A-B) = RF x 100 = 10 map units (m.u.) (or centiMorgans (cM)) A B 10 m.u.
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 07/17/2011 for the course BIO 151 taught by Professor Grinblat during the Summer '08 term at Wisconsin.

Page1 / 21

Lec 4 Recomb- - B a Parental generation a Synapsis and crossing over B fertilization A b only two chromatids are involved in an exchange at any one

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online