{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

lec 4 Recomb- mapping_posted

lec 4 Recomb- mapping_posted - B a Parental generation a...

Info icon This 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 a B B A A b b a A b B A A b b a a B B a a B B A A b b a a B b A A B b a B a b A B A b 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
Image of page 1

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

View Full Document Right 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
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
Image of page 3

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

View Full Document Right 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
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))
Image of page 5

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

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

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern