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Lecture 7: Recombination mapping

Lecture 7: Recombination mapping. Reminders:. Exam 1 is next Tuesday, 2/8 Quiz 1 grades are posted on the course website Quiz 1 key will be posted on the website by the end of Friday. Crossing over produces new combinations of alleles. Independent assortment: recombinant frequency = 50%.

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Lecture 7: Recombination mapping

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  1. Lecture 7:Recombination mapping

  2. Reminders: Exam 1 is next Tuesday, 2/8 Quiz 1 grades are posted on the course website Quiz 1 key will be posted on the website by the end of Friday

  3. Crossing over produces new combinations of alleles

  4. Independent assortment: recombinant frequency = 50% Complete linkage (no crossover): recombinant frequency = 0% Linkage with crossover: recombinant frequency = 0<x<50%

  5. Recombination frequency is proportional to the distance between two genes genes close together: few recombinants genes far apart: many recombinants

  6. Map units are based on recombination frequency

  7. Example 3-point test cross: 3 Drosophila alleles (autosomal): eye color: v (vermillion) or v+ (wild type, red) wing veins: cv (no cross vein) or cv+ (wild type) wing edges: ct (cut) or ct+ (wild type) P v+ /v+cv /cv ct/ct X v/vcv+/cv+ ct+ /ct+ Input gametes: v+ cv ct AND vcv+ ct+ F1 trihybridv+ /vcv+ /cv ct+ /ct TEST CROSS: v+ /vcv+ /cv ct+ /ctX v/vcv/cv ct/ct F1 trihybrid female tester male

  8. Example of a 3 point test cross Input gametes: v+ cv ct AND vcv+ ct+ F2 progeny:

  9. Step 1: identify non-crossover classes: NCO NCO

  10. Step 2: identify double crossover classes DCO DCO

  11. Step 3: calculate recombinant frequencies: R R R R DCO DCO

  12. Recombinant frequency for v and cv R R R R DCO DCO RF (v and cv) = (45 + 40 + 89 + 94 + 3 + 5) ÷ 1448 = 276 ÷ 1448 = .191 X 100% = 19.1%

  13. Recombinant frequency for v and ct R R DCO DCO RF (v and ct) = (89 + 94 + 3 + 5) ÷ 1448 = 191 ÷ 1448 = .132 X 100% = 13.2%

  14. Recombinant frequency for cv and ct R R DCO DCO RF (cvand ct) = (45 + 40 + 3 + 5) ÷ 1448 = 93 ÷ 1448 = .064 X 100% = 6.4%

  15. Step 4: construct the map highest recombination frequency means farthest apart Recombination frequency v and cv: 19.1 Recombination frequency v and ct: 13.2 Recombination frequency cv and ct: 6.4 v ct cv 13.2 m.u. 6.4 m.u.

  16. Short cut: using double recombinants to deduce gene order Double recombinants have the middle gene“flipped” relative to parental arrangement: parentals: vcv+ ct+ v+cv ct DCO’s: vcv+ ct v+cv ct+ must be in between v and cv

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