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Lecture 6

Lecture 6 - Linkage, Recombination and Mapping

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Biology 2581B
Jim Karagiannis

LECTURE 5: LINKAGE, RECOMBINATIONAND MAPPING Key Concepts 1. Genetic linkage 2. Recombination frequency 3. Interference 4. Double strand break model of recombination • Degrees of Freedom = number of classes – 1 = 3 • df = 3, p-value = 0.05; 7.815 • Therefore, we conclude that the observed differences from the expected 1:1:1:1 ratio are not due to sampling error i.e. we reject the null hypothesis Two Critical Questions: • What is the genetic basis for the deviation from the expected 1:1:1:1 ratio? • Why is there an excess ofAaBb and aabb flies (and a • deficiency ofAabb and aaBb flies) in some trials, while in others this pattern is reversed? • In addition to the independent assortment of homologous chromosomes during meiosis, crossing over between two nearby loci on the same chromosome provides an alternative mechanism of deriving recombinants • Recombination results from reciprocal exchanges between homologous chromosomes (see figures 5.6, 5.7) • The synaptonemal complex aligns homologous chromosomes • Thus, in response to our two questions posed earlier: o Crossing over between two loci in close physical proximity on the same chromosome during meiosis I is the genetic basis of the deviation from the expected 1:1:1:1 phenotypic ratio o Arrangement (cis or trans) of the alleles on the chromosome determines the recombinant or parental
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