LINKAGE AND - When this"individual" makes gametes we can say that recombination occurs with a frequency(or probability" r" Thus

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LINKAGE AND RECOMBINATION Gene loci on the same chromosomes are generally considered to be in the same linkage group because the alleles on each chromosome can be inherited as a "linked set" (like beads on the same string). But a chromosome can be long enough that the probability of a crossover (=recombination) event some where along the chromosome is very high. Thus genes at different ends of same chromosomes can be effectively unlinked . Conversely genes close to each other on the chromosome are usually tightly linked because the probability of a recombination event between them is very low. Consider a pair of chromosomes, and think about the gene loci at each ends. Each locus carries two alleles and we will consider the case where the two alleles are different (each locus is heterozygous):
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Unformatted text preview: When this "individual" makes gametes, we can say that recombination occurs with a frequency (or probability) " r ". Thus recombination does not occur with a probability (1-r) . When recombination does not occur the gametes produced will be A B and a b (note only one letter is used at each locus because gametes are haploid); when recombination does occur the gametes will be A b and a B . (see figure 2.7, pg. 34). If the loci were on separate chromosomes (unlinked) and we were "given" a gamete with the "A" allele, 1/2 of the gametes would be AB and 1/2 would be Ab (the under score is omitted as a shorthand notation). If we were "given" a gamete with the "a" allele, 1/2 the gametes would be ab and 1/2 would be aB. These four gametes would be in the relative proportions 1:1:1:1....
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This note was uploaded on 11/05/2011 for the course BIOLOGY MCB2010 taught by Professor Jessicadigirolamo during the Fall '10 term at Broward College.

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