Lecture 9- Mapping to Sex Linkage Two Linked Genes-If two genes, P and Q are i) linked in “trans” (repulsion) and ii) seperated by 20 map units, what would be the frequency of homozygous recessive offspring from a PpQq x PpQq cross? …. < 25% Map Distance-The % of recombinant progeny from a test cross -If you count the recombinant offspring, you can determine how far away the genes are on the chromosome -Recombination frequencies can be used to build genetic maps showing the relative location of genes on chromosomes -Genes a and c are located so far apart that a crossover almost always occurs between them.-Therefore, the % recombinant progeny will be 50%- just as it would be if the genes were on separate chromosomes-Therefore, these genes would appear to be unlinked -Genes a and b, and b and c, however, are close enough to show linkage; a and c must therefore also be linked Sex Chromosomes-Recall for humans…. -X is much larger than Y
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