Introduction to Genetic Analysis 53

Introduction to - 44200_02_p27-72 11:38 AM Page 52 52 Chapter 2 Patterns of Inheritance consists of half red-eyed and half white-eyed ies of both

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consists of half red-eyed and half white-eyed Fies of both sexes. Hence in sex linkage, we see examples not only of different ratios in different sexes, but also of dif- ferences between reciprocal crosses. Note that in Drosophila, eye color has nothing to do with sex determination, so we see that genes on the sex chromosomes are not necessarily related to sexual func- tion. The same is true in humans: pedigree analysis has revealed many X-linked genes, yet few are related to sexual function. The eye color example concerned a recessive abnor- mal allele, which must have originally arisen by muta- tion. Dominant mutant alleles of genes on the X also arise. These show the inheritance pattern corresponding to the wild-type allele for red eyes in the example above. However, in such cases the wild-type allele is re- cessive. The ratios obtained are the same as in the above example. be obscured by inheritance of the recessive allele from a heterozygous mother as well as the affected father.) 3. None of the sons of an affected male show the phenotype under study, nor will they pass the condition to their offspring. The reason behind this
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.

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