Introduction to Genetic Analysis 44

Introduction to Genetic Analysis 44 - 44200_02_p27-72...

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43 2.1 Autosomal inheritance that both male and female progeny are affected, we can assume that we are most likely dealing with simple Mendelian inheritance of a gene on an autosome, rather than a gene on a sex chromosome. The following typical pedigree illustrates the key point that affected children are born to unaffected parents: gotes are much more common than recessive homozy- gotes is that to be a recessive homozygote, both parents must have had the a allele, but to be a heterozygote, only one parent must carry it. The formation of an affected person usually de- pends on the chance union of unrelated heterozygotes. However, inbreeding (mating between relatives) in- creases the chance that two heterozygotes will mate. An example of a marriage between cousins is shown in Fig- ure 2-13. Individuals III-5 and III-6 are ±rst cousins and produce two homozygotes for the rare allele. You can see from Figure 2-13 that an ancestor who is a heterozy- gote may produce many descendants who also are het- erozygotes. Hence two cousins can carry the same rare recessive allele inherited from a common ancestor. For
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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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