62Chapter 2 •Patterns of Inheritancea.Deduce the most likely mode of inheritance.b.What would be the outcomes of the cousin mar-riages 139, 134, 233, and 238?Solutiona.The most likely mode of inheritance is X-linked dom-inant. We assume that the disease phenotype is domi-nant because, after it has been introduced into the pedi-gree by the male in generation II, it appears in everygeneration. We assume that the phenotype is X-linkedbecause fathers do not transmit it to their sons. If it wereautosomal dominant, father-to-son transmission wouldbe common.In theory, autosomal recessive could work, but it isimprobable. In particular, note the marriages between af-fected members of the family and unaffected outsiders.If the condition were autosomal recessive, the only way in which these marriages could have affected off-spring is if each person marrying into the family were a heterozygote; then the matings would be a/a(af-fected)3A/a(unaffected). However, we are told that4.
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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.