IGA 8/e Chapter 2

Chapter Two 43–/r? ?R/r R/r–/rr/rR/–R/–R/–R/–r/rr/rBoyr/rSisterR/–b. Assuming the twins are identical, there might be either an environmentalcomponent to the expression of that gene or developmental noise (seeChapter 1). Another possibility is that the R allele is not fully penetrant andthat some genotypic “rollers” do not express the phenotype.74. Red hair runs in families, as in the following pedigree. (Pedigree from W. R.Singleton and B. Ellis, Journal of Heredity 55, 1964, 261.)a. Does the inheritance pattern in this pedigree suggest that red hair could becaused by a dominant or a recessive allele of a gene that is inherited in asimple Mendelian manner?b. Do you think that the red-hair allele is common or rare in the population as awhole?Answer:a. The inheritance pattern for red hair suggested by this pedigree is recessivesince most red-haired individuals are from parents without this trait.b. In most populations, the allele appears to be somewhat rare.