A dominant gene V in humans causes certain areas of the skin to become depigmented, a condition called "vitiligo." Albinism is the complete lack of pigment production and is produced by the recessive genotype aa. The albino locus is epistatic to the vitiligo locus. Another gene locus, the action of which is independent of the previously mentioned loci, is known to be involved in a mildly anemic condition called "thalassemia."
(a) When the adult progeny from parents both of whom exhibit vitiligo and a mild anemia is examined, the following phenotypic proportions are observed : 1/16 normal : 3/16 vitiligo : 1/8 mildly anemic : 1/12 albino : 3/8 vitiligo and mildly anemic : 1/6 albino and mildly anemic. What is the mode of genetic action of the gene for thalassemia? (b) What percentage of the viable albino offspring in part (a) would carry the gene for vitiligo? (c) What percentage of viable offspring with symptoms of mild anemia also show vitiligo?
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