Chapter 11, Problem 17TYU

INTERPRET DATA Using the graph in Figure 11-20, determine how many offspring were involved in the hypothetical cross studying skin color. What percentage had the lightest skin possible? the darkest skin possible?

Figure 11-20 Polygenic inheritance in human s pigmentation

This simplified example assumes that skin pigmentation in humans is governed by alleles of three unlinked loci. The alleles producing dark skin (A, B, and C) are represented by capital letters, but they are not dominant. Instead, their effects are additive. The number of dark dots, each signifying an allele producing dark skin, is counted to determine the phenotype. A wide range of phenotypes is possible when individuals of intermediate phenotype mate and have offspring (AaBbCc × AaBbCc). The expected distribution of phenotypes is consistent with the superimposed normal distribution curve.