T3

Phenotype (body weight)

White Pink Red Phenotype color

Phenotype (body weight)

22.6 A frequency distribution is a graph that displays the number or proportion of different phenotypes.

Phenotypic values are plotted on the horizontal axis and the numbers (or proportions) of individuals in each class are plotted on the vertical axis.

symmetrical (bell-shaped) curve called a normal distribution (IFigure 22.7a). Normal distributions arise when a large number of independent factors contribute to a measurement. Quantitative characteristics are frequently affected by numerous genes and environmental factors; so their phenotypes often exhibit normal distributions. Two other common types of distributions (skewed and bimodal) are illustrated in 4 Figure 22.7b and c.

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