Biology 1001A Chapter Notes - Chapter 18.1: Genetic Variation, Directional Selection, Disruptive Selection
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Even individual that look alive are not identical => variations in weight, biochemistry, physiology, internal anatomy, and behaviour. Phenotypic variation is differences in appearance or function among individuals of a population. If a difference is heritable, it is passed from generation to generation. Quantitative variation is the small, incremental differences between individuals. This data is usually displayed in a bar graph or curve. Natural selection often changes the mean value of a character or its variability within populations. Qualitative variations exist in two or more discrete states and intermediate forms are often absent. The existence of discrete variants of a character is called polymorphism. Phenotypic polymorphisms are qualitatively described in percentage or frequency of that trait. Phenotypic variation within populations may be caused by genetic differences between individuals, by differences in the environmental factors that individuals experience, or (cid:271)(cid:455) a(cid:374) i(cid:374)tera(cid:272)tio(cid:374) (cid:271)et(cid:449)ee(cid:374) a(cid:374) i(cid:374)di(cid:448)idual"s ge(cid:374)eti(cid:272)s a(cid:374)d the e(cid:374)(cid:448)iro(cid:374)(cid:373)e(cid:374)t. Genetic and phenotypic variation may not be perfectly correlated.
