Biology 1001A Chapter Notes - Chapter 18: Snow Goose, Stabilizing Selection, Directional Selection

• School: Western University
• Department: Biology
• Course: Biology 1001A
• Professor: Beth Mac Dougall Shackleton Tom Haffie

Document Summary

Snow geese, have either blue or white feathers, no pale blue: these t(cid:396)aits a(cid:396)e (cid:272)o(cid:374)side(cid:396)ed (cid:862)polymorphic(cid:863, polymorphism - the existence of discrete variants of a character among individuals in a population, ex. Human blood types a, b, ab, and o are also polymorphic: sources of phenotypic variation, and which of these is/are heritable, phenotypic variation - differences in appearance or function between individual organisms. In other words, natural selection operates on the phenotype, not the genotype. Increases genetic variability: how each of the above modes of selection affects phenotypic variation in a population. Directional: a populatio(cid:374)"s ge(cid:374)eti(cid:272) (cid:448)a(cid:396)iatio(cid:374) shifts to(cid:449)a(cid:396)ds the e(cid:374)d/e(cid:454)t(cid:396)e(cid:373)e of the phe(cid:374)ot(cid:455)pi(cid:272) spe(cid:272)t(cid:396)u(cid:373, this may reduce the variability in the trait. Stabilizing: a populatio(cid:374)"s ge(cid:374)eti(cid:272) (cid:448)a(cid:396)iatio(cid:374) is shifted to the i(cid:374)te(cid:396)(cid:373)ediate phe(cid:374)ot(cid:455)pes (cid:271)(cid:455) eli(cid:373)i(cid:374)ati(cid:374)g the phenotypic extremes, this reduces genetic and phenotypic variation, but increases the frequency of intermediate phenotypes.