Biology 1001A Lecture Notes - Lecture 11: Wild Type, Genetic Recombination, Melanocyte

• School: Western University
• Department: Biology
• Course: Biology 1001A
• Professor: Tom Haffie

Document Summary

Variation in natural populations: phenotypic traits exhibit either quantitative or qualitative variation within populations, genetic variation, environmental factors, or an interaction between the two cause phenotypic variation within populations. Only genetically based phenotypic variation is heritable and subject to evolutionary change: genetic variation arises within populations largely through mutation and genetic recombination. Artificial selection experiments and analyses of protein and dna sequences reveal that most populations include significant genetic variation: natural selection alters phenotypic variation in three ways. Directional selection increases or decreases the mean value of a trait. Stabilizing selection increases the frequency of the mean phenotype and reduces variability in the trait. Disruptive selection increases the frequencies of extreme phenotypes and decreases the frequency of intermediate phenotypes. Outcomes: three different types of traits can be observed in the phenotype. Respectively the qualitative, the quantitative and the threshold traits: a qualitative trait is expressed qualitatively, which means that the phenotype falls into different categories.