BIOL 103 Lecture Notes - Frequency-Dependent Selection, Natural Selection, Gel Electrophoresis Of Proteins
Document Summary
Genetic variation in populations is caused by: mutation (e. g. uv light hitting skin cells) Changes in dna sequences new alleles. Cannot enter population unless in gametes: sexual reproduction variable gametes. Meiosis shuffles maternal and paternal chromosomes into new combinations. Crossing over shuffles alleles into new combinations on each chromosome. Result is genetic and phenotypic variation even in absences of new mutations. Shuffling of homologous chromosomes and crossing over in meiosis leads to new gene combinations and variable gametes. The persistence of sexual reproduction in natural populations unsolved problems for evolutionary biology. In theory: male-producing, sexual populations are subject to invasion and rapid replacement by clonal females. Population of one million sexual individuals would be replaced in less than. 50 generation by a clone beginning with a single asexual female. New molecular techniques in 1960"s showed large amounts of genetic variation: new techniques such as protein electrophoresis revealed more variation than expected; excess variation = genetic load, genetic polymorphism maintained by: