Evolutionary mechanisms. 1. Mutation: the only source of new genetic information. Mutation: any heritable change in the structure or amount of genetic.

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Presentation transcript:

Evolutionary mechanisms

1. Mutation: the only source of new genetic information. Mutation: any heritable change in the structure or amount of genetic material. Different levels of mutation DNA: point and frame shift mutations (mistakes made during DNA replication) Arrangements of DNA +/- of single chromosomes + complete sets of chromosomes. Spontaneous Only mutations occurring during meiosis can affect the next generation.

2. Evolutionary forces: in small populations Natural populations are finite in size. Geographically structured so that mating, within a species, is not random. A. Genetic Drift. Process occurring in small, isolated populations (demes). The frequency of different alleles between generations can fluctuate BY CHANCE. Therefore, by definition, genetic drift is an evolutionary force. But, mutations cannot be anticipated; therefore, cannot reliably produce adaptations.

Dots = demes Geographic distribution of a species

Computer modeling of genetic drift Start with 4 heterozygous individuals (A1/A2)

Example 1 of genetic drift

Desert: 8,000 to 4,000 ybp Contiguous with SW desert Then retreat of deserts to SW Present: oak-hickory forest Relictual populations each with. c.12 lizards.

Example 2 of genetic drift Tristan da Cunha; island; in southern Atlantic; one of most isolated places on earth; administered by Great Britain. 1816: William Glass, wife, two daughters Joined later by a few additional settlers from England 1961: volcano eruption forced removal of all residents (294) In England, tested for various genetic traits. All residents homozygous (alleles fixed) for nine genetic markers. Clinodactyly (dominant) present in the Glass family. Alternative glucose-6-phosphate dehydrogenase allele arrived in 1827…..gene flow.

B. Founder Effect Occurs when a small segment of a population becomes geographically isolated from the larger population The smaller population has only a fraction of the genetic variation of the larger population.

C. Population bottleneck: What does it do?

3. Gene Flow: Individuals carry alleles from one population to another population. Gene flow refers to migration Influenced by culture and social structure. Gene flow (exchange of genes between populations) has increased over time.

4. Natural selection: directional selection

Natural selection: e.g.: Stabilizing selection 19.2 lbs. = c. 8.5 kg