Anthropology notes

Anthropology notes - 22:28:00 ← Forces of evolution • 1...

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Unformatted text preview: 17/10/2007 22:28:00 ← Forces of evolution • 1. Mutation • 2. Genetic drift • 3. Gene flow • 4. Natural selection ← Mutation : change in DNA sequence of a gene due to random error ← Genetic drift : random change in allele frequency ← Gene flow : movement of genes from one population to another ← Natural selection : difference in levels of fitness depending on genotypes or phenotypes ← 1. Mutation: • Source of all new genetic material in a species • Must occur in a gamete to have evolutionary significance • Most mutations have a detrimental effect and are weeded out by natural selection • In some cases, mutations can be advantages • Chromosomal mutation • Monosomy: loss of a chromosome • Trisomy : extra chromosome • Klinefelter’s syndrome : XXY male that’s infertile (a he-she) • Point mutation : substitution of one base for another, which may produce a stop codon : o TTT- T AA-ATA o TTT- G AA-ATA o ACC-TTT-AT A o ACC-TTT-AT T ← 4. Natural selection: • fitness – relative change in the environment can change fitness • Natural selection of simple traits: o Selection against one of the zygotes o Selection for heterozygotes (heterozygote advantage) o Sickle-cell o Genotypes: AA: normal As: reduced oxygen Ss: suffer from Sickle cell anemia o Selection for heterozygotes Balanced polymorphism • Can either increase or decrease variation within population variation • Natural selection is the only evolutionary force that has direct adaptive consequences • It favors useful genes while eliminating deleterious ones • Directional Selection: • (e.g. increase in brain size in humans through time) • selection against one extreme or the other o directional selection o causes a change in the mean • Stabilizing selection: • No major change in mean size • Reduces variation ← • Disruptive selection: • Results in bimodal distribution • Simple (Mendelian) traits: one gene = one trait • Complex traits: polygenic traits o Pleiotropic traits • Pleiotropic Traits: o PKU homozygotes don’t produce enzyme that converts amino acid phenylalanine to tyrosine o Causes CNS damage o Dietary management can prevent damage o Other consequences of PKU: blue eyes, fair skin, light hair, all due to diminished ability to produce melanin. ← Macroevolution • Occurs over many generations and focuses on major biological changes, such as speciation (e.g. homo sapiens) ← Hardy-Weinberg theory: • Mathematical model that predicts the distribution of alleles in a population • Identifies when a population is in genetic equilibrium...
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Anthropology notes - 22:28:00 ← Forces of evolution • 1...

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