Exam 3 - Exam 3 We can trace all of life to a single...

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Exam 3 We can trace all of life to a single origin. Natural selection provides the primary mechanism for this phenomenon Homology: shared similarity due to common descent in some ancestral species with modification Structural homology: similarity of morphological traits such as same general limb structure in vertebrates. Product of descent with modification Developmental homology: similarity in embryo morphology and/or pattern of tissue traits that get modified in development so that they don’t show up later. (Mammalian order of primates, ancestrally they have a tail and we and apes don’t, but our early development does have a tail, it just disappears later on) Genetic homology: compare proteins and underlying genetic DNA. Similarity in DNA sequences of genes from different species. Results in developmental homology and structural homology Evolutionary perspective: one common origin for all of life on the planet. All life uses same codon to specify for same amino acids, use ribosomes to make proteins Darwin’s theory of evolution by natural selection was complemented by Mendel’s theory of genetics. Modern evolutionary synthesis: genetic variation (necessary before any selective force can be applied to a population) arises through random, spontaneous mutation. Sexual production continually provides more and more combinations of variations. Changes in allelic frequencies between generations results from genetic drift, gene flow, natural selection. Speciation, start with one species and end up with to two. Populations are reproductive and physically and sexually isolated Selection can maintain genetic variation in a population. Heterozygote advantage: heterozygote genotype has higher fitness than homozygous genotypes (Sickle-Cell anemia) Balancing Selection: heterozygote with the higher fitness is balanced by lower fitness of both of the homozygotes Directional Selection: natural selection increases the frequency of one allele. Reduces population genetic diversity over time. If this goes on for a long time, the favored alleles reach a frequency of 1 (fixed), and the ones no longer found are lost. Selective forces working against individuals of a certain phenotype. Polygenic: multiple loci, multiple genes each with multiple alleles that are going to control the phenotype. (for skin color, darker color helps burn prevention and hence mutations) Directional selection in dog breeding, plants, and cliff swallows. After one selective event in cliff swallows, only the bigger birds survived. (selective event=6 day cold snap) Mice have learned how to predate on Albatross chicks because of the way that seabirds raise young. Young are raised alone on end because they were raised in absence of terrestrial predators. Mice have grown in size since their arrival and have become carnivorous (from vegetarians). Killing many birds because their original food is absent, traits become more accentuated. Stabilizing selection: Individuals with the intermediate traits reproduce more than others, thereby maintaining
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Exam 3 - Exam 3 We can trace all of life to a single...

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