lecture15 - SELECTION Why doesn't selection work anymore on...

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Unformatted text preview: SELECTION Why doesn't selection work anymore on running speed? A) There are probably diseases involved B) Too much inbreeding producing genetic defects C) There is no more genetic variation in the stock D) Epistatic effects are now in play E) Artificial insemination programs inadvertently select for defective (weaker) sperm. In order for Evolution to Occur there must be variation in the population Which is NOT a cause of allele variation in a population? A) Homology B) Mutation C) Genetic recombination (cross over) D) Sexual recombination E) Migration (gene flow) SO Selection & Genetic drift working on variation in the population cause How Effective Is Selection? Consider Artificial Selection In fact, all of these plants Come from wild mustard ! Artificial Selection cont'. 1 Farm animals (e.g. chicken egg production) 126 eggs/hen/year Today 365 eggs/hen/year Artificial Selection in Dogs Dogs All dog fossils from 10,000 years ago are from one species of Asian Wolf The Romans (2,000 yrs ago) had 6 breeds All other breeds have been developed in the last 400 years !!!!! Differences in mortality & reproduction lead NATURAL SELECTION to differences in the proportion of alleles passing to the next generation. Positive selection= a selective advantage for one allele and that favored allele increases in the population. Negative selection= a selective disadvantage for a allele and that tends to disappear from the population. NATURAL SELECTION IN BACTERIA Development of antibiotic resistance in bacteria e.g. NATURAL SELECTION IN BACTERIA Resistance to antibiotics e.g. NATURAL SELECTION IN INSECTS Resistance to pesticides Foliate insecticide NATURAL SELECTION OF PLANTS TO Herbicide Year Deployed Resistance Observed Please look at the video. NATURAL SELECTION IN PLANTS FOR COPPER TOLERENCE WHAT PRODUCES SELECTION? Internal Environment e.g. genetic environment e.g. physiological/developmental environment External Environment Physical Environment (water, temp., 02,) Biological Environment Competition Predation Parasitism Food supply Mate selection (Sexual Selection) Success must be judged in 2 ways: Absolute Terms= Will the genome work? Relative Terms= Is the genome the best available model? Small Selective Advantages How many inches will the nose grow in 100,000 years? A) 1.0 B) 10 C) 100 D) 1000 E) None of the above. Suppose that there were a selective advantage to having a long nose and suppose there was a trend that the average nose length increased 0.001/year SELECTION IN 2 ALLELE TRAITS Selection against a dominant trait Genotypes: AA Aa aa Rapid elimination of the trait should occur. Acondroplastic Dwarfism Caused by dominant allele D Fitness & Natural Selection How to calculate fitness Compare the success of the favored allele to that of the unfavored allele. e.g. Acondroplastic dwarfism (dominant allele) W= number of children produced by 100 dwarfs number of children produced by 100 normals W= 20/100= 0.20 = fitness coefficient for dwarfs Clicker Question If W= 20/100= 0.20 is the fitness coefficient for dwarfs What is the fitness coefficient of the normal individuals? A) Zero B) 0.2 C) 0.5 D) 1.0 E) None of the above Answer Remember that the fitness of the best allele is always = 1.0 Since the normals produce more offspring than the dwarfs, they have a W = 1.0 Dwarfism would rapidly be eliminated from the population if it were not for its high mutation rate! Selection in two allele systems Cont'. Selection against the recessive Genotypes: AA Aa aa Selection will be slow to remove the "a" allele in complete dominance because it is hidden in the heterozygous condition "Aa." These are carriers. Cystic Fibrosis Caused by recessive trait, cc Normal allele C, causes channels in the cell membranes (lung, gut) to allow Cl out of cell H20 follows. If both alleles are cc, then this doesn't happen & thick sticky mucus clogs lungs & gut & these tissues are breeding ground for bacteria Cystic Fibrosis Most common genetic disorder in Caucasians; affects 1 out of 2,500 white babies 5% of Caucasians are carriers CC is normal Cc is normal, but carrier cc has cystic fibrosis Clicker Question A) B) C) D) E) If two carriers have children, what are the chances that their child will have CF? 100% 75% 50% 25% Zero % Cystic Fibrosis Cc x Cc = 25% of kids are cc & have Cystic Fib. Why aren't they eliminated from the pop? Because Cc have protection against diarrhea ? Selection in two allele systems Cont'. Selection favoring heterozygotes "Aa" Can only occur if incomplete or codominance because the trait must be expressed. e.g. Sicklecell anemia Sickle Cell Codominance Normal HbN HbN HbS Mild Anemia Severe Anemia HbN HbS HbS W = 0.14 In the USA: W = 1.0 W = 0.9 In Africa: W = 0.88 W = 1.0 W = 0.14 Heterozygotes are favored in Africa because they are more resistant to malaria! Natural Selection in Polygene Traits Directional Selection Natural Selection in Polygene Traits Stabilizing Selection Natural Selection in Polygene Traits Disruptive Selection Natural Selection in Humans A) B) C) D) E) What kind of selection is this? Directional Stabilizing Disruptive None of the above No way to know ...
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This note was uploaded on 10/08/2009 for the course BIO 200 taught by Professor Herreid during the Fall '07 term at SUNY Buffalo.

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