BILD 3 Lecture Notes

BILD 3 Lecture Notes - BILD 3 Lecture Notes 10-13-09...

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Unformatted text preview: BILD 3 Lecture Notes 10-13-09 13/10/2009 15:09:00 ← ← Species : group whose members have the potential to interbreed in nature and produce viable offspring. ← Population : group of individuals of the same species that live in the same area and interbreed. ← Probability : formal study of the laws of chance. (Punnett square?) ← ← Hardy-Weinberg Equilibrium Principle: • What would the genetic composition of a population be if that population were not evolving? = Null model, basis for comparison. Gene : functional unit of heredity Allele : alternative forms of genes Locus : location of chromosome Example: A diploid population, sexually reproducing, 2 possible alleles at a locus (A1, A2) Homozygote : Same 2 alleles at a locus: (AA) Heterozygote : Different 2 alleles: (Aa) Gametes : egg & sperm are haploid 1. We have a population of alleles and can calculate their genotype frequencies. A frequency = p a frequency = q p + q = 1 2. Sample alleles, frequency: p=0.7, q= 0.3 AA + Aa + aa = p 2 + 2pq + q 2 Question: 2 x 0.8 x 0.2 = 0.32 Principles: 1. If the allele frequencies are p and q, genotype frequencies will be p 2 , 2pq, and q 2 . 2. The allele frequencies will not change if population does not change. Example: deck of cards shuffled. Null Model based on assumptions: 1. No selection 2. Mating is random 3. Population large enough to be unaffected by chance events 4. No gene flow 5. No mutation ← ← Null Model is rarely met. ← ← Question: What if frequency of homozygotes is higher than expected, given H- W? ← ← Assortative mating? (Non-random) ← ← Is a population in Hardy-Weinberg equilibrium at a particular locus? ← 1. know # genotypes ← 2. calculate # each allele ← 3. calculate allele frequencies ← 4. calculate expected genotype frequencies using H-W ← 5. compare expected vs. observed ← 6. conclusion ← ←----- Read book, learn how to follow equilibrium model!! ← ← Is a population in Hardy-Weinberg equilibrium? ← HLA genes (Human …?) • Immune system, recognize invading organism • Numerous alleles in human population • Alleles – co-dominant • Proteins from different alleles recognize different invaders ← Hypothesis: heterozygotes have fitness advantage Test – is population in H-W equilibrium at these loci? Data – Havaspai tribe, Arizona Do HLA genotype frequencies of humans conform to H-W model?...
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This note was uploaded on 02/21/2010 for the course BILD 3 taught by Professor Wills during the Fall '07 term at UCSD.

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BILD 3 Lecture Notes - BILD 3 Lecture Notes 10-13-09...

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