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**Lamarck vs Darwin worksheet Bell Ringer **

Agenda: Early Morning Lab Lamarck vs Darwin worksheet Bell Ringer Notes over Genetic Drift and Hardy Weinberg Hardy Weinberg/Genetic Drift worksheet Objective: I can explain genetic drift and calculate allele frequency using Hardy-Weinberg.

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**In addition to natural selection, evolutionary change is also driven by random processes…**

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II. GENETIC DRIFT The smaller the population, the less genetic variety it has. In a very small population, alleles can be lost from one generation to the next, simply by random chance. When a population evolves only because of this type of random sampling error, GENETIC DRIFT is taking place.

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Genetic Drift Chance events changing frequency of traits in a population not adaptation to environmental conditions not selection founder effect small group splinters off & starts a new colony it’s random who joins the group bottleneck a disaster reduces population to small number & then population recovers & expands again but from a limited gene pool who survives disaster may be random Founders: When a new population is started by only a small group of individuals. Just by chance some rare alleles may be at high frequency; others may be missing; skew the gene pool of new population. Ex: human populations that started from small group of colonists example: colonization of New World Bottleneck: When large population is drastically reduced by a disaster-famine, natural disaster, loss of habitat…loss of variation by chance event alleles lost from gene pool not due to fitness, narrows the gene pool

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FOUNDER EFFECT

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BOTTLENECK EFFECT

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**Ex: Cheetahs All cheetahs share a small number of alleles**

less than 1% diversity 2 bottlenecks 10,000 years ago Ice Age last 100 years poaching & loss of habitat

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Conservation issues Peregrine Falcon Bottlenecking is an important concept in conservation biology of endangered species loss of alleles from gene pool reduces variation reduces adaptability Breeding programs must consciously outcross Golden Lion Tamarin

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**Human Impact on variation**

How do we affect variation in other populations? Artificial selection/Inbreeding Animal breeds Loss of genetic diversity Insecticide usage Overuse of antibiotics resistant bacterial strains

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**Hardy Weinberg: Population Genetics**

Using mathematical approaches to calculate changes in allele frequencies…this is evidence of evolution.

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**Hardy-Weinberg equilibrium**

Hypothetical, non-evolving population preserves allele frequencies natural populations rarely in H-W equilibrium useful model to measure if forces are acting on a population measuring evolutionary change G.H. Hardy (the English mathematician) and W. Weinberg (the German physician) independently worked out the mathematical basis of population genetics in Their formula predicts the expected genotype frequencies using the allele frequencies in a diploid Mendelian population. They were concerned with questions like "what happens to the frequencies of alleles in a population over time?" and "would you expect to see alleles disappear or become more frequent over time?" G.H. Hardy mathematician W. Weinberg physician

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**Evolution of populations**

Evolution = change in allele frequencies in a population hypothetical: what conditions would cause allele frequencies to not change? very large population size (no genetic drift) no migration (no gene flow in or out) no mutation (no genetic change) random mating (no sexual selection) no natural selection (everyone is equally fit) H-W occurs ONLY in non-evolving populations!

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**Populations & gene pools**

Concepts a population is a localized group of interbreeding individuals gene pool is collection of alleles in the population remember difference between alleles & genes! allele frequency is how common is that allele in the population how many A vs. a in whole population

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**H-W formulas Alleles: p + q = 1 Individuals: p2 + 2pq + q2 = 1 B b BB**

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**Origin of the Equation p2 + 2pq + q2**

Assuming that a trait is recessive or dominant Allele pairs AA, Aa, aa would exist in a population p + q = 1 The probability that an individual would contribute an A is called p The probability that an individual would contribute an a is called q Because only A and a are present in the population the probability that an individual would donate one or the other is 100% p2 + 2pq + q2 Male Gametes A(p) Male Gametes a(q) Female gametes A(p) AA p2 Aa pq Female Gametes a(q) aa q2

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**Hardy-Weinberg theorem**

Frequencies are usually written as decimals! Counting Alleles assume 2 alleles = B, b frequency of dominant allele (B) = p frequency of recessive allele (b) = q frequencies must add to 1 (100%), so: p + q = 1 BB Bb bb

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**Hardy-Weinberg theorem**

Counting Individuals frequency of homozygous dominant: p x p = p2 frequency of homozygous recessive: q x q = q2 frequency of heterozygotes: (p x q) + (q x p) = 2pq frequencies of all individuals must add to 1 (100%), so: p2 + 2pq + q2 = 1 BB Bb bb

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Practice Problem: In a population of 100 cats, there are 16 white ones. White fur is recessive to black. What are the frequencies of the genotypes?

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**Use Hardy-Weinberg equation!**

q2 (bb): 16/100 = .16 q (b): √.16 = 0.4 p (B): = 0.6 p2=.36 2pq=.48 q2=.16 BB Bb bb Must assume population is in H-W equilibrium! What are the genotype frequencies?

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**Answers: Assuming H-W equilibrium: Expected data Observed data**

2pq=.48 q2=.16 Assuming H-W equilibrium: Expected data BB Bb bb p2=.20 p2=.74 2pq=.10 2pq=.64 q2=.16 q2=.16 Sampled data 1: Hybrids are in some way weaker. Immigration in from an external population that is predomiantly homozygous B Non-random mating... white cats tend to mate with white cats and black cats tend to mate with black cats. Sampled data 2: Heterozygote advantage. What’s preventing this population from being in equilibrium. bb Bb BB Observed data How do you explain the data? How do you explain the data?

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**Tips for Solving HW Problems:**

Solve for q first. Then solve for p. Don’t assume you can just solve for p2 if only given dominant phenotypic frequency. READ carefully!!!

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