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1 Darwin: Evolution is ____________ _____________________________ Evolution: changes through time 1.Species ____________ difference 2.Descendants ____________ from their ancestors 3.New species ____________ from existing ones Genes Within Populations Chapter 20

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2 Darwin’s natural selection: ____________ a result of preexisting ____________ ____________ Natural selection: mechanism of evolutionary change Darwin’s theory for how long necks evolved in giraffes

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Populations evolve One species, two populations Natural selection acts on individuals –differential ____________ –Differential ____________ ____________ Populations evolve –____________makeup of population ____________ over time –___________________ (greater fitness) become ____________ ____________

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Brief Terminology Review Gene – determines a ____________ (eye color) Allele – A ____________of a ____________ (ex. brown eyes vs. blue eyes) ____________________________ organisms ________2 ____________for any trait. Dominant – An allele that ____________a trait, regardless of the other other allele (ex. brown eyes) Recessive – An allele that _________________ ___________a trait _____________________ ________________ (ex. blue eyes)

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Terminology Review Continued Homozygous – any individual who has 2 ____________________________________ _. _________homozygous _________________or homozygous ______________. Heterozygous- any individual who has ______copy of __________________ __________ copy of a ____________ ____________. WILL SHOW THE ________________ TRAIT!

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Populations & gene pools Concepts –a ______________is a localized group of interbreeding individuals –______________ is _______________ __________________ in the population remember difference between ____________& _______________! –__________________________is how common is that allele in the population how many B vs. b in whole population

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7 STATES: The original proportions of the genotypes in a population will remain constant from generation to generation as long as five assumptions are met The Hardy-Weinberg Principle Five assumptions : 1.No _______________ takes place 2.No _________are _______________ ____or ____________ other sources 3._______________ _________ is occurring 4.The _______________ size is very _______ 5._____________________ occurs

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8 Calculate genotype frequencies: p 2 + 2pq + q 2 = 1 p 2 = individuals _____________________ for _____________________ allele (p) 2pq = individuals _____________________ for both alleles q 2 = individuals _____________________ for _____________________ allele (q) because there are only two alleles: p +q = 1 Hardy-Weinberg Principle

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9 In a population of Cats, Black (B ≈ p) is dominant to White fur (b ≈ q) in Hardy Weinberg equilibrium the frequency of the Black allele is.7 (p =.7). USE 2 equations: p 2 + 2pq + q 2 = 1 AND p +q = 1 a. What is the frequency of the white allele (q)? (remember p + q = 1) p =.7 so.7 +q = ____ solve for q q = ____ b.What is the frequency of homozygous black cats? (p 2 )? p =.7 so p 2 = (___) = _____ c.What is the frequency of the heterozygous cats? (2pq) p =.7 and q =.3 so ___ (___)(___) =._____ Applying the Hardy-Weinberg Principle- check your HW

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10 Using Hardy-Weinberg equation to __________ frequencies in subsequent generations Hardy-Weinberg Principle

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11 In certain Native American groups, albinism due to a homozygous recessive condition in the biochemical pathway for melanin is sometimes seen. If the frequency of the allele for this condition is 0.06, which of the following is closest to the frequency of the dominant allele in this population? (Assume that the population is in Hardy ‑ Weinberg equilibrium.) 1. We are given 0.06, what is this? p, p 2, q q 2, OR 2pq? 2. The question asks for frequency of dominant allele, what is this? p, p 2, q q 2, OR 2pq? 3. Once you figure this out you USE 2 equations: p 2 + 2pq + q 2 = 1 AND p +q = 1 Applying the Hardy-Weinberg Principle- Try another

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