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Sickle Cell Anemia Incomplete Dominance Sex linked traits Multiple Alleles All chicken have combs on their heads, but it does not always look the same. The comb is a fleshy growth on the top of the chicken's head. Both male and female chickens have combs, but the ones on the male are larger. Combs of different breeds may look different in shape and even in color. Chicken comb features: rrpp = single rrP_ = pea R_pp = rose R_P_ = walnut 1. What must be the genotypes of the two parents for the outcome to always be a walnut offspring? (neither can be walnut to begin with) ____________ x _____________ = walnut (R_P_) 2. Show a Punnett square for the following cross and describe the phenotypic ratios. RrPp x RrPp 3. Show a punnett square for the following cross and describe the phenotypic ratios. rrpp x RrPp 4. Show a punnett square for the following cross and describe the phenotypic ratios. rrpp x rrPp 5. A rose crossed with a pea produces six walnut and five rose offspring. What must be the genotypes of the parents? Show the cross. Hardy-Weinberg Principle • Natural selection acts on individuals, but only populations evolve • Explain this statement Hardy-Weinberg Principle • Describes a non-evolving population • The gene pool does not change – Gene pool - all alleles for all loci in the population – Allele frequencies remain constant in nonevolving populations • Why do this? Allelic variation within a population can be modeled by the HardyWeinberg equations. A Population in Hardy-Weinberg Equilibrium http://zoology.okstate.edu/zoo_lrc/biol1114/tutorials/Flash/life4e_15-6-OSU.swf The seven assumptions underlying Hardy–Weinberg equilibrium are as follows: 1. 2. 3. 4. 5. 6. 7. organisms are diploid only sexual reproduction occurs generations are non overlapping mating is random population size is infinitely large allele frequencies are equal in the sexes there is no migration, mutation or selection Fig. 23-6 Interpretation: A population with 80% dominant and 20% recessive alleles that meets the conditions for Hardy-Weinberg equilibrium will pass 80% dominant and 20% recessive alleles to the next generation Alleles in the population Frequencies of alleles p = frequency of CR allele = 0.8 q = frequency of CW allele = 0.2 Gametes produced Each egg: Each sperm: 80% 20% chance chance 80% 20% chance chance Hardy-Weinberg equations: - p+q=1 - p2 + 2pq + q2 = 1 - Describes alleles in a gene pool - This is the equation for a trait with 2 alleles - Can be used to predict genotypes - p – represents dominant allele q – represents the recessive allele • Worksheet 3, 4 and 5 80% CR (p = 0.8) 20% CW (q = 0.2) Worksheet: #6 Sperm CR (80%) CW (20%) 64% (p2) CRCR 16% (pq) CRCW 16% (qp) CRCW 4% (q2) CW CW 64% CRCR, 32% CRCW, and 4% CWCW Gametes of this generation: 64% CR + 16% CR = 80% CR = 0.8 = p 4% CW + 16% CW = 20% CW = 0.2 = q Genotypes in the next generation: 64% CRCR, 32% CRCW, and 4% CWCW plants Reality • Hardy-Weinberg - hypothetical population • In real populations, allele and genotype frequencies change over time You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following: A. What is the frequency of the "aa" genotype in the population? B. What is the allele frequency of the "a" allele? The winged trait is dominant. C. What is the frequency of the "A" allele in the population? D. What is the frequencies of the genotype "Aa” in the population? E. What is the frequencies of the two possible phenotypes if "A" is completely dominant over "a."