Handout 9 (part 1 &2)

Handout 9 (part 1 &2) - Handout 9 Warm-up problems...

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Handout 9 Warm-up problems: 1. T/F A two-point testcross is more accurate than a three point testcross ( false, 2 point testcrosses usually miss out double crossing over while 3 point testcrosses often detect double crossover. 3 point testcrosses also determine order of genes.) 2. T/ F Mapping experiments become more accurate as the distance between genes increases. ( false, higher chance of DCO and other CO that might be missed in calculation) 3. T/F The higher the coefficient of coincidence, the higher the degree of crossover interference. (false, the opposite. The interference is the degree to which one crossover interferes with additional crossovers in the same region. C.O.C indicates % DCO in progeny actually observed while interference is % DCO in progeny actually not observed) 4. a-b = 50%, a-c = 50%, a-d = 50%, b-c = 20%, b-d =10%, c-d = 28% Ans: Linkage 1 ---------------------a------------------------------------------------ Linkage 2 ----------------d------b----------------------------------c---------- 5. In pea plants, the peas can be either rough or smooth, and either soft or hard. You do some crosses and obtain the following results. Cross 1: purebred rough, soft pea X purebred smooth, hard pea. Gives F1: all rough, hard. Cross 2: rough, hard F1 X smooth, soft ( note: test cross, NOT self cross). Gives F2: 115 rough soft, 110 smooth hard, 8 rough hard, 12 smooth soft. a) Using letters of your own choosing, determine which trait is dominant, which is recessive Let R = rough (dominant), r = smooth (recessive); Let H = hard (dominant), h = soft (recessive) b) Are the genes for roughness and softness linked? Determine what type of linkage is it? Not ratio 1:1:1:1 for testcross of dihybrid -> not independent assortment like Mendelian crosses. Parental types > nonparental (recombinant) types, therefore, YES they are linked. Not complete/ perfect linkage because ratio is not 1:1. c) State the genotypes of the parents, the F1, and each phenotypic class in the F2. Rh/Rh x rH/rH F1 are dihybrids: Rh/rH which are crossed to the tester strain rh/rh F2 are therefore RH/rh rough hard (the gamete from the F1 is RH) nonparental rH/rh smooth hard (the gamete from the F1 is rH) parental Rh/rh rough soft (the gamete from the F1 is Rh) parental Rh/rh smooth soft (the gamete from the F1 is rh) nonparental d) which F2 progeny inherited parental type gametes from the F1 parent, and which nonparental type? e) What is the recombination frequency (distance in centimorgans) between the genes? r.f. = # recombinants x100 = 8+12 x100 = 8.2% rf = 8.2 cM total 8+12+112+110 6. An individual has the genotype Ab/aB (A and b are on one homologous chromosome while a and B are on the other homologous chromosome). Gene loci A and B are 14 cM apart. Testcross is performed on this individual. a. Indicate whether the genotype of the progeny is parental (P) or non-parental (NP). b. percentages of the expected progeny's
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Handout 9 (part 1 &2) - Handout 9 Warm-up problems...

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