A E Crossing over facts, inforr lackboard.albany.edu/bbcswebdav/pid-3088448-dt-c

Question

A E Crossing over facts, inforr lackboard.albany.edu/bbcswebdav/pid-3088448-dt-content-rid-16542330 1/courses/2183-ABIO-212Y-1349 1. Two plants in a cross were each heterozygous for two gene pairs (AB/ab) whose loci are linked and 30 map units (mu) apart. (Recall that 1 mu is equal to 1% recombination between two genes.) Assuming that crossing over occurs during the formation of both male and female gametes and that the A and B alleles are dominant, determine the phenotypic ratio of their offspring. a. What gametes and in what proportions will the individual plants produce? What will be the phenotypic ratio of the offspring from these two plants (both AB/ab)? b. 2. A female has the following genotype: This female produces 100 meiotic tetrads. Of these, 68 show no crossover events. Of the remaining 32, 20 show a crossover between a and b, 10 show a crossover between b a. Assuming the order a-b-c and the allele arrangement shown above, what is the Assuming the order a-b-c and the allele arrangement shown above, what is the and c, and 2 show a double crossover between a and b and between b and c. map distance between a and b loci? b. map distance between b and c loci? 3. Why is crossing over important? F8 F7

Explanation / Answer

1) Both parents (AaBb) produce 25% each of AB, Ab, aB, and ab. phenotypic ratio = 9:3:3:1

2) Given single cross over between a and b = 20

single cross over between b and c = 10

DCO = 2

Map distance = ((number of SCO + DCO)/ number of offspring)*100

Map distance between a and b loci = (22/100)*100 = 22cM

Map distance between b and c loci = (12/100)*100 = 12cM

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