Secure Assume that three pairs of alleles are found in Droso

Secure Assume that three pairs of alleles are found in Drosophila: x+ and x-, y+ and y-, and z+ and z-. As shown by the symbols, each non-wild-type allele is recessive to its wild-type allele. A cross between female heterozygous at these three loci and wild-type males yields progeny having the following genotypes: x+ y+ z+ females 1010 x- y+ z- males 430 x+ y- z+ males 441, x- y- z- males 39 x+ y+ z- males 32. x+ y+ z+ males 30 x- y- z+ males 27 x+ y- z- male 1 x- y+ z+ male 0 What is the recombinant frequency between x and y? Decimal answer o (wote: there is no crossing over in Drosophila males) 0.1300 are correct. Previous Toles Your receipt no. is 164-2822 What is the recombinant frequency between x and z? Decimal answer only. 0.0600

Solution

The data indicate that the progeny males have a different phenotype than the females. Therefore, all the genes are on the X chromosome. The two most frequent phenotypes in the males (430 x- y+ z-, and 441 x+ y- z+) indicate the genotypes of the X chromosomes in the female, and the two least frequent phenotypes in the males (1 x+ y- z-, and 0 x- y+ z+) indicate the gene order. Gene z is in the middle. Data from only the males are used to determine map distances:

x- z- y+ males 430 Parental

x+ z+ y- males 441 Parental

x- z- y- males 39 Single crossover (SCO) between z-y

x+ z+ y+ males 30 Single crossover (SCO) between z-y

x+ z- y+ males 32 Single crossover (SCO) between x-z

x- z+ y- males 27 Single crossover (SCO) between x-z

x+ z- y- male 1 Double crossover (SCO)

x- z+ y+ male 0 Double crossover (SCO)

Total male progeny = 430 + 441 + 39 + 30 + 32 + 27 +1 = 1,000

z-y = (39+30+1+0)/1,000 = 0.0700 = 7% recombinant frequency= 7 map units

x-z = (32+27+1+0)/1,000 = 0.0600 = 6% recombinant frequency =6 map units

Coefficient of coincidence = Observed number of double crossovers/Expected number of double cross overs = (1+0)/(1,000*0.06*0.07)=0.2380

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