The drosophila alleles for black body (instead of the normal tan color, which is

Question

The drosophila alleles for black body (instead of the normal tan color, which is the wild type) and curved wings (instead of the wild-type straight wings) are both recessive and on chromosome 2. Gene “C” designates color, with alleles C representing the dominant tan allele and c representing the recessive black allele, while gene “W” designates the wing shape gene with W being the dominant straight allele and w the recessive curved allele. You need to discover how close together these two genes are on chromosome 2. You place one male from a pure breeding stock and one female from a pure breeding stock (these are the ‘parental’ or ‘generation zero’ (G0) flies) into vial 1. The offspring of this cross (cross 1) hatch in vial 1. These offspring (Generation 1, G1) are heterozygous for both genes. You perform the cross from the above question and get 500 offspring in vial 2 (these are the G2 flies). Among these G2 flies, 65 have tan bodies and curved wings, 70 have black bodies and straight wings, 190 have black bodies and curved wings, and 175 have tan bodies and straight wings. What are the genotypes of offspring with parental phenotypes? What are the genotypes of the recombinant offspring?  wo true breeding parents (G0) gave rise to the doubly heterozygous (G1) flies in vial 1. What were the genotypes of these parents?  What is the percent of recombinants for these two genes?  If the two genes were actually on different chromosomes, what phenotypic distribution would you expect in the G2 flies (instead of 65 tan curved, 70 black straight, 190 black curved, and 175 tan straight)?  If the two genes were actually on different chromosomes and you crossed the heterozygous flies to each other (did a self cross) what phenotypic distribution would you expect from the offspring?

Explanation / Answer

The drosophila alleles for black body (instead of the normal tan color, which is the wild type) and curved wings (instead of the wild-type straight wings) are both recessive and on chromosome 2.You place one male from a pure breeding stock and one female from a pure breeding stock (these are the ‘parental’ or ‘generation zero’ (G0) flies) into vial 1.

G0 or Parental generation:      BBWW    X    bbww

These offspring (Generation 1, G1) are heterozygous for both genes.

G1 or offspring genotype:       BbWw

G2 generation:

Genotype of offspring with parental phenotype: BBWW, BbWW, BBWw, BbWw

genotypes of the recombinant offspring: bbWW, bbWw, BBww, Bbww,bbww

the percent of recombinants for these two genes:

Number of recombinants= 65+70+190= 325

total number of offsprings: =65+70+190+175=500

So, percent of recombinants for these two genes= (325/500)* 100 = 65 %

If the two genes were actually on different chromosomes, then the phenotypic distribution we would expect in the G2 flies (instead of 65 tan curved, 70 black straight, 190 black curved, and 175 tan straight) would have followed the classic ratio thaat is 9:3:3:1

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