Question

In Drosophila flies, red eyes (R) are dominant to white eyes (r) and normal wings (W) are dominant to vestigial wings (w). A scientist performs a test cross by mating a RrWw fly with an arrow fly to produce the following offspring: What is the percent recombination frequency for this cross?

Answer 1

We can analyze the phenotype expressed by each descendant and determine the percentage of recombination frequency.

75 % express red eyes

25 % express white eyes

75 % express normal wings

25 % express vestigial wings

accordingly

6.25 % express white eyes and vestigial wings

Step-by-step explanation:

To make a cross with two genetic variables you must first analyze the possible gametes that can be formed. In this case:

- The eye color phenotype has Rr genotype. You can get two different gametes.

- The wings phenotype presents Ww genotype. You can get two different gametes.

If we analyze all possible gametes with the combination of genotypes we get RW, Rw, rW and rw. Each of the combinations for the two flies that cross is taken to the Punnett square:

cross RW Rw rW rw

RW RRWW RRWw RrWW RrWw

Rw RRWw RRww RrWw Rrww

rW RrWW RrWw rrWW rrWw

rw RrWw Rrww rrWw rrww

The RR and Rr genotypes express the dominant phenotype: red eyes.

The rr genotype expresses the recessive phenotype: white eyes.

The WW and Ww genotypes express the dominant phenotype: normal wings.

The ww genotype expresses the recessive phenotype: vestigial wings.

Answer 2

Incomplete question:

Phenotype----------------------------------Number of offspring

red-eyed, normal wings-------------------368

red-eyed, vestigial wings------------------56

white-eyed, normal wings-----------------40

white-eyed, vestigial wings----------------336

the percent recombination frequency for this cross is 12%

Step-by-step explanation:

The recombination frequency is equal to:

`RF=(number-of-recombinant-progenies)/(total-of-progenies) *100`

The maximum recombination is 50%. It is further observed that the number of white eyes and normal wings and the number of red eyes and vestigial wings are less than the number of normal red eyes and white eye vestigial wings. In this way, it is concluded that the species with white eyes and normal wings and red eyes and vestigial wings are the recombinant progenies.

The recombinant frequency is:

`RF=(40+56)/(800) *100=12`%