Question

In Drosophila, two mutations, Stubble(Sb) and curled(cu), are linked on chromosome lll. Stubble is a dominant gene that is lethal in a homozygous state, abd curled is a recessive gene.

female: Sb cu / + +
male: + cu / + cu
if the cross is made, and if Sb and cu are 8.2 map units apart on chromosome lll, and is 1000 offspring were recovered,
a) how many ofspring would have stubble bristles and curled wings?
b) how many offspring would have stubble bristles and normal wing?
c) how manu offspring would have curled wings and normal bristles?
please show work.

Answer 1

For the Drosophila:

• a) 164 offspring would have stubble bristles and curled wings.
• b) 250 offspring would have stubble bristles and normal wings.
• c) 250 offspring would have curled wings and normal bristles.

How to determine offspring?

Given:

Female genotype: Sb cu / + + (stubble, curled, heterozygous for both)

Male genotype: + cu / + cu (normal bristles, curled wings, heterozygous for curled)

Linkage distance between Sb and cu: 8.2 map units

Total offspring: 1000

a) Offspring with stubble bristles and curled wings:

Calculate the recombinant frequency (RF) based on the linkage distance:

RF = 8.2 map units / 100 map units

= 0.082

Use the RF to calculate the percentage of double crossover offspring (those with both stubble and curled due to recombination):

2 × RF = 2 × 0.082

= 0.164

Multiply the percentage by the total offspring to get the number of offspring with stubble and curled wings:

0.164 × 1000 = 164

b) Offspring with stubble bristles and normal wings:

Consider that stubble is dominant and normal is recessive. Half of the offspring will inherit the + allele from the male parent, resulting in normal wings.

Among the offspring with the + allele, half will inherit the Sb allele from the mother, resulting in stubble bristles.

Therefore, the percentage of offspring with stubble and normal wings is:

50% (half from the male) × 50% (half with Sb allele) = 25%

Multiply the percentage by the total offspring to get the number of offspring with stubble and normal wings:

0.25 × 1000 = 250

c) Offspring with curled wings and normal bristles:

Similarly, consider that curled is recessive and normal is dominant. Half of the offspring will inherit the + allele from the male parent, resulting in normal bristles.

Among the offspring with the + allele, half will inherit the cu allele from the mother, resulting in curled wings.

Therefore, the percentage of offspring with curled and normal wings is:

50% (half from the male) × 50% (half with cu allele) = 25%

Multiply the percentage by the total offspring to get the number of offspring with curled and normal wings:

0.25 × 1000 = 250