Question

Use the preamble below to answer Questions 27 and 28
In the fruit fly Drosophila melanogaster, red eye colour (R) is dominant to white eye colour (r). A
student wishes to perform a test cross to determine whether a female red eyed fruit fly is
homozygous or heterozygous for the eye colour. The student mates the female fruit fly with a red
eye coloured male and studies the offspring, which are 100% red eye. The student concludes that
the genotype of the female fruit fly Drosophila melanogaster is "RR".
27. What mistake(s) did the student make if any? Briefly explain in bullet points. [5 Marks]
28. Suggest the best way by which a breeder could successfully maintain a supply of red eye
Drosophila melanogaster of the variety that is heterozygous for eye colour. [5 Marks]
Use the preamble below to answer Questions 29 and 30
In a breed of cattle, rough coat is dominant over smooth, and black coat is codominant to red. What
do the following statements mean?
29. The loci of the two pair of genes concerned are on the same pair of chromosomes (assuming
no crossing over). [5 Marks]
30. The loci of the two pair of genes concerned are on different pairs of chromosomes.
[5 Marks]

Answer 1

27. The students should confirm that the male candidate of drosophila melanogaster is heterozygous or homozygous in its genotype for eye color. The male drosophila melanogaster with red eye color may mave RR or Rr genotype. The students should use Rr genotype for crossing because this heterozygous genotype will give the half population of white eye colored progeny when the female drosophila melanogaster is heterozygous. Also if the male drosophila melanogaster has RR genotype than the female drosophila melanogaster with RR or Rr genotype will give 100% red eye population.

28. The breeder should use the homozygous white eye coloured female drosophila melanogaster and homozygous red eye coloured male drosophila melanogaster for their crossings. The homozygous RR drosophila melanogaster can be selected after doing F1 and F2 crossings between the progeny of heterozygous red eye colour drosophila melanogasters.

29. If The loci of the two phylogenetic traits are present on the same chromosome, then they are linked traits to some extent. this means that passing of one trait will take other trait too with it. It occurs when they are present near to each other.

30. When the loci of the two traits are on different chromosomes, than they are independent of each other . That is they are not linked and are using the principle of independent assortment.