Question

The genes for the eye color and size of the wing in Drosophila are located on the same chromosome. They can be separated/ recombinants develop due to
A. Non-disjunction
B. Crossing over
C. Hybridization
D. Not be separated at any stage

Answer 1

Hint: When the genes are located on the same chromosome but are far apart, they undergo independent assortment which leads to new recombinants.

Complete answer: Recombination is a process by which pieces of DNA are broken and recombined to produce new combinations of alleles.
1. Crossovers result in recombination and the exchange of genetic material between the maternal and paternal chromosomes.
2. The chances of crossing over to occur keep on decreasing with age, and also when the distance between two genes on a chromosome decreases.

The diagram given below shows Morgan’s experimental cross of white-eyes and miniature wings in Drosophila:

3. Recombinants produced due to crossing over can have different combinations of genes than their parents. In his experiments, Thomas Hunt Morgan noticed the deviation in the frequency of recombinant and parental progenies due to the presence of linked genes.
4. Crossing over occurs during the pachytene stage of meiosis I and is a mechanism to break linkage. Both the genes for eye color and size of the wing in the fruit fly Drosophila melanogaster is located on the X chromosome of the fly.
5. It is interesting to note that the recombination of certain linked genes, produced due to the chance event of crossing over, plays a very significant role in evolution.

So, the correct answer is B. Crossing over.

Note: Most of the time recombination occurs naturally; during meiosis in eukaryotes, genetic recombination involves the pairing of homologous chromosomes.