Q1. Source: CSIR NET NOV 20; Session I
Mutation is essential for genetic variation. Which one of the following events can lead to variation amongst the gametes produced by males of Drosophila melanogaster?
[Crossing over does not occur in D. melanogaster males.]
a. Segregation
b. Imprinting
c. Recombination
d. Independent Assortment
Explanation
Genetic variation during meiosis is mainly generated through crossing over and independent assortment.
However, male Drosophila melanogaster do not undergo crossing over during meiosis. Therefore, recombination is absent in male fruit flies.
Despite this, variation is still produced because homologous chromosome pairs align randomly during metaphase I and segregate independently into daughter cells. This process, known as independent assortment, creates different combinations of maternal and paternal chromosomes in the gametes.
Thus, even in the absence of crossing over, independent assortment remains an important source of genetic variation.
Right answer: d. Independent Assortment
Q2. Source: CSIR NET NOV 20; Session I
UV-induced DNA damage causes advancing replication forks to stall. To avoid a collapse of these stalled replication forks the cell uses:
a. Non-Homologous End Joining
b. Lesion Bypass
c. Mismatch Repair
d. Base Excision Repair
Explanation
Ultraviolet (UV) radiation commonly produces thymine dimers and other bulky DNA lesions, which block the progression of DNA polymerase during replication.
To prevent replication forks from collapsing, cells employ lesion bypass, also known as translesion DNA synthesis (TLS). Specialized DNA polymerases temporarily replicate across the damaged DNA, allowing replication to continue. Although this process is more error-prone than normal DNA replication, it helps ensure that the entire genome is duplicated.
The other options are incorrect because:
- Non-Homologous End Joining (NHEJ) repairs double-strand DNA breaks.
- Mismatch Repair (MMR) corrects base-pair mismatches introduced during DNA replication.
- Base Excision Repair (BER) repairs small, non-bulky base lesions such as oxidized or deaminated bases.
Therefore, the correct answer is:
Correct answer: b. Lesion Bypass
Your Score?
🟢 2/2 – Genetics Master!
🟡 1/2 – Great effort! Keep revising.
🔴 0/2 – Time to revisit the fundamentals.
See you next week with another edition of Crack the Question!