Q.14 Drosophila melanogaster is a diploid organism having 8 chromosomes. The number of
combinations of chromosomes which are possible in its gametes is ____

Drosophila melanogaster, a diploid organism with 8 chromosomes (2n = 8), produces gametes through meiosis where independent assortment generates 16 possible chromosome combinations.​

Chromosome Basics

Drosophila melanogaster has 8 chromosomes in somatic cells, organized as 4 homologous pairs (n = 4): chromosomes 1 (X/Y sex chromosomes), 2, 3, and 4 (dot chromosome). Gametes are haploid, receiving one chromosome from each pair during meiosis I.​​

Independent Assortment Formula

The number of unique gamete chromosome combinations equals 2n2n, where n is the haploid number (4 for Drosophila). For n = 4, 24=1624=16 combinations arise because each pair assort independently—maternal or paternal chromosome can go to either pole with equal probability.​​

Step-by-Step Calculation

Meiosis segregates each of the 4 pairs independently:

• Pair 1: 2 choices (maternal or paternal).

• Pair 2: 2 choices.

• Pair 3: 2 choices.

• Pair 4: 2 choices.
  Total: $2\times 2\times 2\times 2=16$. This excludes crossing over, which adds allelic variation but not new chromosome sets.​

Common Options Explained

• 4: Matches haploid chromosome number (n), not combinations.​

• 8: Equals diploid number (2n); irrelevant for gametes.​

• 16 (correct): 2424 from independent assortment.​

• 256: 2828, if confusing total chromosomes for pairs (common error).​

Drosophila melanogaster gametes chromosome combinations are a key CSIR NET genetics topic for biology students. This diploid organism with 8 chromosomes (2n=8, n=4 pairs) produces exactly 16 possible gamete chromosome combinations through meiotic independent assortment.​

Why 16 Combinations in Drosophila Gametes?

Drosophila melanogaster gametes chromosome combinations follow Mendel’s Law of Independent Assortment. With 4 chromosome pairs, each gamete gets one from each pair, yielding 24=1624=16 variants. No crossing over on chromosome 4, but assortment alone creates diversity.​​

Meiosis Process in Drosophila (2n=8)

• Prophase I: Homologous pairs (chromosomes 1,2,3,4) align.

• Metaphase I: Pairs orient randomly (2 choices per pair).

• Anaphase I: One chromosome per pair to each pole.
  Result: 16 maternal/paternal mixes per gamete.​

CSIR NET Exam Tips

Practice: For any diploid (2n chromosomes), combinations = 2n2n where n=2n/2. Humans (2n=46, n=23): ~8 million. Error trap: Don’t use 2^8=256 (total chromosomes).​