Understanding Chromosome Numbers in Fruit Flies

This question asks about the chromosome number in the gamete of a fruit fly, given the chromosome number in its meiocyte. To answer this, we need to understand the process of cell division that produces gametes.

In sexually reproducing organisms, gametes (like sperm and egg cells) are produced through a special type of cell division called meiosis. Meiosis is a reductional division, meaning it reduces the number of chromosomes by half.

A meiocyte is a cell that is destined to undergo meiosis. Meiocytes are typically diploid cells, meaning they contain two sets of chromosomes (represented as \(\text{2n}\)). One set comes from each parent.

Gametes, on the other hand, are haploid cells. They contain only one set of chromosomes (represented as \(\text{n}\)). When a male gamete (sperm) fuses with a female gamete (egg) during fertilization, the resulting zygote is diploid (\(\text{2n}\)), restoring the original chromosome number.

Applying the Concept to the Fruit Fly

The question states that the meiocyte of the fruit fly has 8 chromosomes. Since the meiocyte is a diploid cell, its chromosome number is \(\text{2n}\).

So, for the fruit fly:

• Diploid number (\(\text{2n}\)) = 8 chromosomes

Gametes are produced from meiocytes through meiosis, which halves the chromosome number. The chromosome number in a gamete is the haploid number (\(\text{n}\)).

To find the haploid number (\(\text{n}\)), we divide the diploid number (\(\text{2n}\)) by 2:

\(\text{n} = \frac{\text{2n}}{2}\)

Substituting the given value:

\(\text{n} = \frac{8}{2}\)

\(\text{n} = 4\)

Therefore, the chromosome number in the gamete of a fruit fly is 4.

Summary of Chromosome Numbers

Final Answer Derivation

Given that the meiocyte has 8 chromosomes (\(\text{2n} = 8\)), the gamete, which is haploid (\(\text{n}\)), will have half the number of chromosomes. Thus, the chromosome number in the gamete is \(8 / 2 = 4\).

Revision Table: Fruit Fly Chromosomes

Additional Information: Ploidy and Meiosis

Ploidy: Ploidy refers to the number of sets of chromosomes in a cell. Diploid (\(\text{2n}\)) cells have two sets, while haploid (\(\text{n}\)) cells have one set. Most somatic (body) cells in organisms are diploid.

Meiosis: Meiosis is essential for sexual reproduction. It consists of two rounds of division: Meiosis I and Meiosis II.

• Meiosis I: Homologous chromosomes pair up and then separate, reducing the chromosome number by half. This is where the cell goes from diploid (\(\text{2n}\)) to haploid (\(\text{n}\)).
• Meiosis II: Sister chromatids separate, similar to mitosis. The number of chromosomes remains the same (\(\text{n}\)).

The outcome of meiosis is four genetically distinct haploid cells (gametes) from a single diploid meiocyte. This reduction in chromosome number ensures that when two gametes fuse during fertilization, the correct diploid number for the species is restored in the offspring.

Fruit flies (\(\textit{Drosophila melanogaster}\)) are often used in genetics research because they reproduce quickly and have easily observable traits and chromosomes.