Drosophila has a diploid chromosome number of 2n = 8, which includes one pair of sex chromosomes (XX in females and XY in males) and three pairs of autosomes. Consider a Drosophila male that has a copy of the A₁ allele on its X chromosome (the Y chromosome is the homolog) and is heterozygous for alleles B₁ and B₂, C₁ and C₂, and D₁ and D₂ of genes that are each on a different autosomal pair. In the diagrams requested below, indicate the alleles carried on each chromosome and sister chromatid. Assume that no crossover occurs between homologous chromosomes.

What is the genotype of cells produced by mitotic division in this male?

Key Concepts

Diploid and Haploid Cells

Diploid cells contain two complete sets of chromosomes, one from each parent, denoted as 2n. In Drosophila, the diploid number is 8, meaning there are four pairs of chromosomes, including one pair of sex chromosomes. In contrast, haploid cells, such as gametes, have only one set of chromosomes (n). Understanding the diploid nature of Drosophila is crucial for analyzing genetic inheritance and cell division.

Mitosis

Mitosis is the process of cell division that results in two genetically identical daughter cells, each with the same diploid chromosome number as the parent cell. During mitosis, chromosomes are replicated and then evenly distributed to the daughter cells. In the context of the question, the male Drosophila will produce somatic cells through mitosis, maintaining the genotype of the original cell, including the alleles present on the X and autosomal chromosomes.

Alleles and Genotype

Alleles are different versions of a gene that can exist at a specific locus on a chromosome. The genotype refers to the specific alleles an organism carries, which can be homozygous (same alleles) or heterozygous (different alleles). In the case of the Drosophila male described, the genotype includes the A₁ allele on the X chromosome and heterozygous combinations of B₁/B₂, C₁/C₂, and D₁/D₂ on the autosomes, which are essential for determining the genetic makeup of the cells produced by mitosis.