An organism has alleles R₁ and R₂ on one pair of homologous chromosomes, and it has alleles  T₁ and T₂  on another pair. Diagram these pairs of homologs at the end of metaphase I, the end of telophase I, and the end of telophase II, and show how meiosis in this organism produces gametes in expected Mendelian proportions. Assume no crossover between homologous chromosomes.

Key Concepts

Homologous Chromosomes

Homologous chromosomes are pairs of chromosomes in a diploid organism that have the same structure and gene sequence but may carry different alleles. Each parent contributes one chromosome to the pair, resulting in two copies of each gene. During meiosis, these chromosomes segregate to ensure that gametes receive only one allele from each pair, which is crucial for understanding genetic variation in offspring.

Meiosis Stages

Meiosis consists of two rounds of cell division: meiosis I and meiosis II. In meiosis I, homologous chromosomes are separated, while in meiosis II, sister chromatids are separated. At the end of metaphase I, homologs align at the equatorial plane, and by the end of telophase II, four haploid gametes are produced, each containing a unique combination of alleles due to independent assortment.

Mendelian Proportions

Mendelian proportions refer to the predictable ratios of genotypes and phenotypes in offspring resulting from genetic crosses, as described by Gregor Mendel's laws of inheritance. In this case, the alleles R₁, R₂, T₁, and T₂ will assort independently during meiosis, leading to gametes that can combine in various ways, typically resulting in a 1:2:1 ratio for heterozygous crosses and a 9:3:3:1 ratio for dihybrid crosses.