During gamete formation, how many alleles from each gene pair are present in a gamete?

• A. Two
• B. Zero
• C. One
• D. Many

Answer: (C)

The main idea is that gamete formation produces haploid cells. Meiosis halves the chromosome number, so each gamete contains one chromosome from each homologous pair. For any given gene, there are two alleles—one on each homolog. When the homologous chromosomes separate in meiosis I, a gamete ends up with just one of those two alleles. The later separation of sister chromatids doesn’t add another allele for that gene, since they carry the same allele. So, a gamete carries one allele for each gene. When fertilization occurs, the zygote gets two alleles for each gene again.