OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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How many chromosomes do sperm or egg cells contain?

46 chromosomes arranged into 23 pairs
26 single chromosomes
23 single chromosomes
20 chromosomes

The correct answer is: 23 single chromosomes

Sperm and egg cells, also known as gametes, each contain 23 single chromosomes. This is referred to as the haploid number, which is half the total number of chromosomes found in somatic (body) cells. In humans, somatic cells typically contain 46 chromosomes arranged as 23 pairs, with each pair consisting of one chromosome inherited from each parent. During the process of meiosis, which produces gametes, the chromosome number is halved to ensure that when fertilization occurs, the resulting zygote has the correct diploid number of chromosomes, 46. This halving is crucial for maintaining the stable chromosome number across generations in sexual reproduction.