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

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How many chromosomes are found in a zygote?

23 pairs
46 single chromosomes
24 pairs
22 pairs

The correct answer is: 23 pairs

A zygote is formed when a sperm cell fertilizes an egg cell, combining their genetic material. In humans, each gamete (sperm or egg) contains 23 chromosomes. Upon fertilization, these two sets of chromosomes merge, resulting in a total of 46 chromosomes in the zygote, which can also be expressed as 23 pairs. Each pair consists of one chromosome from the mother and one from the father, maintaining the diploid state of the organism. The other options present incorrect configurations of chromosome numbers. For instance, while it's true that a zygote has 46 chromosomes, representing 23 pairs, stating it as 46 single chromosomes ignores the pairing nature of the chromosomes, which is fundamental to human genetics. Similarly, stating the number of pairs as 24 or 22 is also inaccurate since they do not reflect the number of chromosomes present in humans. Therefore, the accurate representation is that a zygote contains 23 pairs of chromosomes.