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

Why are gametes genetically different from each other?

1. Because of mutations

2. Because of environmental factors

3. Due to random assortment and crossing over

4. Due to parental influences

The correct answer is: Due to random assortment and crossing over

Gametes are genetically different from each other primarily due to the processes of random assortment and crossing over during meiosis. Meiosis is the type of cell division that produces gametes—sperm and eggs—in sexually reproducing organisms. During prophase I of meiosis, homologous chromosomes pair up and can exchange segments of genetic material through a process called crossing over or recombination. This leads to new combinations of alleles on the chromosomes. Additionally, during metaphase I, the orientation of these homologous chromosome pairs is random, which means that the gametes can inherit different combinations of maternal and paternal chromosomes. This random assortment combined with crossing over results in a high level of genetic variation among the gametes. This genetic diversity is crucial for evolution and adaptation, as it increases the chances that some individuals within a population will have traits that suit them to changing environments. Other factors, like mutations or environmental influences, do not account for the systematic genetic differences seen in gametes produced during meiosis. Parental influences are also not a mechanism for the genetic variation seen in gametes, as they refer to the traits inherited by offspring but do not contribute directly to the genetic uniqueness of each gamete.