Sexual reproduction relies on a specialized cell division process called meiosis. This process reduces the chromosome number in gametes (sperm and egg cells) by half. For example, in humans, diploid cells with 46 chromosomes undergo meiosis to produce haploid gametes with 23 chromosomes each. This reduction is essential because fertilization, the fusion of two gametes, restores the full diploid chromosome complement. The halved chromosome number in gametes is evident through microscopic examination of the cells during the different stages of meiosis, revealing the separation of homologous chromosomes and the formation of haploid daughter cells.
Maintaining the correct chromosome number across generations is crucial for the viability and proper development of offspring. Errors in meiosis, leading to an abnormal chromosome number in gametes, can result in conditions such as Down syndrome. The understanding of meiotic chromosome reduction has been fundamental to advancements in genetics, reproductive medicine, and evolutionary biology. Historically, observing the behavior of chromosomes during meiosis provided critical evidence for the chromosome theory of inheritance.
