2020–2021 BCSC Basic and Clinical Science Course™
2 Fundamentals and Principles of Ophthalmology
Part III: Genetics
Chapter 6: Clinical Genetics
Genes and Chromosomes
In contrast to mitosis, meiosis leads to the production of cells that have only 1 member of each chromosome pair (Fig 6-5). The specialized cells that arise from meiosis and participate in sexual reproduction are called gametes. The male gamete is a sperm, and the female gamete, an ovum. During meiosis, a modified sequence of divisions systematically reduces the number of chromosomes in each cell by one-half to the haploid number. Consequently, each gamete contains 23 chromosomes, 1 representative of each pair. This assortment occurs randomly, except that 1 representative of each pair of chromosomes is incorporated into each sperm or egg.
At conception, a sperm and an ovum unite, forming a zygote, a single cell that contains 46 chromosomes. Because both parents contribute equally to the genetic makeup of their offspring, new and often advantageous gene combinations may emerge.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.