2020–2021 BCSC Basic and Clinical Science Course™
2 Fundamentals and Principles of Ophthalmology
Part III: Genetics
Chapter 6: Clinical Genetics
Genes and Chromosomes
Two allelic genes, which occupy the same gene locus on 2 homologous chromosomes, separate with the division of the 2 chromosomes during meiosis, and each goes to a different gamete. Thus, the genes are said to segregate, a property limited to allelic genes, which cannot occur together in a single offspring of the bearer. For example, if a parent is a compound heterozygote for both hemoglobin S and hemoglobin C, which occupy the same genetic locus on homologous chromosomes, then none of the offspring will inherit both hemoglobins from that parent; each will inherit either one or the other.
Figure 6-5 Normal meiosis and chromosomal nondisjunction (blue boxes) occurring at different phases of meiosis.
(Illustration by Cyndie C.H. Wooley.)
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.