Genetics study guide

Genetic variation refers to the presence of differences in the DNA sequences among individuals within a population of a species. This extensive variety is crucial for a population's ability to adapt to changing environmental conditions. These variations primarily arise through mutations, which are alterations in the genetic material (DNA). While many mutations are neutral or harmful, some can be beneficial, providing new traits that natural selection can act upon. The accumulation of these mutations over generations leads to the wide range of phenotypes observed within a species. Without this genetic diversity, populations would be far less resilient to challenges like disease or climate change, making it a cornerstone of evolutionary processes.

The inheritance of the ABO blood groups is a classic example of both multiple alleles and codominance. Unlike traits determined by two alleles, the ABO system involves three different alleles for a single gene: Iᔧ, Iᔥ, and i. The Iᔧ allele codes for the A antigen on red blood cells, while the Iᔥ allele codes for the B antigen. The allele i codes for no antigen. Alleles Iᔧ and Iᔥ are codominant with each other, meaning that if both are present in an individual (genotype IᔧIᔥ), both A and B antigens will be expressed, resulting in blood type AB. However, both Iᔧ and Iᔥ are dominant over the i allele. This means a person with genotype Iᔧi will have blood type A, and a person with genotype Iᔥi will have blood type B. Individuals with genotype ii will have blood type O. This genetic system explains the four primary blood types: A, B, AB, and O, and their specific inheritance patterns.