Genetics study guide

Asexual reproduction involves a single parent producing offspring that are genetically identical to itself. One significant benefit is that individuals do not need to find a mate, which can save energy and time, particularly in sparse populations or challenging environments. This allows for rapid colonisation of new areas, as a single organism can quickly multiply without the need for another. The reproductive cycle can be very fast, leading to a rapid increase in population size. However, a major limitation is the lack of genetic variation within the population. Since offspring are clones, they all share the same genetic make-up. This can be detrimental if environmental conditions change, such as the introduction of a new disease or a shift in climate. If one individual is susceptible to a particular threat, all individuals in the population are likely to be equally susceptible, potentially leading to the extinction of the entire population. In contrast, sexual reproduction introduces genetic variation, increasing the chances that some individuals will survive environmental changes due to advantageous traits.

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.