What does nullisomy refer to in genetic terms?

Nullisomy refers to the loss of both members of a homologous chromosome pair in an organism's genome. This condition results in the absence of a particular chromosome, leading to a 2n-2 chromosome complement in diploid organisms, where "n" represents the normal number of chromosomes. The key aspect of nullisomy is that it encompasses the complete loss of both chromosomes from a pair, which can have significant implications for cellular function and development, as the organism lacks the genetic material that those chromosomes would typically provide.

In contrast, gains or losses of single chromosomes or the presence of extra chromosomes would not be classified as nullisomy. For instance, an extra chromosome would indicate a non-disjunction event leading to trisomy, while losing only one member of a homologous pair would refer to monosomy. Understanding these distinctions is critical for grasping concepts related to chromosomal abnormalities and their effects on phenotypes.