What condition is described by non-disjunction?

Non-disjunction is a genetic condition that occurs when chromosomes or chromatids fail to separate properly during cell division, particularly during meiosis or mitosis. This failure can lead to an abnormal distribution of chromosomes in the resulting daughter cells.

When we consider the options, the gain of a chromosome refers to an individual having an extra chromosome, such as in trisomy, where three copies of a chromosome are present instead of the usual two. This can result from non-disjunction during meiosis, leading to gametes that possess an additional chromosome.

Conversely, the loss of a chromosome is also a possible outcome of non-disjunction, where one of the resulting gametes ends up lacking a chromosome altogether, leading to conditions like monosomy, where only one chromosome of a particular type is present in the pair.

The essential aspect of non-disjunction is the failure of chromatids to separate during the process of meiosis, leading to these gains or losses of chromosomes. This failure can have significant implications for the genetic composition of the next generation, leading to various genetic disorders.

Therefore, the option that encompasses all of these aspects—gain of a chromosome, loss of a chromosome, and the fundamental issue of chromatids failing to separate—is most accurately represented by the