What can result from nondisjunction during meiosis?

Nondisjunction during meiosis refers to the failure of homologous chromosomes or sister chromatids to separate properly during cell division. This error can lead to gametes that contain an abnormal number of chromosomes, resulting in either aneuploidy—where gametes have an extra chromosome (trisomy) or a missing chromosome (monosomy). When these abnormal gametes participate in fertilization, they can lead to conditions such as Down syndrome (trisomy 21), Turner syndrome (monosomy X), and several other chromosome-related disorders.

The other options either describe outcomes that do not occur as a result of nondisjunction or suggest scenarios that do not relate to the implications of abnormal chromosome numbers. For instance, normal development of all gametes does not happen when nondisjunction occurs, and genetic variability as a result of crossover events in meiosis is not directly linked to nondisjunction. Likewise, non-disjunction does not indicate better reproductive success, as it often leads to genetic disorders and decreased viability of the resulting zygotes. Therefore, the phenomenon of nondisjunction clearly results in gametes that contain either too many or too few chromosomes, which confirms that the correct answer pertains to this consequence.