Final answer:
Nullisomy is the form of aneuploidy where two members of the same homologous pair are absent, caused by nondisjunction during meiosis.
Step-by-step explanation:
The form of aneuploidy in which two members of the same homologous pair are absent is called nullisomy. This condition occurs due to nondisjunction, which is the failure of homologous chromosomes or sister chromatids to separate properly during meiosis.
Aneuploidy includes various chromosome number abnormalities such as monosomy (the loss of a single chromosome) and trisomy (the gain of an additional chromosome). In the case of nullisomy, an individual lacks both copies of a particular chromosome due to a failure in chromosome segregation.