Biology / Unit 6 Bio 1187 short lesson, about 20 seconds
Nondisjunction
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The idea
Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during meiosis, leaving gametes with an abnormal chromosome number.
In practice
A homolog pair that fails to separate at anaphase I sends both copies into one gamete and none into the other.
Where people slip
Nondisjunction can occur in meiosis I or meiosis II, and the two failures produce different mixes of abnormal gametes.
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