Question

Individuals with Down syndrome have three copies of chromosome 21. The extra copy is most likely to be due to ______ during meiosis I on the oocyte.

1) Non-disjunction
2) Crossing over
3) Independent assortment
4) Mutation

Answer 1

Non-disjunction during meiosis I on the oocyte is responsible for the extra copy of chromosome 21 in individuals with Down syndrome.

Step-by-step explanation:

The extra copy of chromosome 21 in individuals with Down syndrome is most likely due to non-disjunction during meiosis I on the oocyte. Non-disjunction is the failure of chromosomes to separate properly during cell division, resulting in an incorrect distribution of chromosomes in the resulting gametes.