Question

multiple choice 1 point
why does this karyotype show three copies of chromosome 18? (dok2)
nondisjunction caused an extra copy of chromosome 18, resulting in trisomy 18
the individual has a normal chromosome number but unusual chromosome shape
a deletion occurred removing one chromosome 18
the chromosomes failed to replicate before cell division

Explanation:

Nondisjunction during cell - division can cause an extra copy of a chromosome, leading to trisomy. In this case, nondisjunction likely led to an extra copy of chromosome 18. The other options are incorrect as they do not explain the presence of three copies. A normal chromosome number would mean two copies of chromosome 18, a deletion would reduce the number of chromosome 18 copies, and failure to replicate would result in fewer chromosomes.

Answer:

Nondisjunction caused an extra copy of chromosome 18, resulting in trisomy 18