Question

Which mutation causes either the inclusion of an extra chromosome in offspring or the deletion of an entire chromosome?
A) deletion
B) insertion
C) crossing-over
D) non-disjunction

Answer 1

Answer: D)non-disjunction

Explanation:

Our cells have 46 chromosomes (23 pairs). When a cell divides (mitosis or meiosis) and there is no separation of homologous chromosomes (equal to each other or forming a pair) a disjunction creates a cell or gamete (eggs and sperm) with more or less genetic material. A classic example of non-disjunction is the selection of chromosomes 21 in meiosis, producing fertilized gametes resulting in Down Syndrome or free chromosome 21 trisomy.