Question

A non disjunction event affecting chromosome 13 occurred during the first meiotic division in a woman. Following fertilization, how many chromosomes would you expect to find in the somatic cells of the resulting embryo?

a) 45 or 47
b) 47
c) 45, 46, 47
d) 45

Answer 1

The embryo would have either 45 or 47 chromosomes in the somatic cells as a result of nondisjunction in meiosis I, leading to trisomy or monosomy for chromosome 13.

Step-by-step explanation:

If a nondisjunction event affecting chromosome 13 occurs during the first meiotic division in a woman, the resulting embryo's somatic cells would either have one extra chromosome (47 chromosomes) or one less chromosome (45 chromosomes), but not the normal number (46 chromosomes). This is because during nondisjunction in meiosis I, the homologous chromosomes do not separate properly. As a result, two gametes will have an additional chromosome (n + 1) and two will have one fewer chromosome (n - 1). If a normal sperm fertilizes an egg with this abnormality, the embryo will either have trisomy (an extra chromosome) or monosomy (a missing chromosome). The correct answer to the proposed question is: a) 45 or 47 chromosomes.