Nondisjunction and chromosomal disorders Transitional Reasoning Download PDF

Questions

1. 1.

   In an animal species with a diploid chromosome number of $2n = 16$, a single homologous chromosome pair fails to separate during anaphase I of meiosis, while sister chromatids separate normally during anaphase II in all resulting secondary spermatocytes. What is the expected chromosomal composition of the four gametes produced at the end of this division, and what type of aneuploid zygote could form upon fertilization with a normal gamete ($n = 8$)?

   • A) Two gametes with $n = 8$, one with $n = 9$, and one with $n = 7$; yielding either a normal diploid or an aneuploid zygote.
   • B) Four gametes with $n = 9$; yielding only trisomic zygotes with $2n + 2 = 18$ chromosomes.
   • C) Two gametes with $n = 9$ and two gametes with $n = 7$; yielding either a trisomic zygote ($2n + 1 = 17$) or a monosomic zygote ($2n - 1 = 15$).
   • D) Four gametes with $n = 8$; yielding entirely normal diploid zygotes due to compensatory division during meiosis II.