Nondisjunction and chromosomal disorders Original Scenario-Based Download PDF

Questions

1. 1.

   In an arboreal sanctuary on an orbital station, biologists cultivate the luminescent crystal-frog (Cryophryne vitrea), a diploid organism with $2n = 24$ chromosomes. During spermatogenesis in one lineage, a single pair of homologous chromosomes fails to segregate during anaphase I, while all other chromosomes divide typically. Both daughter cells subsequently undergo anaphase II without any segregation errors, and one of the resulting sperm successfully fertilizes a typical haploid ovum from a wild-type female. Which prediction correctly identifies the chromosome constitution of the gametes produced by this meiotic event and the ploidy condition of the resulting zygote?

   • A) Exactly half of the gametes carry the normal chromosome count of 12, while the other half are divided between 11 and 13, producing a monosomic zygote with 23 chromosomes.
   • B) The segregation failure doubles the entire chromosome complement across all gametes, resulting in diploid sperm that yield a viable triploid zygote with 36 chromosomes.
   • C) All four gametes will be genetically identical and carry 13 chromosomes each, leading without exception to a tetrasomic zygote with 26 chromosomes.
   • D) All four gametes are aneuploid, with half containing 13 chromosomes and half containing 11, such that fertilization of a 13-chromosome sperm produces a trisomic zygote with 25 chromosomes.