Chromosomal Basis of Inheritance (1C) Practice Test

In a plant species, a recessive allele d causes dwarfism. A dwarf plant (d/d) is crossed with a heterozygous plant (D/d). Cytological analysis of the heterozygous parent reveals a reciprocal translocation between two nonhomologous chromosomes; the heterozygote is a translocation carrier but phenotypically normal. In the offspring, many seeds abort early, and among the surviving seedlings the ratio of normal:dwarf is close to 1:1. Which explanation best accounts for the observed seed abortion and the surviving phenotype ratio?

In a diploid frog species, a specific autosome carries a visible cytological inversion in one homolog (an inversion heterozygote). Researchers cross an inversion heterozygote to a normal homozygote and score offspring viability. They observe a substantial fraction of embryos that arrest early, while surviving offspring inherit either the normal arrangement or the inverted arrangement without obvious recombination within the inverted segment. Which explanation best accounts for reduced viability and suppressed recovery of recombinants within the inversion?