A plant species X with n=5 was crossed with a related species Y with n=7. The F1 hybrids produced only a few pollen grains, which were used to fertilize the ovules of species Y. A few plants were produced from this cross, and all had 19 chromosomes. Following a self-fertilization, the F1 hybrids produced a few F2 plants, each with 24 chromosomes. These plants were phenotypically different from either of the original species and were highly fertile. Explain by diagram and description the events that produced these fertile F2 hybrids.
Possible scenario.
Plant X (n=5) cross Plant Y (n=7).
You get hybrid 2n=12 (from 5+7).
This hybrid produced 2n gamete (paternal side = pollen grain) due to non-disjunction (n=12).
Cross with ovules from Plant Y (n=7), and you get F1 (3n=19).
To get F2 plant with 24 gametes, F1 plant must produce gametes exclusively from the paternal side (n=12) and these fused to form zygote which will develop into fertile F2 hybrid.
Sham
