A plant species X with n=5 chromosomes was crossed with a related species Y with

Question

A plant species X with n=5 chromosomes was crossed with a related species Y with n = 7 chromosomes. The F1 hybrids produced only a few pollen grains, which were used to fertilize the ovules of related species Z with n=7 chromosomes. A few plants were produced from this cross, and all had 19 chromosomes. The F1 hybrids (with 19 chromosomes) were mated with related species W with n=11 chromosomes. A few plants were produced from the cross and all had 30 chromosomes. Following self-fertilization of the F1 hybrids a few F2 plants were produced, each with 60 chromosomes. These plants were phenotypically different from either of the original species and were highly fertile.

Explanation / Answer

The f1 hybrid had 5 chromosemes from specie x and 7 chromosome from specie 7.Total (5 + 7) = 12.

when back crossed specie Z. total = (12 + 7) = 19.This hybrid will be triploid.

Upon self fertilization ( 2x5=10) + (2x7=14) = 24.The F2 plants would therfore be alltetraploids.

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