CBSE Class 10 Science 2022 · Paper 31(B)/5 · Question 5
Pea plants were grown in two fields, X and Y. While field X produced pea plants with white flowers, field Y produced pea plants with blue flowers. In subsequent generations, it was observed that in the field X, the offsprings exhibited only the parental characters whereas in the field Y, majority of the offsprings exhibited variation in characters. State the possible reasons for these observations.
Answer
Field X plants were pure-breeding and self-pollinated, giving no new gene combinations; field Y plants were cross-pollinated, giving new combinations and variation.
Field X: The white-flowered plants were most likely pure-breeding (true-breeding) and reproduced by self-pollination, the pollen and the egg coming from the same plant (the garden pea flower normally pollinates itself). So the offspring received the same set of genes as their parents, no new combinations of genes were formed, and they showed only the parental characters. (In Mendel's peas white is recessive, so white-flowered plants carry only the gene for white and breed true.)
Field Y: The blue-flowered plants were most likely cross-pollinated, receiving pollen from other, genetically different plants, or were themselves hybrids. Sexual reproduction between different parents combines their DNA, so the offspring received new combinations of genes, and most of them showed variation in their characters.
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