Mendel published his work on inheritance of characters in 1865 but for several reasons, it remained unrecognised till 1900. Firstly,
Which of the following statements are correct regarding true-breeding lines in the context of Mendelian genetics? S1. A true-breeding line consistently shows stable trait inheritance and expression for several generations upon continuous self-pollination. S2. They are produced by repeatedly crossing individuals with different desirable characters. S3. Mendel used true-breeding lines to ensure that the parental generation exhibited homozygous traits. S4. True-breeding lines are unsuitable for hybridisation experiments because they lack genetic variation. S5. If a true-breeding tall pea plant (TT) is self-pollinated, all its progeny will exhibit the dwarf phenotype.
Correct answer: A — S1 and S3 only
The core concept is the definition and significance of true-breeding lines in Mendelian genetics. S1. NCERT states: 'A true-breeding line is one that, having undergone continuous self-pollination, shows the stable trait inheritance and expression for several generations.' So, S1 is correct. S2. True-breeding lines are typically established through continuous self-pollination, not cross-pollination of different individuals. Repeated self-pollination leads to homozygosity. So, S2 is NOT correct. S3. By using true-breeding lines (e.g., TT for tall, tt for dwarf), Mendel ensured that the parental plants were homozygous for the traits being studied, providing a clear starting point for crosses. So, S3 is correct. S4. True-breeding lines are essential for hybridisation experiments as they provide known, stable parental genotypes. So, S4 is NOT correct. S5. If a true-breeding tall pea plant (genotype TT) is self-pollinated, all its progeny will also be tall (TT), not dwarf. So, S5 is NOT correct. Therefore, only statements S1 and S3 are correct. The tested concept is the definition, formation, and utility of true-breeding lines in genetic studies.
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