Lakhmir Singh Solutions Class 10 Biology Solutions for Exercise in Chapter 4 - Heredity and Evolution

Question 21 Exercise

(a) How do Mendel's experiments show that traits may be dominant or recessive?

(b) How do Mendel's experiments show that traits are inherited independently?


(a) Mendel conducted the experiments using or pea plant. He selected homozygous tall (TT) and dwarf (tt) pea plants. He crossed the tall pea plant with the dwarf pea plant. It was observed that the F1 generation are all tall plants. Thus, it was concluded that the gene causing tallness is dominant while the gene causing dwarfness is recessive. The trait expressing itself in the hybrid is the dominant one. This experiment proves Mendel’s first law of inheritance. It states that when a pair of contrasting factors is brought in a hybrid, one factor inhibits the appearance of the other, one which inhibits is the dominant one and which is inhibited is recessive.

(b) Mendel performed experiments in which he took a tall plant with round seeds and a short plant with wrinkled-seeds. In F1, They were all tall and had round seeds. Tallness and round seeds were thus dominant traits. When he used these F1 progeny to generate F2 progeny by self-pollination, he found that some F2 progeny were tall plants with round seeds, and some were short plants with wrinkled seeds. At the same time, there were tall plants, but had wrinkled seeds, while others were short, but had round seeds. Thus, Mendel’s experiments show that the tall/short trait and the round seed/wrinkled seed trait are independently inherited.

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