Question

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question 9

Answer 1

Mendel performed an 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 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.

Answer 2

Mendel followed the inheritance of 7 traits in pea plants (Pisum sativum). He chose traits that had 2 forms:

Pea shape (round or wrinkled)

Pea colour (yellow or green)

Flower colour (purple or white)

Flower position (terminal or axial)

Plant height (tall or short)

Pod shape (inflated or constricted)

Pod colour (yellow or green).

Mendel began with pure-breeding pea plants because they always produced progeny with the same characteristics as the parent plant. Mendel cross-bred these pea plants and recorded the traits of their progeny over several generations.

Mendel’s principles of inheritance

Key principles of genetics were developed from Mendel’s studies on peas.  

1. Fundamental theory of heredity

Inheritance involves the passing of discrete units of inheritance, or genes, from parents to offspring.

Mendel found that paired pea traits were either dominant or recessive. When pure-bred parent plants were cross-bred, dominant traits were always seen in the progeny, whereas recessive traits were hidden until the first-generation (F1) hybrid plants were left to self-pollinate. Mendel counted the number of second-generation (F2) progeny with dominant or recessive traits and found a 3:1 ratio of dominant to recessive traits. He concluded that traits were not blended but remained distinct in subsequent generations, which was contrary to scientific opinion at the time.

Mendel didn’t know about genes or discover genes, but he did speculate that there were 2 factors for each basic trait and that 1 factor was inherited from each parent.

We now know that Mendel’s inheritance factors are genes, or more specifically alleles – different variants of the same gene. In today’s genetic language, a pure-breeding pea plant line is a homozygote – it has 2 identical copies of the same allele. An F1 cross-bred pea plant is a heterozygote – it has 2 different alleles.