Question

explain the experiment carried out by the Mendel to the study of Inheritance of one gene

Answer 1

Mendel carried out breeding experiments in his monastery’s garden to test inheritance patterns. He selectively cross-bred common pea plants (Pisum sativum) with selected traits over several generations. After crossing two plants which differed in a single trait (tall stems vs. short stems, round peas vs. wrinkled peas, purple flowers vs. white flowers, etc), Mendel discovered that the next generation, the “F1” (first filial generation), was comprised entirely of individuals exhibiting only one of the traits. However, when this generation was interbred, its offspring, the “F2” (second filial generation), showed a 3:1 ratio- three individuals had the same trait as one parent and one individual had the other parent’s trait.

Mendel then theorized that genes can be made up of three possible pairings of heredity units, which he called ‘factors’: AA, Aa, and aa. The big ‘A’ represents the dominant factor and the little ‘a’ represents the recessive factor. In Mendel’s crosses, the starting plants were homozygous AA or aa, the F1 generation were Aa, and the F2 generation were AA, Aa, or aa. The interaction between these two determines the physical trait that is visible to us.

Mendel’s Law of Dominance predicts this interaction; it states that when mating occurs between two organisms of different traits, each offspring exhibits the trait of one parent only. If the dominant factor is present in an individual, the dominant trait will result. The recessive trait will only result if both factors are recessive.

Answer 2

Gregor Mendel developed the model of heredity that now bears his name by experiments on various charactersitics of pea plants: height (tall vs. Short); seed color (yellow vs. Green); seat coat (smooth vs. wrinkled), etc. The following explanation uses the tall/short trait. The other traits Mendel studied can be substituted for tall and short.

Mendel started out with plants that "bred true". That is, when tall plants were self-pollinated (or cross-pollinated with others like them), plants in following generations were all tall; when the short plants were self-pollinated (or cross- pollinated with others like them) the plants in following generations were all short. Mendel found that if true breeding Tall [T] plants are crossed (bred) with true breeding short [t] plants, all the next generation of plants, called F1, are all tall. Next, he showed that self-pollinated F1 plants (or cross- pollinated with other F1 plants) produce an F2 generation with 3/4 of the plants tall and 1/4 short. A. 1/4 of the F2 generation are short plants, which produce only short plants in the F3 generation, if they are self- pollinated (or crossed with other short F2 plants;) these F2 plants breed true. B, 1/4 of the F2 generation (1/3 of the tall plants) are tall plants that produce only tall plants in the F3 generation, if they are self-pollinated; these tall F2 plants breed true. C. 1/2 of the F2 generation (2/3 of the tall plants) are tall plants that produce 1/4 short plants and 3/4 tall plants in the next [F3] generation, if they are self-pollinated. This is the same proportion of tall to short that F1 plants produce.