Mendel's Inheritance

All studies about the hypotheses of Mendel are called the Mendelian genetics.

Among the studies about peas of Mendel, the studies about the colour of seed coats, appearance of the seed coats and the height of stems were commonly adopted by school textbooks. In his studies, Mendel grew the plants, and carried out artificial pollination until the plants could constantly express a specific characteristic. Then, the plants would be used in his experiments. These plants were called "true-breeds".

In the experiments about the colour of seed coats of peas, Mendel grew the true-breed peas bearing yellow seed coats and green seed coats separately, and carried out artificial pollination within the same kind. After the harvast of the peas he grew these peas and carried out artificial pollination between the two types of plants. When he harvastsed the peas again, he found that about 3/4 of the seeds bearing yellow seed coats and the rest, about 1/4 bearing green seed coats. Thereafter, he repeated his experiments and extended to test on other properties. All gave similar results.

Eventually, Mendel concluded his studies and made up the Mendel's Law of inheritance.

The followings were included in Mendel's conclusion.

(1)	All hereditary traits were discrete units. They could exist together, but they would not interfere each other.
(2)	Each hereditary trait was controlled by two factors. The two factors of a trait of a certain individual could be the same or not the same. If both factors would present the same trait, then, this hereditary trait would be shown. If the two factors of a trait of an individual were different, then, only one could present its characteristic. The factor that is presented is said to be "dominant", otherwise, it is said to be "recessive". This is the dominance and recessiveness of the traits.
(3)	In the process of producing gametes, the two factors of each trait would be separated into different gametes. The separation of factors would not affect each other. This is the Law of segregation.
(4)	In the formation of zygote, gametes would combine. In the combination of gametes factors of a specific trait would come from different gametes and pair up. The pairing up of factors of each trait would not affect each other. This is known as the Law of independent assortment.

If the colour of seed coats of peas is taken as example, the following points would be obtained according to the above hypotheses.

(1)	The colour of seed coat is a hereditary trait. It is an independent unit.
(2)	In the control of seed coats, the trait is controlled by two factors. One makes the seed coat take the yellow colour, another makes it take the green colour.
(3)	In a specific individual, the two factors of this trait can be the same. As both factors make the seed coat take yellow colour, then, the seed coat would be yellow. Otherwise, the seed coat would be green. If the two factors are different and yellow colour is shown, then, yellow colour factor is the dominant character. If green colour cannot be shown, then, green colour factor is said to be recessive.
(4)	In the formation of gametes, the two factors would be separated into different gametes, and the separation of these two factors would not be affected by the separation of factors of other hereditary trait.
(5)	When the gametes combine to make a zygote, the two factors of the trait will come from different gametes. The assembling of the two factors of the trait will be not affected by the assembling of factors of other hereditary trait.

(09.09.2006)