Genetics Picture

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Different types of inheritence

Dominant - recessive

Gregor Johann Mendel, the father of genetics, experimented with pea plants. As we mentioned before, one of the things he looked at (that he studied) was the colour of the flowers. He started with two pea species which in cultivating had shown to be stable with regards to the colour of the flower. One strain gave always red flowers and the other strain only white flowers. Mendel crossed these strains by transferring pollen from one kind to the pistil of the other. The result was plants which had only red flowers. These plants then were allowed to reproduce by themselves. This time the offspring was not homogenous. About three quarters had red flowers and one quarter of the plants had white flowers. One calls this a splitting between two different types with a splitting ratio of 3:1, which shows the number plants with red flowers and those with white flowers (see below). Mendel assumed that all plants, which resulted from that crossing between the two types, contained the predispositions for both read and white. He assumed also that the red color had a stronger influence than the white. He hence called the stronger influential predisposition for dominant. The weaker capacity he called recessive. He declared that the dominant gene for red flowers completely hid the recessive gene for white flowers in the heterozygotic plants.

Dominance

There can be two different types of gametes present in each of the parents:
Gametes from the male - fr and fw
Gametes from the female - fr and fw

_______________________________________
|    |              |                 |
|    | fr           |  fw             |
|____|______________|_________________|
|    |              |                 |
| fr | frfr         |  frfw           |
|    | Red flower   |  Red flower     |
|____|______________|_________________|
|    |              |                 |
| fw | frfw         |  fwfw           |
|    | Red flower   |  White flower   |
|____|______________|_________________|

Splitting ratio 3 red : 1 white

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