Show me an example!!William Bateson experimented with chickens. He found that there were red chickens and white chickens. If he bred the red chickens the offspring were always red. If he bred the white chickens, the offspring were always white:
In the pictures, the two 'alleles' of the colour gene are down as red or white rectangles next to each chicken.
If he bred the red chickens with the white chickens, the offspring were always red.
Each child would get one of the two red alleles (at random) from the mummy and one of the two white alleles (at random) from the daddy. In any of the 4 possible combinations, the children would always have one red and one white allele.
The red allele of the colour gene is dominant, so all the children are red, even though they have one red allele and one white allele.
Now, if he bred the offspring with one another, on average, one in four of the offspring were white and three in four were red.
Each child would get either a red allele or a white allele (at random) from the mummy and would get either a red allele or a white allele (at random) from the daddy.
There are two ways in which a child can get a mixture of red and white alleles and one way in which it can get both red or both white. Since the red genes are dominant, three of the children are red and one is white.
Remember this is an on average effect, since it is completely random which version of the gene is inherited by one of the children.