Two Alleles Inheritance

The inheritance of shapes of seeds and colours of seed coats of peas

According to the hypotheses of Mendel, the shapes of peas and colours of seed coats of peas are different traits. They should be controlled by different and not interfering genetic factors.

Let	Y be the dominant allele showing yellow seed coat in the trait of colour of seed coats; then
	y be the recessive allele showing green colour in seed coats.
	R be the dominant allele giving round seeds in the trait of the shape of seed coats; then,
	r be the recessive allele giving wrinkled seeds in the trait.

Therefore,	the genotype of the round pea with yellow seed coat must be : YYRR;
	the genotype of the wrinkled pea with green seed coat must be : yyrr

The parent are the pea plants with round pea and yellow seed coat and that with wrinkled pea and green seed coat.

The pea with round seed and yellow seed coat can produce one type of gamete only. Its genotype is : YR
The genotype of the pea with wrinkled pea and green seed coat is : yr

The fertilization of their gametes give rise to a new generation, F₁. Then, there is only one genotype for their descendents. It is : YyRrĄC
So, all members of F₁ should have the phenotype of round seed and yellow seed coat.

As there is only one genotype in F₁, that is YyRr , each of them can produce 4 types of gametes : YR, Yr, yR and yr. Their descendents would be as follow.

Individual 1		YyRr
Individual 2	Gamete	YR	Yr	yR	yr
YyRr	YR	YYRR	YYRr	YyRR	YyRr
	Yr	YYRr	YYrr	YyRr	Yyrr
	yR	YyRR	YyRr	yyRR	yyRr
	yr	YyRr	Yyrr	yyRr	yyrr

So, the statistics of the F₂ members should be as follow.

(1)	The genotypic ration is YYRR : YYRr : YYrr : YyRR : YyRr : Yyrr : yyRR : yyRr : yyrr = 1:2:1:2:4:2:1:2:1
(2)	The phenotypic frequency is : Round and yellow seed coat ĄG Wrinkled and yellow seed coat ĄG Round and green seed coat ĄG Wrinkled and green seed coat = 9 : 3 : 3 : 1

(16.09.2006)