Describe inheritance of two gene.

Explanation

Mendel also worked with and crossed pea plants that differed in two characters as is seen in the cross between a pea plant that has seeds with yellow colour and round shape and one that had seeds of green colour and wrinkled shape.
= Mendel found that the seeds resulting from the crossing of the parents had yellow coloured and round shaped seeds.
= Thus yellow colour was dominant over green and round shape dominant over wrinkled.
= These results were identical to those that he got when he made separate monohybrid crosses between yellow and green seeded plants and between round and wrinkled seeded plants.
= Let us use the genotypic symbols .Y. for dominant yellow seed colour and .y. for recessive green seed colour, R for round shaped seeds and r for wrinkled seed shape.
= The genotype of the parents can then be written as RRYY and rryy.
= The cross between the two plants can be written down as in the given figure showing the genotypes of the parent plants.
= The gametes RY and ry unite on fertilisation to produce the `F_1`, hybrid RrYy.
= When Mendel self hybridised the `F_1` plants he found that `3//4^(th)` of `F_2` plants had yellow seeds and 1/`4^(th)` had green.
= The yellow and green colour segregated in a 3:1 ratio.
= Round and wrinkled seed shape also segregated in a 3:1 ratio, just like in a monohybrid cross.