Till now we have discussed about the Mendel’s hypothesis with monohybrid cross. Mendel’s also tried to understand the inheritance of two pairs of characters together. In this dihybrid cross, parents produce offsprings containing the factors for Characters (traits) of Yellow (YY), Round (RR), and wrinkled (rr), green (yy).

These characters appeared independently without mixing with each other in F2 generation, which were produced by self pollination in F1 generation.

Observe thc checker board given here carefully and note down different combinations of characters resulted from dihybrid cross.

1. RRYY, 2. RRYy, 3. RrYY, 4. RrYy, 5. RRYy, 6. RrYY, 7. RrYy, 8. RrYy, 9. RrYy are having Round Round yellow Wrinkled, yellow Round, green Wrinkled, green and Yellow seeds. 1. RRyy, 2. Rryy, 3. Rryy have Round and Green seeds

1. rrYY, 2. rrYy, 3. rrYy have Wrinkled and Yellow seeds 1. rryy have Wrinkled and Green seeds From the above results it can be concluded that the factors for each character or trait remain independent and maintain their identity in the gametes.

The factors are independent to each other and passes to the offsprings (through gametes). In the inheritance of more than one pair of characters (traits), the factors for each pair of characters assorted independently of the other pair. This is known as “Law of independent assortment”.

Mendel believed that every character or trait is controlled or responsible by a pair of factors. The factors which are responsible for a character or trait of an organism, now named as ‘genes’.

The pair of genes which are responsible for a character are called as ‘alleles’. Alleles are of two types one is homozygous type (YY or RR) and the other is heterozygous (Yy or Rr).