Question

what is dihybrid cross and example and the ratio of this cross​

Answer 1

In the name "Dihybrid cross", the "di" indicates that there are two traits involved (e.g. R and Y), the "hybrid" means that each trait has two different alleles (e.g. R and r, or Y and y), and "cross" means that there are two individuals (usually a mother and father) who are combining or "crossing" their genetic information.

If the first filial generation (F1 generation) produces four identical offspring, the second filial generation, which occurs by crossing the members of the first filial generation, shows a phenotypic (appearance) ratio of 9:3:3:1, where:

The 9 represents the proportion of individuals displaying both dominant traits:

RRYY + 2 x RRYy + 2 x RrYY + 4 x RrYy

the first 3 represents the individuals displaying the first dominant trait and the second recessive trait:

RRyy + 2 x Rryy

the second 3 represents those displaying the first recessive trait and second dominant trait:

rrYY + 2 x rrYy

the 1 represents the homozygous, displaying both recessive traits:

rryy

The Dihybrid ratio=9:3:3:1

Answer 2

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In this Dihybrid Cross, homozygous dominant traits were crossed with homozygous recessive traits. This particular cross always results in the phenotypic ratio of 1:0:0:0 meaning that the offspring will all have both dominant phenotypes but will be carriers of the recessive phenotypes.