What is dihybrid cross? explain with suitable example and checker board method
Answers
Explanation:
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.
The Dihybrid cross is easy to visualize using a Punnett square of dimensions 16:
RY Ry rY ry
RY RRYY RRYy RrYY RrYy
Ry RRYy RRyy RrYy Rryy
rY RrYY RrYy. rrYY rrYy
ry RrYy Rryy rrYy rryy
The rules of meiosis, as they apply to the dihybrid, are codified in Mendel's first law and Mendel's second law, which are also called the Law of Segregation and the Law of Independent Assortment, respectively.
For genes on separate chromosomes, each allele pair showed independent segregation. 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 GENOTYPIC RATIO=1:2:1:2:4:2:1:2:1