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What is dihybrid cross? Explain it with example.
The term "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.
A dihybrid cross describes a breeding experiment between two organisms that are identically hybrid for two traits (characteristics that are determined by segments of DNA called genes). A hybrid organism is one that is heterozygous, means that carries two different alleles at a particular genetic position.
Dihybrid Cross Example
For dihybrid cross also Mendel selected many pairs of contrasting characters. Let us take the example of seed colour and seed texture.
In this example, yellow (Y) and round (R) are dominant alleles and green (y) and wrinkled (r) are recessive.
Mendel took Round green seeds (RRyy) and wrinkled yellow seeds (rrYY) together for crossing. In this case, he obtained that all plants produced only round-yellow seeds with genotype 'RrYy' in the F1 generation. This indicated that round shape and yellow colour of seeds are dominant in nature, while the wrinkled shape and green colour of seeds are recessive traits. Then, plants of the F1 generation were allowed to self-pollinate, that results in F2 generation which revealed an interesting pattern.
The F2 generation exhibits 16 plants (produces total 556 seeds) with combinations of four different phenotype.
(i) 9 plants are with 315 round-yellow seeds RRYY,
(ii) 3 plants are with 101 wrinkled-yellow seeds rrYY,
(iii) 3 plants are with 108 round-green seeds RRyy and
(iv) 1 plant is with 32 wrinkled-green seeds rryy.
The phenotypic ratio of round yellow (RRYY), round green (RRyy), wrinkled yellow (rrYY) and wrinkled green (rryy) was 9:3:3:1.
This ratio can be estimated using a Punnett square to reveal possible consequences of the genetic cross.
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