Question

Which of Mendel’s laws are you exploiting in the analysis of a dihybrid cross? Explain.

Answer 1

Mendle's second law , the law of independent assortment is exploited in the dihybrid cross.

This law states that the alleles of two different genes get sorted into gametes independently of one another.

The dominance relationship between alleles for each trait was already know to mendel when he made the cross. The purpose behind the dihybrid cross was to determine if any relationship existed between different allelic pairs , and the results from this dihybrid cross helped mendel to formulate his second law , the law of independent assortment. During, the gamete formation the segregation of alleles of one allelic pair is independent of the alleles of another allelic pair.

Independent assortment takes place during the process of meiosis. In this the chromosomes are halved and are known as haploid.

In the dihybrid cross , mendel choosed round yellow seed and wrinkled green seed and crossed them. He obtained only round yellow seeds in the F1 generation, and later on self pollination of F1 progeny gave four different combinations of seeds in the F2 generation. He obtained round yellow , wrinkled yellow, round green and wrinkled green seeds in the phenotypic ratio 9:3:3:1.

Hence the cross between the parental genotype round yellow seeds(RRYY) and green wrinkled seeds(rryy) explains this.Here the chances of formation of gametes with the gene R and the gene r are 50:50. Also the formation of gametes with the gene Y and the gene y is 50:50. Thus, each gamete should have either R or r and Y or y.

The law of independent assortment states that the segregation of Rand r is independent of the segregation of Y and y. This results in four types of gametes RY, Ry, rY and ry. These combinations of alleles are different from their parental combinations (RR,YY,rr,yy).

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