Dihybrid Cross of Mendel and Inheritance of Two Genes: Introduction, Examples, FAQ

What Is Dihybrid Cross?

A dihybrid cross is a cross-breeding carried out for two different characters at a time to study their blended inheritance pattern. In this cross, organisms with contrasting characters in two traits are being crossed to have the segregation and assortment mechanism of such traits analyzed concerning this law. This setup is very important in genetics as it enables the researcher to observe the transmission of many characters and how genes on the different chromosomes behave during gamete formation. The heredity concept was initiated in the mid 19 century by the Austrian monk Gregor Mendel commonly referred to as the father of genetics. His findings regarding basic genetics, segregation, and independent assessment threw light on the science of biology owing to his prowess in solving problems related to heredity.

Mendel's Experiment On Dihybrid Cross

Mendel’s experiments on dihybrid cross is explained below-

Objective Of The Experiment

The general significance of Mendel’s work is evidenced by the current application of genetics in various areas ranging from the breeding of crops for increased yield and disease resistance to that of gene therapy in medical sciences; it indicates how his work laid down the basis upon which people are gradually building their understanding of the principles of biological heredity.

Methodology

The specific purpose of Mendel’s dihybrid cross-experiment was to study the characteristics of two different factors together in one organism at a time specifically in pea plants or Pisum sativum. In doing so, he hoped that he could disprove or prove his hypothesis of the Law of Independent Assortment by analyzing the way Genetic Traits such as Seed Shape and Seed Color are inherited.

The garden pea was thus chosen by Mendel for experiments because it has very distinguishable characteristics. Specifically, he chose plants that exhibited two traits: such factors as seed size (round or wrinkled), and seed pigmentation (yellow or green). Before performing his dihybrid cross, Mendel had to make the parental plants pure, which he achieved by letting the plants self-breed for generations, thus making sure that the parents were homozygous for both the traits – round yellow seeds (RRYY) and wrinkled green seeds (rryy).

The Dihybrid Cross

Dihybrid cross is explained below-

First Filial Generation (F1)

In Mendel's dihybrid cross experiment, the first filial generation (F1) resulted from crossing pea plants with different traits: Round yellow seeds (RRYY) and wrinkled green seeds (rryy) as the round yellow seeds are dominant over the wrinkled green seeds. The F1 generation as expected was phenotypically uniform, with all the plants having round yellow seeds. This outcome indicated that one phenotype possessed superior characteristics of being round and yellow over the other phenotype that was wrinkled and green in colour.

Phenotypic Ratio: Fully round with a bright yellow outer coat with no hilum basin and smooth surface.

Genotypic Ratio: Let all the plants be RrYy type for simply the two characteristic features are rolling and yellow seed.

Second Filial Generation (F2)

Crossing over the F1 generation plants gave Mendel the second filial generation or the F2 generation. The F2 generation exhibited a phenotypic ratio of 9:3:3:1 which means sixteen young ones:

Nine of them possessed round yellow seeds which are represented by RRYY and RrYy.

3 belonged to round green seeds (RRyy and Rryy).

3 had wrinkled yellow seeds (both rrYY and rrYy genotypes).

1 had wrinkled green seeds (rryy).

Explanation Of Results Through Punnett Square

The 9:3:3:1 phenotypic ratio is easily explained by observing the allele relationships with the help of a Punnett square that demonstrates all the possibilities in the F1 generation. Every cell in a Punnett square is an individual genotype, while phenotypes come from the blend of the mentioned genotypes. This ratio can be said to conform with Mendel’s Law of independent assortment showing that alleles for seed shape round or wrinkle, are independent of alleles for seed colour yellow or green during gamete formation.

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