Dihybrid Cross and Inheritance of Two Genes

The mystery of genetics was solved with the investigations of Gregor Johann Mendel. He was the first person who discovered the basic principles of heredity during the mid-nineteenth century. Hence he is known as the father of modern genetics. He conducted experiments in his garden on pea plants and observed their pattern of inheritance from one generation to next generation.

Let’s learn more about Mendel’s experiment – dihybrid cross and inheritance of two genes.

Mendel’s Experiment

Mendel is known as the father of genetics and he proposed the laws of inheritance: Law of Segregation, Law of Independent Assortment and  Law of Dominance. These laws came into existence from his experiments on pea plants with a variety of traits.

Mendel first studied the inheritance of one gene in the plant through monohybrid cross. He considered only a single character (plant height) on pairs of pea plants with one contrasting trait. Later, he studied the inheritance of two genes in the plant through dihybrid cross.

Mendel studied the following seven characters with contrasting traits:

  • Stem height: Tall/dwarf
  • Seed shape: Round/wrinkled
  • Seed color: Yellow/green
  • Pod color: Green/yellow
  • Pod shape: Inflated/constricted
  • Flower color: Violet/white
  • Flower position: Axial/terminal

Dihybrid Cross

In a dihybrid cross, Mendel took a pair of contradicting traits together for crossing; for example color and the shape of seeds at a time. He picked the wrinkled-green seed and round-yellow seed and crossed them. He obtained only round-yellow seeds in the F1 generation. This indicated that round shape and yellow color of seeds are dominant in nature. While the wrinkled shape and green color of seeds are recessive traits. Then, F1 progeny was self-pollinated. This resulted in four different combinations of seeds in F2 generation. They were wrinkled-yellow, round-yellow, wrinkled-green seeds and round-green in the phenotypic ratio of 9:3:3:1.

During monohybrid crosses of these traits, he observed the same pattern of dominance and inheritance. The phenotypic ratio 3:1 of yellow and green color and of round and wrinkled seed shape during monohybrid cross was retained in dihybrid cross as well.

Consider Y for yellow seed color and y for green seed color, R for round shaped seeds and r for wrinkled seed shape. Thus, the parental genotype will be RRYY (round-yellow seeds) and rryy (green-wrinkled seeds).

The dihybrid cross of both will give F1 progeny RrYy (round-yellow seeds) as shown in the figure.

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Practise This Question

A dihybrid tall plant with yellow flowers (TtYy) was crossed with a dwarf plant bearing white flowers (ttyy). What percentage of progeny is expected to be homozygous tall bearing yellow flowers?