[Biology Class Notes] on Dihybrid Cross Pdf

Dihybrid cross is the cross between two different genes that differ in two observed traits.

 

Gregor Johann Mendel was the first person who discovered the basic principles of heredity during the mid-19th century. Hence, he is known as the “Father of Modern Genetics”. He observed a pattern of inheritance from one generation to another by conducting experiments on the pea plants in his garden. 

 

Mendel’s Laws

Mendel laid the basic groundwork in the field of genetics and eventually proposed the laws of inheritance.

 

Law of Segregation, Law of Independent Assortment and Law of Dominance are the three laws of inheritance proposed by Gregor Mendel. These laws came into existence from his experiments on pea plants with a variety of traits.

 

Mendel’s Experiment Inference

By monohybrid cross only, Mendel could first study the inheritance of one gene in the plant. He considered only one character (plant height) on pairs of pea plants with one contrasting trait. Later also, through the same process of dihybrid cross, Mendel studies the inheritance of two genes in plants. 

Mendel studied the subsequent seven characters with contrasting traits:

• Stem Height: Tall/dwarf

• Seed Shape: Round/wrinkled

• Seed Colour: Yellow/green

• Pod Colour: Green/yellow

• Pod Shape: Inflated/constricted

• Flower Colour: Violet/white

• Flower Position: Axial/terminal

 

Dihybrid Cross 

A hybridization is a breeding experiment between two organisms which are identical hybrids for 2 traits. In other words, a dihybrid cross is a cross between two organisms, with both being heterozygous for two different traits. The individuals in this type of trait are homozygous for a specific trait. These traits are determined by DNA segments called genes.

 

In a hybridization, the parents carry different pairs of alleles for every trait. One parent carries homozygous dominant allele, while the other one carries homozygous recessive allele. The offspring produced after the crosses in the F1 generation are all heterozygous for specific traits.

 

Dihybrid Cross Examples

Mendel took a pair of contradicting traits together for crossing, for example colour and the shape of seeds at a time. He chose the green wrinkled seed and round-yellow seed and crossed them. He obtained only round-yellow seeds in the F1 generation. This indicated that the round shape and yellow colour of seeds are dominant in nature.

 

Meanwhile, the wrinkled shape and green colour of seeds are different traits. Then, F1 progeny was self-pollinated. This resulted in four different combinations of seeds in the F2 generation. They were wrinkled-yellow, round-yellow, wrinkled-green seeds and round-green within the phenotypic ratio of 9:3:3:1.

 

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

 

For example, consider“Y” for yellow colour seed and “y” for green color seed, “R” for round shaped seeds and “r” for wrinkled seed shape. Thus, the parental genotype can be concluded as “YYRR” (yellow-round seeds) and “yyrr” (green-wrinkled seeds).

 

Dihybrid Cross Is Easy To Understand Using Punnett Square Dimensions of 16: 

Things to Remember:

• Dihybrid crossing is the crossing between the genes to genes that vary in two practical traits.

• Mendel was the first person to discover the fundamental principles of heredity. After that, he is known as the “Father of Modern Genetics”.

• Mendel suggests the three laws of inheritance. These laws are independent assortment law, segregation law, and the law of dominance. 

• Mendel observes a law of inheritance from two generations by experimenting with pea plants.