Difference Between Monohybrid and Dihybrid Inheritance

The main difference between monohybrid and dihybrid inheritance is that the monohybrid inheritance describes the inheritance of a single pair of alleles whereas the dihybrid inheritance describes the inheritance of two pairs of independent alleles. Furthermore, the phenotypic ratio of F2 generation in monohybrid inheritance is 3:1 while the phenotypic ratio of F2 generation in dihybrid inheritance is 9:3:3:1.

Monohybrid and dihybrid inheritance are two types of inheritance patterns that obey the Mendelian inheritance.

Key Areas Covered

1. What is Monohybrid Inheritance
     – Definition, Cross Results, Mendel’s First Law
2. What is Dihybrid Inheritance
     – Definition, Cross Results, Mendel’s Second Law
3. What are the Similarities Between Monohybrid and Dihybrid Inheritance
     – Outline of Common Features
4. What is the Difference Between Monohybrid and Dihybrid Inheritance
     – Comparison of Key Differences

Key Terms

Dihybrid Inheritance, F2 Generation, Mendel’s First Law, Mendel’s Second Law, Monohybrid Inheritance

Difference Between Monohybrid and Dihybrid Inheritance – Side by Side Comparison

What is Monohybrid Inheritance

Monohybrid inheritance describes the inheritance patterns of a single trait. It occurs during monohybrid crossing. The parent used for the monohybrid cross comprises a pair of contrasting characters. Each parent is homozygous for the expressing character. When the two characters are crossed, the first or the F1 generation exhibits one of the two characters in the trait, which can be then identified as the dominant character. The unexpressed character is called the recessive character. When the two individuals of the F1 generation is crossed, the phenotypic ratio of the F2 generation can be observed as 3:1.

Figure 1: Monohybrid Cross

This idea is known as the principle of dominance and it is described by Mendel’s first law or the law of segregation. It describes the separation of the two factors or the alleles of a particular trait during the formation of gametes.

What is Dihybrid Inheritance

Dihybrid inheritance describes the inheritance patterns of two pairs of characters during a dihybrid cross. Pure breeding parents are used in a dihybrid cross. When the two pairs of characters are crossed, the F1 generation exhibits only two dominant characters. In the F2 generation, the phenotypic ratio is 9:3:3:1.

Figure 2: Dihybrid Cross

Mendel proposed his second law based on the results of the dihybrid cross, which is also known as the law of independent assortment. It means, although F1 generation exhibits the two characters together, the two pairs of contrasting characters independently assort during the formation of the gametes, producing distinct traits in the F2 generation.

Similarities Between Monohybrid and Dihybrid Inheritance

• Monohybrid and dihybrid inheritance are two types of inheritance patterns.
• Both obey the Mendelian inheritance.
• Homozygous parents are used in both types of crosses.
• F1 generation exhibits only dominant phenotypes.

Difference Between Monohybrid and Dihybrid Inheritance

Definition

Monohybrid inheritance refers to the inheritance of a single allele pair while dihybrid inheritance refers to the the inheritance of two, independent allele pairs.

Defined by

Further, monohybrid inheritance is defined in Mendel’s first law while the dihybrid inheritance is defined in Mendel’s second law.

Phenotypic Ratio of the F2 Generation

The phenotypic ratio of the F2 generation is 3:1 in monohybrid cross while the phenotypic ratio of the F2 generation is 9:3:3:1.

Genotypic Ration of the F2 Generation

The genotypic ratio of F2 generation in the monohybrid cross is 1:2:1 while the genotypic ratio of F2 generation in the dihybrid cross is 1:2:1:2:4:2:1:2:1.

Importance

Monohybrid inheritance is used to study the pattern of inheritance during the first and second generation offspring while dihybrid inheritance is used to study the inheritance pattern of dominant and recessive characters for two different traits.

Conclusion

Monohybrid inheritance describes the inheritance of a single allele pair, which gives 3:1 phenotypic ratio while dihybrid inheritance describes the inheritance of two, independent allele pairs, giving the 9:3:3:1 phenotypic ratio. The main difference between monohybrid and dihybrid inheritance is the number of allele pairs involved and the phenotypic ratios of the F2 generation.

Reference:

1. “Monohybrid Inheritance.” TutorVista.com, Available Here
2. “Dihybrid Inheritance.” TutorVista.com, Available Here

Image Courtesy:

1. “Figure 12 02 02” By CNX OpenStax (CC BY 4.0) via Commons Wikimedia   
2. “Figure 12 03 02” By CNX OpenStax (CC BY 4.0) via Commons Wikimedia

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