Monohybrid and Dihybrid inheritance - SS3 Biology Lesson Note

Monohybrid and dihybrid inheritance are patterns of inheritance that describe how traits are transmitted from parents to offspring. Let's explore each type of inheritance:

1.       Monohybrid Inheritance: Monohybrid inheritance refers to the inheritance of a single trait controlled by a single gene. In this type of inheritance, individuals differ in one specific characteristic, such as flower colour or seed shape. Each parent contributes one allele for that trait to their offspring.

To illustrate monohybrid inheritance, let's consider the example of flower colour in pea plants studied by Gregor Mendel. Pea plants can have either purple flowers (dominant trait) or white flowers (recessive trait). When a purple-flowered plant (homozygous dominant) is crossed with a white-flowered plant (homozygous recessive), the first-generation offspring, known as the F1 generation, all have purple flowers. However, when these F1 plants are crossed with each other, the second-generation offspring, known as the F2 generation, exhibit a 3:1 phenotypic ratio, with approximately 75% having purple flowers and 25% having white flowers. This outcome demonstrates the segregation and independent assortment of alleles according to Mendel's laws.

2.       Dihybrid Inheritance: Dihybrid inheritance involves the inheritance of two different traits controlled by two different genes. The traits are located on separate chromosomes or are far apart on the same chromosome, allowing for independent assortment. In dihybrid crosses, the inheritance patterns of two traits are simultaneously analysed.

Continuing with Mendel's work, he performed experiments involving two traits in pea plants: seed colour (yellow or green) and seed texture (smooth or wrinkled). Mendel crossed plants that were pure-breeding for each trait (homozygous) and observed the inheritance of both traits in the offspring. He found that the F1 generation exhibited a phenotypic ratio of 9:3:3:1, meaning that 9 individuals showed both dominant traits, 3 showed one dominant and one recessive trait, 3 showed the other dominant and one recessive trait, and 1 showed both recessive traits.

This 9:3:3:1 ratio occurs due to the independent assortment of alleles for the two traits during gamete formation. Each trait segregates independently, following Mendel's law of independent assortment.

Monohybrid and dihybrid inheritance are important concepts in genetics, providing a basis for understanding how traits are inherited and how genetic variation arises in populations. These principles, established by Mendel's experiments, laid the groundwork for the development of modern genetics.

(docsity.com)