Ans: Mendelian inheritance, also known as Mendelian genetics, refers to the fundamental principles of how specific traits are inherited from one generation to the next. These principles were first described by Gregor Mendel, in the mid-19th century, based on his experiments with pea plants. Mendel’s work laid the foundation for our understanding of heredity and genetics. There are three key principles of Mendelian inheritance:
a). Law of Segregation:
Each individual has two alleles (gene variants) for each gene, one inherited from each parent. During the formation of gametes (sperm and egg cells), these two alleles segregate or separate from each other, such that each gamete carries only one allele.
This means that when two gametes fuse during fertilization, the offspring will inherit one allele from each parent, restoring the diploid number of alleles.
Example: If an individual carries two alleles for flower color in pea plants (one for purple flowers and one for white flowers), these alleles will segregate during gamete formation. As a result, half of the gametes will carry the purple allele, and the other half will carry the white allele.
b).Law of Independent Assortment:
Genes for different traits (located on different chromosomes) assort independently of each other during gamete formation.
This means that the inheritance of one gene does not affect the inheritance of another gene, and the assortment of alleles for one trait is not influenced by the assortment of alleles for another trait.
Example: If Mendel studied two traits in pea plants, such as flower color and seed shape, the alleles for flower color (e.g., purple or white) would segregate independently of the alleles for seed shape (e.g., round or wrinkled).
c). Dominance and Recessiveness:
Some alleles are dominant, and others are recessive.
Dominant alleles are expressed as traits when present in a heterozygous individual (one dominant and one recessive allele).
Recessive alleles are only expressed as traits when present in a homozygous recessive individual (two recessive alleles).
Example: In Mendel’s pea plant experiments, the allele for purple flower color was dominant (P), and the allele for white flower color was recessive (p). If an individual had the genotype PP or Pp, they would have purple flowers because the dominant allele (P) masks the expression of the recessive allele (p). Only individuals with the genotype pp would have white flowers.