Genetics I Mendalism I by Dr. S.K. MEHTA SIR

Mendelianism refers to the principles of heredity first outlined by Gregor Mendel in the mid-19th century. Mendel, an Austrian monk, conducted experiments with pea plants and formulated foundational laws of inheritance. These principles are the basis for classical genetics and are summarized in the following key concepts:

Law of Segregation: This principle states that each individual has two alleles for each gene, one inherited from each parent. These alleles separate during gamete formation, and each gamete receives only one allele. When fertilization occurs, the offspring inherit one allele from each parent.

Law of Independent Assortment: Mendel's second law states that the alleles for different traits are distributed independently of each other into gametes. This means that the inheritance of one trait (e.g., flower color) does not influence the inheritance of another trait (e.g., seed shape), provided the genes are on different chromosomes.

Law of Dominance: According to this principle, when two different alleles for a gene are present, one may be dominant and the other recessive. The dominant allele is expressed in the phenotype, while the recessive allele is masked unless the individual is homozygous recessive for that gene.

Genotype and Phenotype: Mendel’s work also established the distinction between genotype (the genetic makeup of an organism) and phenotype (the physical expression of the genotype). Different combinations of alleles result in different phenotypic traits.

Punnett Squares: Mendelian principles can be illustrated using Punnett squares, which are diagrams used to predict the genotypes and phenotypes of offspring from genetic crosses.

Mendelianism laid the groundwork for modern genetics, although later discoveries have expanded and refined these principles. For instance, Mendelian inheritance is often modified by factors such as gene linkage, incomplete dominance, and codominance.

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