Notes from NEET topper
Law Of Segregation
The Law of Segregation is one of Gregor Mendel’s fundamental principles of inheritance, and it describes how alleles (different forms of a gene) segregate or separate during the formation of gametes (sperm and egg cells). This law is based on Mendel’s experiments with pea plants and can be summarized as follows:
1. Allele Pairs:
For each inherited trait, an organism has two alleles, one inherited from each parent.
These two alleles may be the same (homozygous) or different (heterozygous).
2. Allele Separation:
During the formation of gametes (sperm and egg cells) through the process of meiosis, the two alleles segregate from each other.
This means that one allele goes into one gamete, and the other allele goes into another gamete.
As a result, each gamete carries only one allele for a specific trait.
3. Random Assortment:
The separation of alleles into gametes is random and independent for each trait.
The segregation of alleles for one trait does not influence the segregation of alleles for another trait.
This principle is known as the Law of Independent Assortment and applies when genes are located on different chromosomes.
4. Genotype and Phenotype:
The genotype of an organism refers to the combination of alleles it possesses for a particular trait.
The phenotype of an organism refers to the observable trait resulting from the expression of those alleles.
The alleles an individual inherits will determine its genotype, and the genotype will, in turn, determine its phenotype.
Example:
Mendel’s experiments with pea plants included the study of flower color.
He had two alleles for flower color: one for purple flowers (P) and one for white flowers (p).
When a plant had two identical alleles (homozygous), its genotype was either PP (purple flowers) or pp (white flowers).
When a plant had two different alleles (heterozygous), its genotype was Pp.
During the formation of gametes, the alleles separated. For example, in a Pp plant, the P allele went into some gametes, and the p allele went into others.
When Pp plants were allowed to self-pollinate, the resulting F2 generation exhibited the 3:1 phenotypic ratio (3 purple flowers to 1 white flower) predicted by Mendel’s Law of Segregation.
