Question

Describe Mendel's Laws.

Hint:

Mendel’s laws apply to traits controlled by single genes with clear dominant and recessive alleles. More complex inheritance patterns, such as co-dominance and polygenic inheritance, occur in nature.

Answer 1

Mendel's laws of inheritance are the foundation of classical genetics. They describe how traits are inherited from one generation to the next. These laws are based on Mendel's experiments with pea plants. There are three main laws:
1. Law of Dominance:
This law states that in a heterozygous organism, the dominant allele will express its trait, while the recessive allele will be masked. In simple terms, when two different alleles are present, the dominant one will determine the organism’s appearance.
Example: In pea plants, the allele for round seeds (R) is dominant over the allele for wrinkled seeds (r). Therefore, a plant with the genotype Rr will have round seeds. \[ \text{R (Round seed)}>\text{r (Wrinkled seed)} \]
2. Law of Segregation:
This law states that every organism possesses two alleles for each trait, one inherited from each parent. These alleles segregate (separate) during the formation of gametes (egg and sperm), so each gamete carries only one allele for each trait.
Example: In a cross between two heterozygous pea plants (Rr), the offspring can inherit either the R or r allele from each parent. \[ \text{Gametes:} R \text{ or } r \] \[ \text{Resulting Genotypes:} 1 \, \text{RR} : 2 \, \text{Rr} : 1 \, \text{rr} \]
3. Law of Independent Assortment:
This law states that genes for different traits are inherited independently of one another, provided they are located on different chromosomes. This means the inheritance of one trait does not affect the inheritance of another trait.
Example: In a dihybrid cross between two heterozygous pea plants (RrYy × RrYy), the traits for seed shape (R/r) and seed color (Y/y) assort independently. \[ \text{Possible Gametes:} \text{RY, Ry, rY, ry} \] \[ \text{F2 Generation Phenotypic Ratio:} 9:3:3:1 \]
Conclusion:
Mendel's laws of inheritance laid the foundation for our understanding of genetics. These laws explain how traits are passed from parents to offspring and how genetic variation arises in populations.