Question

Explain Mendel's monohybridization experiment. Write the rules proposed on the basis of this experiment. Draw its diagram using punnet square.

Answer 1

Mendel carried out his key experiments using the garden pea, Pisum sativum, as a model system. Pea plants make a convenient system for studies of inheritance. Useful features of peas include their rapid life cycle and the production of lots and lots of seeds. Pea plants also self-fertilize, meaning that the same plant makes both the sperm and the egg. Mendel took advantage of this property to produce true-breeding pea lines. Pea plants are also easy to cross or mate in a controlled way.

First, he crossed one true-breeding parent to another. The plants used in this initial cross are called the P generation, or parental generation. Mendel crossed a pure-breeding round-seeded variety with a pure-breeding wrinkled-seeded one. He collected the seeds from the P generation cross and grew them up. These offspring were called the F1 generation, short for the first filial generation. All the peas produced in the second or hybrid generation were round. Mendel then allowed his hybrid peas to self-pollinate. The wrinkled trait which had disappeared in his hybrid generation — reappeared in 25% of the new crop of peas. Mendel's experiments extended beyond the F2 generation to F3, F4 and later generations, but his model of inheritance was based mostly on the first three generations.

Mendel proposed the following laws on the basis of his experiments:

1) Law of segregation ("First Law")- During gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene.

2) Law of independent assortment ("Second Law")- Genes for different traits can segregate independently during the formation of gametes.

3) Law of dominance ("Third Law")- Some alleles are dominant while others are recessive; an organism with at least one dominant allele will display the effect of the dominant allele.