CBSE Class 10 Answered

• Mendelian experiments suggest that during sexual reproduction, fusion of gametes takes place. Each parent of the parental generation P₁ contributes equally a copy of the same gene to the DNA of the progeny. Each pea plant has 2 sets of every gene called alleles, one received from the male parent and the other from the female parent. But each gamete has only one gene set.
• In a dihybrid cross, if the progeny inherited only one gene set from each parent, then the two traits in Mendel’s experiment, namely shape and colour of the seed would co-exist. But this does not happen because each gene set is not present as a single long thread of DNA, but as separate independent pieces called chromosomes.
• In human beings, there are 46 chromosomes or 23 pairs of chromosomes, one from each parent. During gamete formation, the gamete takes one chromosome from each pair. When two such gametes having a single set of genes combine together, they restore the normal diploid number of chromosomes in the progeny. This is the mechanism of inheritance of traits. The results of Mendel’s experiments can be explained by this mechanism.

Basic features of mechanism of inheritance of traits:

• Characters are controlled by genes.
• Each gene controls only one character.
• There may be two or more forms of a particular gene.
• One form of the gene may be dominant over the other form.
• Genes are present on chromosomes.
• An individual bears two forms of a gene, either similar or dissimilar.
• The two forms of the gene separate independently during gamete formation.
• The two forms of the gene are brought together during zygote formation.