(a) What is the law of dominance of traits? Explain with an example.

(b) Why are the traits acquired during the life time of an individual not inherited? Explain.

(a) Law of Dominance of Traits

The Law of Dominance states that when two contrasting alleles (versions of a gene) for a trait are present together in an organism (heterozygous state), only one allele expresses itself physically. This expressed trait is called the dominant trait, while the unexpressed allele is called the recessive trait. A single copy of the dominant allele (e.g., '$T$') is sufficient to express the dominant characteristic, whereas two copies of the recessive allele (e.g., '$tt$') must be present for the recessive characteristic to be expressed.

Example:

• Mendel crossed a pure tall pea plant ($TT$) with a short pea plant ($tt$).
• In the first generation ($F_1$ progeny), all the plants obtained were tall ($Tt$). There were no medium-height plants.
• This demonstrates that even though the $F_1$ plants inherited both the tallness factor ($T$) and the shortness factor ($t$), only the tallness trait was expressed. Therefore, tallness is the dominant trait and shortness is the recessive trait.

---

(b) Why Acquired Traits are Not Inherited

Traits acquired by an individual during their lifetime (such as learning a skill, developing muscles, or losing a body part due to injury) are not passed on to the next generation because:

1. Somatic vs. Germ Cells: Acquired traits only bring about changes in the non-reproductive tissues (somatic cells) of the body. They do not alter the DNA of the reproductive cells (germ cells/gametes).
2. Mechanism of Heredity: As explained in the text, cellular DNA is the information source for making proteins, and traits are determined by genes. During sexual reproduction, both parents contribute genetic material specifically through their germ cells (sperm and egg), which carry a single set of chromosomes.
3. No DNA Alteration: Since acquired experiences or physical changes do not alter the genetic code (DNA sequence) inside the germ cells, these changes cannot be transmitted to the progeny. Thus, only inherited traits (encoded in the DNA of germ cells) are passed on.