Heredity
This chapter covers how traits are inherited from parents to offspring, Mendel's laws of inheritance based on his experiments with pea plants, and how sex is determined in humans.
Heredity is the passing of genetic characteristics (traits) from parents to their offspring through genes, which are segments of DNA that carry the information for a particular trait.
Mendel crossed tall (TT) and short (tt) pea plants. The first generation (F1) was all tall, showing tallness is dominant. When F1 plants were self-pollinated, the F2 generation showed a 3:1 ratio of tall to short plants, revealing that the short trait (recessive) was hidden but not lost in F1.
Q. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait would have arisen earlier?
Trait B, since it is present in a larger percentage of the population, it must have arisen earlier, giving it more time to spread through the population via reproduction.
In human beings, all men and women have 22 pairs of autosomes. Women have XX sex chromosomes while men have XY. The sex of a child is determined by whether the father's sperm carries an X or a Y chromosome.
Q. How do Mendel's experiments show that traits are inherited independently?
In Mendel's dihybrid cross (round-yellow seeds crossed with wrinkled-green seeds), the F2 generation showed new combinations like round-green and wrinkled-yellow seeds in addition to the parental types, proving that the genes for seed shape and seed colour assort independently of each other.
A child receiving an X chromosome from the father will develop into a:
Correct answer: (B) Girl
A cross between two pea plants that are heterozygous for one trait is called a _______ cross.
Monohybrid
The mother's chromosomes determine whether a child will be a boy or a girl.
False — the mother always contributes an X chromosome, so it is the father's chromosome (X or Y) that determines the sex of the child.