NCERT Solutions for Class 10th Science Chapter 8 Heredity

Trait B must have appeared earlier.
This is because in asexually reproducing organisms, traits spread very slowly. Since Trait B is found in 60% of the population and Trait A only in 10%, the trait that is present in more individuals must have been there for a longer time.

So, Trait B arose earlier than Trait A.

Variations help a species survive because they make some individuals better suited to changes in the environment.
If the climate changes, food becomes less, or a new disease appears, not all individuals will be affected in the same way.
Those with useful variations will survive and reproduce, while others may die.

So, variations increase the chances that at least some members of the species will survive, even when conditions change.

Mendel crossed a tall plant with a short plant. All the plants in the first generation were tall. This means the tall trait hides the short trait.
When these tall plants were crossed again, the short plants came back in the next generation.
This showed that:
Tall trait = dominant (shows itself)
Short trait = recessive (gets hidden but is not lost)
So Mendel proved that some traits hide others, which is why they are called dominant and recessive.

Mendel crossed plants with two different traits and found new combinations in the next generation.
Traits like seed shape and seed colour got mixed in different ways.
This showed that each trait is inherited independently of the other.

No, this information is not enough to tell which blood group is dominant.
The father could be AA or AO, and the mother is OO, so the child can get O only if the father has an O gene (AO).

So we cannot decide dominance just from this one family — we need more crosses to be sure.

In humans, the mother always gives an X chromosome. The father can give either an X or a Y chromosome.
If the father gives X, the child is girl (XX).
If the father gives Y, the child is boy (XY).

So, the sex of the child is determined by the father.

Short parent = ttww (short + white)
All progeny have violet flowers, so the tall parent must give a W to every child → therefore the tall parent must be WW.
Almost half of the progeny are short, which means the tall parent must be Tt (so it can give t to some children).

So the tall parent’s genotype = TtWW
Correct option: (c) TtWW

No, we cannot say whether light eye colour is dominant or recessive.
Children often resemble their parents, but this does not tell us which trait is stronger.
To know dominance or recessiveness, we need controlled crosses or more detailed genetic information, not just observation.

During reproduction, both parents produce gametes (sperm and egg) that contain half the number of chromosomes.
When the sperm and egg fuse during fertilisation, the child gets half the genes from the father and half from the mother.
This ensures equal genetic contribution from both parents in the progeny.