PAGE 129 – In-text Questions (Answered)

Q1. 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 is likely to have arisen earlier?

Answer:

Trait B is likely to have arisen earlier because:

• In asexually reproducing organisms, traits spread only by DNA copying

• A trait present in more individuals (60%) has had more generations to spread

• So trait B must have appeared before trait A

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Q2. How does the creation of variations in a species promote survival?

Answer:

Variations help species survive by:

• Allowing some individuals to withstand environmental changes

• Helping organisms adapt to climate, food availability, and diseases

• Increasing chances of survival in natural selection

Example:

Bacteria resistant to heat survive a heat wave, others die → resistant type survives and continues the species.

PAGE 133 – In-text Questions (Answered)

Q1. How do Mendel’s experiments show that traits may be dominant or recessive?

Answer:

Mendel crossed tall pea plants with short pea plants:

• F₁ generation → all plants were tall

• F₂ generation → 3 tall : 1 short

This shows:

• Tall trait (T) is dominant

• Short trait (t) is recessive

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Q2. How do Mendel’s experiments show that traits are inherited independently?

Answer:

When Mendel crossed:

• Tall round (T R) × short wrinkled (t r)

He found in F₂ generation 4 types of plants:

• Tall round

• Tall wrinkled

• Short round

• Short wrinkled

This shows seed shape and plant height are inherited independently.

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Q3. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?

Answer:

No, this is not enough information because:

• Blood group A can be AA or AO

• For the child to have O blood group, both parents must pass O allele

• So the father must be AO

• We cannot conclude dominance because we only know inheritance pattern, not relative strength

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Q4. How is the sex of the child determined in human beings?

Answer:

Sex is determined by father’s chromosome:

• Mother always contributes X chromosome

• Father contributes X or Y

So the father determines the sex of the child.