Q1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as:

(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw

Correct Answer: (c) TtWW

Detailed Explanation:

• The tall plant crossed with short plant produced progeny where all flowers were violet.
  → This means violet (W) is dominant over white (w), and the tall parent must have two dominant alleles W W, since no white appeared in F₁.

• In the same cross, almost half of the plants were short.
  → For short plants to appear, the tall parent must carry the recessive gene t along with dominant T, so when crossed with short plant (tt), some offspring receive t and become short.

Thus, tall parent genotype =

$$TtWW$$

---

Q2. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. Can we say light-eye colour is dominant or recessive? Why or why not?

Answer:

No, we cannot conclude whether light-eye colour is dominant or recessive based on the information given.

Detailed Explanation:

• The fact that parents and children both show the same trait only proves that the trait is inherited, not whether it is dominant or recessive.

• To determine dominance, we need to study trait expression over multiple generations, including:

  • Crosses between mixed-trait parents

  • Occurrence of traits in grandchildren or siblings

For example, only if light-eyed children appear even when one parent has dark eyes, we could infer dominance.
Here, we don’t have enough evidence.

---

Q3. Outline a project which aims to find the dominant coat colour in dogs.

Expanded Project Outline:

1. Observe and Record

   • Visit households or shelters where dogs have different coat colours.

   • Record the colours of parents and their puppies in a chart.

2. Collect Data

   • Note which colour is more frequent in the offspring from mixed-colour parents.

3. Create Possible Crosses

   • Example: Black × Brown → Puppies mostly black?

   • Repeat with several families for reliability.

4. Analyze Results

   • If one colour consistently appears more often in puppies, even when parents are mixed, that colour is dominant.

Conclusion

• The colour that masks the other in offspring is dominant.

---

Q4. How is the equal genetic contribution of male and female parents ensured in the progeny?

Detailed Answer:

• Humans have 23 pairs (46) chromosomes in body cells.

• During gamete formation (sperms and eggs), the number becomes 23 (half) due to meiosis.

• During fertilisation:

  $$$$

23 (father) + 23 (mother) = 46   (zygote)
]

• Thus both parents contribute equally to the genetic makeup of the child.

• Each parent provides one set of chromosomes, ensuring equal hereditary information.

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

---

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

---

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.

---

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

---

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.