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:
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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 =
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:
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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.
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To determine dominance, we need to study trait expression over multiple generations, including:
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Crosses between mixed-trait parents
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Occurrence of traits in grandchildren or siblings
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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:
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Observe and Record
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Visit households or shelters where dogs have different coat colours.
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Record the colours of parents and their puppies in a chart.
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Collect Data
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Note which colour is more frequent in the offspring from mixed-colour parents.
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Create Possible Crosses
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Example: Black × Brown → Puppies mostly black?
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Repeat with several families for reliability.
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Analyze Results
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If one colour consistently appears more often in puppies, even when parents are mixed, that colour is dominant.
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Conclusion
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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:
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Humans have 23 pairs (46) chromosomes in body cells.
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During gamete formation (sperms and eggs), the number becomes 23 (half) due to meiosis.
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During fertilisation:
23 (father) + 23 (mother) = 46 (zygote)
]
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Thus both parents contribute equally to the genetic makeup of the child.
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Each parent provides one set of chromosomes, ensuring equal hereditary information.