Class XII Biology
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519 questions in this chapter
Question 31 of 519
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If a heterozygous tall pea plant (Tt) is self-pollinated, what will be the ratio of tall to dwarf plants in the offspring?
Answer: (c) 3 : 1
Explanation: When a heterozygous tall pea plant (Tt) is self-pollinated, the genotypes formed are TT, Tt, and tt in the ratio 1 : 2 : 1.
Since both TT and Tt produce tall plants, the phenotypic ratio of tall to dwarf is 3 : 1.
Question 32 of 519
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When a red-flowered snapdragon (RR) is crossed with a white-flowered snapdragon (rr), the Fâ generation has pink flowers. This is an example of:
Answer: (b) Incomplete dominance
Explanation: In incomplete dominance, neither allele is completely dominant over the other.
In snapdragon (Antirrhinum majus), crossing red (RR) and white (rr) results in pink (Rr) flowers, showing an intermediate phenotype.
Question 33 of 519
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Haemophilia is an example of a:
Answer: (d) Sex-linked recessive disorder
Explanation: Haemophilia is caused by a mutation in a gene present on the X chromosome.
Since males have only one X chromosome (XY), the presence of the defective gene causes the disease.
Females (XX) are usually carriers because a normal allele on the other X can compensate.
The disorder leads to delayed clotting of blood due to deficiency of clotting factors.
Question 34 of 519
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A mutation that arises due to a change in a single base pair of DNA is known as a:
A change in a single base pair of DNA is known as a point mutation. A classical example is sickle cell anemia.
Question 35 of 519
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Physical or chemical factors that induce mutations are referred to as:
There are many chemical and physical factors that induce mutations, and these are referred to as mutagens. UV radiation is given as an example of a mutagen.
Question 36 of 519
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The analysis of traits in several generations of a family using a family tree is called:
The study of family history about the inheritance of a particular trait is called pedigree analysis, where the inheritance of a trait is represented in the family tree over generations.
Question 37 of 519
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Genetic disorders that are mainly determined by alteration or mutation in a single gene are called:
Mendelian disorders are mainly determined by alteration or mutation in a single gene. Their inheritance pattern can be traced using pedigree analysis.
Question 38 of 519
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Colour blindness is a:
Colour blindness is a sex-linked recessive disorder caused by a mutation in certain genes present on the X chromosome.
Question 39 of 519
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Which of the following disorders is a sex-linked recessive disease where a single protein involved in blood clotting is affected?
Haemophilia is a sex linked recessive disease in which a single protein that is part of the cascade of proteins involved in the clotting of blood is affected, resulting in non-stop bleeding from a simple cut.
Question 40 of 519
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Sickle-cell anaemia is an:
Sickle-cell anaemia is an autosome linked recessive trait that can be transmitted from parents to the offspring when both partners are carriers for the gene.
