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Principles of Inheritance & Variation – Mendel, Multiple Alleles, Polygenic, Chromosomal Theory Quiz - ICSE Class 12 Biology

Free practice quiz: Principles of Inheritance & Variation – Mendel, Multiple Alleles, Polygenic, Chromosomal Theory (ICSE Class 12 Biology). 116 multiple-choice questions with answers and explanations. Play online, no sign-up needed.

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  1. In a dihybrid cross between two heterozygous parents for two independently assorting genes, what is the phenotypic ratio of the offspring if incomplete dominance is observed at both loci?

    1. 9:3:3:1
    2. 1:2:1:2:4:2:1:2:1
    3. 3:1
    4. 1:1:1:1
    Show answer

    Answer: B. 1:2:1:2:4:2:1:2:1

    When incomplete dominance occurs at two loci for independently assorting genes, the phenotypic ratio for each gene is 1:2:1. To find the combined phenotypic ratio for both genes, we multiply the individual ratios. (1:2:1) x (1:2:1) = 1(AABB) : 2(AABb) : 1(AAbb) : 2(AaBB) : 4(AaBb) : 2(Aabb) : 1(aaBB) : 2(aaBb) : 1(aabb). This expands to the genotypic classes which, with incomplete dominance, directly correspond to distinct phenotypes.

  2. If a chromosome undergoes a deletion, the result is:

    1. A loss of genetic material.
    2. A change in the position of a chromosome segment.
    3. A repetition of genetic material.
    4. A reversal of a chromosome segment.
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    Answer: A. A loss of genetic material.

    A deletion is a type of chromosomal mutation where a segment of a chromosome is lost or removed. This results in a net loss of genetic material. Translocation involves the movement of a segment to a non-homologous chromosome. Inversion involves reattachment in reverse order. Duplication involves repetition of a segment.

  3. A chromosomal mutation where a segment of a chromosome is lost is called:

    1. Inversion
    2. Duplication
    3. Translocation
    4. Deletion
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    Answer: D. Deletion

    A deletion is a chromosomal mutation that results in the loss of a segment of a chromosome and, therefore, the loss of genetic material. Inversion involves a reversal of a segment within the same chromosome. Duplication is the repetition of a chromosome segment. Translocation involves the movement of a chromosome segment to a non-homologous chromosome.

  4. Which of the following is a characteristic of quantitative traits?

    1. They are determined by a single gene with two alleles.
    2. They show discrete, distinct phenotypic categories.
    3. They are influenced by multiple genes and environmental factors.
    4. They always exhibit complete dominance.
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    Answer: C. They are influenced by multiple genes and environmental factors.

    Quantitative traits, such as height, weight, or skin color, are influenced by the additive effects of multiple genes (polygenes) and often by environmental factors. This results in a continuous variation of phenotypes, rather than discrete categories. Traits determined by a single gene are typically Mendelian and show distinct categories.

  5. In a population in Hardy-Weinberg equilibrium, if the frequency of the allele 'A' is 0.4, what is the frequency of the homozygous recessive genotype 'aa'?

    1. 0.16
    2. 0.36
    3. 0.48
    4. 0.64
    Show answer

    Answer: B. 0.36

    In Hardy-Weinberg equilibrium, if the frequency of the dominant allele 'A' (p) is 0.4, then the frequency of the recessive allele 'a' (q) is p + q = 1. So, q = 1 - p = 1 - 0.4 = 0.6. The frequency of the homozygous recessive genotype 'aa' is represented by q^2. Therefore, the frequency of 'aa' is (0.6)^2 = 0.36.

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