Principles of Inheritance and Variation

Which one of the following statements regarding chromosomal disorders is correct?

1. Down syndrome is caused by monosomy of chromosome 21.
2. Turner's syndrome occurs due to the absence of one X chromosome.
3. Klinefelter's syndrome occurs in individuals having 44 + XY chromosomes.
4. Down syndrome results from mutation in mitochondrial DNA.

A woman with blood group A and genotype IAi marries a man with blood group B and genotype IBi. Which blood group cannot appear among their children?

1. Blood group A
2. Blood group B
3. Blood group AB
4. None of these

Thomas Hunt Morgan's experiments on Drosophila melanogaster provided strong evidence for:

1. Artificial selection
2. Linkage and genetic recombination
3. Natural selection only
4. Mutation theory only

Colour blindness in humans is inherited as:

1. Autosomal dominant trait
2. Autosomal recessive trait
3. X-linked recessive trait
4. Y-linked trait

Which one of the following statements correctly explains Mendel's Law of Dominance?

1. Both alleles of a gene are equally expressed in the F1 generation.
2. One allele masks the expression of the other allele in a heterozygous condition.
3. Alleles always assort independently during gamete formation.
4. Recessive alleles disappear permanently after the F1 generation.

Sickle-cell anaemia is caused by the substitution of:

1. Valine by glutamic acid at the sixth position of the beta-globin chain
2. Glutamic acid by valine at the sixth position of the beta-globin chain
3. Glycine by alanine at the first position of the alpha-globin chain
4. Lysine by arginine at the eighth position of the beta-globin chain

The phenomenon in which a single gene influences more than one phenotypic character is known as:

1. Polygenic inheritance
2. Multiple allelism
3. Pleiotropy
4. Codominance

Haemophilia is inherited as a:

1. Autosomal dominant trait
2. Autosomal recessive trait
3. X-linked recessive trait
4. Y-linked trait

The human ABO blood group system is an example of:

1. Incomplete dominance only
2. Codominance and multiple alleles
3. Polygenic inheritance
4. Sex-linked inheritance

In snapdragon (Antirrhinum), a cross between a red-flowered plant and a white-flowered plant produces pink-flowered offspring in the F1 generation. This is an example of:

1. Complete dominance
2. Codominance
3. Incomplete dominance
4. Multiple alleles

In a test cross involving a heterozygous individual, the unknown genotype is crossed with:

1. Homozygous dominant
2. Heterozygous dominant
3. Homozygous recessive
4. Homozygous codominant

The Law of Independent Assortment is applicable only when the genes are:

1. Located on the same chromosome very close together
2. Completely linked
3. Located on different chromosomes or far apart on the same chromosome
4. Present only in bacteria

Which of the following correctly represents the phenotypic ratio obtained in Mendel's dihybrid cross?

1. 3 : 1
2. 1 : 2 : 1
3. 9 : 3 : 3 : 1
4. 1 : 1 : 1 : 1

Mendel's Law of Segregation states that:

1. Genes located on the same chromosome always remain together.
2. Two alleles of a gene separate during gamete formation.
3. Dominant genes always increase in number.
4. Recessive genes disappear after one generation.

In a monohybrid cross between two heterozygous pea plants (Tt × Tt), what is the probability of obtaining a homozygous recessive offspring?

1. 1/2
2. 1/4
3. 3/4
4. 1/8