Principles of Inheritance

1. All genes located on the same chromosome:

a. Form different groups depending upon their relative distance

b. Form one linkage group

c. Will not from any linkage groups

d. Form interactive groups

Answer: b

Explanation: All genes located on a single chromosome are physically connected to one another and tend to be inherited together. Therefore, they collectively constitute a single linkage group.

2. Conditions of a karyotype 2n + 1, 2n - 1 and 2n + 2, 2n - 2 are called:

a. Aneuploidy

b. Polyploidy

c. Allopolyploidy

d. Monosomy

Answer: a

Explanation: Aneuploidy refers to a chromosomal abnormality where an organism has an abnormal number of chromosomes (extra or missing) due to the non-disjunction of chromatids during cell division. Examples include trisomy (2n+1) and monosomy (2n-1).

3. Distance between the genes and percentage of recombination shows:

a. A direct relationship

b. An inverse relationship

c. A parallel relationship

d. No relationship

Answer: a

Explanation: Crossing over occurs more frequently between genes that are situated far apart on a chromosome. Therefore, as the physical distance between two linked genes increases, the percentage of recombination between them also directly increases.

4. If a genetic disease is transferred from a phenotypically normal but carrier female to only some of the male progeny, the disease is:

a. Autosomal dominant

b. Autosomal recessive

c. Sex-linked dominant

d. Sex-linked recessive

Answer: d

Explanation: In a sex-linked recessive disorder (like haemophilia), a carrier female (XX') passes the defective X chromosome to 50% of her sons, who will express the disease since males only have one X chromosome. Her daughters will either be normal or carriers.

5. In sickle cell anaemia glutamic acid is replaced by valine. Which one of the following triplets codes for valine?

a. GGG

b. AAG

c. GAA

d. GUG

Answer: d

Explanation: Sickle cell anaemia is caused by a point mutation where the codon GAG (which codes for glutamic acid) is mutated to GUG on the mRNA. The new GUG codon translates to the amino acid valine.

6. Person having genotype $I^{A}I^{B}$ would show the blood group as AB. This is because of:

a. Pleiotropy

b. Co-dominance

c. Segregation

d. Incomplete dominance

Answer: b

Explanation: The $I^{A}$ and $I^{B}$ alleles are co-dominant, meaning neither allele completely masks the other. When both are present in an individual's genotype, both distinct surface antigens (A and B) are fully expressed on the red blood cells.

7. ZZ/ZW type of sex determination is seen in:

a. Platypus

b. Snails

c. Cockroach

d. Peacock

Answer: d

Explanation: In birds, such as the peacock, sex determination follows the ZZ/ZW system. The males are homogametic (ZZ) and the females are heterogametic (ZW), meaning the female's egg determines the sex of the offspring.

8. A cross between two tall plants resulted in offspring having few dwarf plants. What would be the genotypes of both the parents?

a. TT and Tt

b. Tt and Tt

c. TT and TT

d. Tt and tt

Answer: Tt and Tt (Heterozygous)

Explanation: For two tall plants to produce dwarf offspring (a recessive trait, tt), both parents must carry the recessive allele hidden behind the dominant tall allele. Thus, both parents must be heterozygous (Tt).

9. In a dihybrid cross, if you get 9:3:3:1 ratio it denotes that:

a. The alleles of two genes are interacting with each other

b. It is a multigenic inheritance

c. It is a case of multiple allelism

d. The alleles of two genes are segregating independently.

Answer: d

Explanation: The classic 9:3:3:1 phenotypic ratio in the F2 generation is the hallmark of Mendel's Law of Independent Assortment. It indicates that the alleles for the two distinct traits separate and combine independently of one another during gamete formation.

10. Which of the following will not result in variations among siblings?

a. Independent assortment of genes

b. Crossing over

c. Linkage

d. Mutation

Answer: c

Explanation: Linkage is the tendency of genes located closely together on the same chromosome to be inherited together without separating. Because it prevents new recombinant gene combinations, strong linkage reduces genetic variation among offspring.

11. Mendel's Law of independent assortment holds good for genes situated on the:

a. Non-homologous chromosomes

b. Homologous chromosomes

c. Extra nuclear genetic element

d. Same chromosome

Answer: a

Explanation: Independent assortment occurs because non-homologous chromosomes align and separate randomly during meiosis. Genes situated on the same chromosome (linked genes) generally do not assort independently unless separated by crossing over.

12. Occasionally, a single gene may express more than one effect. The phenomenon is called:

a. Multiple allelism

b. Mosaicism

c. Pleiotropy

d. Polygeny

Answer: c

Explanation: Pleiotropy occurs when a single gene influences multiple, seemingly unrelated phenotypic traits. A classic example is the gene for phenylketonuria, which causes mental retardation as well as a reduction in hair and skin pigmentation.

13. In a certain taxon of insects some have 17 chromosomes and the others have 18 chromosomes. The 17 and 18 chromosome-bearing organisms are:

a. Males and females, respectively

b. Females and males, respectively

c. All males

d. All females

Answer: a

Explanation: This describes the XO type of sex determination seen in many insects (like grasshoppers). Females have a pair of X chromosomes (XX = 18 total), while males have only one X chromosome (XO = 17 total).

14. The inheritance pattern of a gene over generations among humans is studied by the pedigree analysis. Character studied in the pedigree analysis is equivalent to:

a. Mendelian trait

b. Polygenic trait

c. Quantitative trait

d. Maternal trait

Answer: a

Explanation: Pedigree analysis is specifically used to track the inheritance of single-gene disorders over multiple generations. These traits follow classical Mendelian principles of dominant and recessive inheritance.

15. It is said that Mendel proposed that the factor controlling any character is discrete and independent. His proposition was based on the:

a. Observations that the offspring of a cross made between the plants having two contrasting characters shows only one character without any blending.

b. Self pollination of F1 offsprings

c. Cross pollination of F1 generation with recessive parent

d. Self pollination of F1 offsprings

Answer: a

Explanation: When Mendel crossed pure tall and pure dwarf plants, the F1 generation were all tall, with no intermediate (blended) heights. This observation of distinct, unblended traits led to his concept of discrete hereditary "factors" (genes).

16. Two genes 'A' and 'B' are linked. In a dihybrid cross involving these two genes, the F1 heterozygote is crossed with homozygous recessive parental type (aa bb). What would be the ratio of offspring in the next generation?

a. 1:1:1:1

b. 9:3:3:1

c. 3:1

d. 1:1

Answer: d

Explanation: Because genes A and B are linked, they do not assort independently and are inherited as a single unit (assuming complete linkage). Consequently, a test cross of the heterozygote yields only parental phenotypes in a 1:1 ratio, rather than the 1:1:1:1 ratio expected of unlinked genes.

17. In the F2 generation of a Mendelian dihybrid cross the number of phenotypes and genotypes are:

a. Phenotypes - 4; genotypes 16

b. Phenotypes - 9; genotypes 4

c. Phenotypes - 4; genotypes - 8

d. Phenotypes - 4; genotypes - 9

Answer: d

Explanation: A standard Mendelian dihybrid cross produces a 9:3:3:1 phenotypic ratio (4 distinct observable phenotypes). However, analyzing the genetic combinations reveals there are 9 distinct genotypes that give rise to those 4 phenotypes.  

18. Mother and father of a person with 'O' blood group have 'A' and 'B' blood group, respectively. What would be the genotype of both mother and father?  

a. Mother is homozygous for 'A' blood group and father is heterozygous for 'B'

b. Mother is heterozygous for 'A' blood group and father is homozygous for 'B'

c. Both mother and father are heterozygous for 'A' and 'B' blood group, respectively

d. Both mother and father are homozygous for 'A' and 'B' blood group, respectively

Answer: c

Explanation: The 'O' blood group phenotype requires a homozygous recessive genotype (ii). For the child to inherit an 'i' allele from both parents, the type 'A' mother must be heterozygous (IA i) and the type 'B' father must also be heterozygous (IB i).