Principles of Inheritance & Variation - 2 - Free MCQ Practice Test

Statement I: The bridge between one generation and the next is sperm and ovum.

• This is correct. Sperm and ovum are the gametes that combine during fertilization to form a zygote, which then develops into a new individual, thereby bridging generations.

Statement II: Both sperm and ovum contribute equally to heredity.

• This is generally correct, but with a slight clarification. While both sperm and ovum contribute genetic material (DNA), they do so in equal amounts (each contributing one set of chromosomes), meaning the genetic contribution is equal in terms of number of chromosomes. However, the ovum provides the majority of the cytoplasm and organelles, while the sperm provides the genetic material. So, strictly speaking, they contribute equally in terms of the genetic information, but not necessarily in all aspects of heredity.

Statement iii : Somatic diploid cells possess two sets of chromosomes, one set inherited from each parent, and two alleles (Mendelian factors) for each gene, one on each homologous chromosome.

• Somatic diploid cells: These are cells with two complete sets of chromosomes (diploid), one from each parent.
• Two sets of chromosomes: This emphasizes that somatic cells have pairs of chromosomes (in humans, 23 pairs).
• Two alleles for each gene: This clarifies that each gene has two alleles, one on each of the homologous chromosomes.

This sex linked recessive disease, which shows its transmission from unaffected carrier female to some of the male progeny has been widely studied. In this disease, a single protein that is a part of the cascade of proteins involved in the clotting of blood is affected. Due to this, in an affected individual a simple cut will result in non-stop bleeding. The heterozygous female (carrier) for haemophilia may transmit the disease to sons.The possibility of a female becoming a haemophilic is extremely rare because mother of such a female has to be at least carrier and the father should be haemophilic (unviable in the later stage of life). If Mother is normal and father is haemophilic then daughter will be carrier not haemophilic.

Hence, the correct option is D.

NCERT Reference: Topic “Haemophilia” of chapter  "Principles of Inheritance and Variation" of NCERT.

Topic in NCERT: Haemophilia

Line in NCERT: "The possibility of a female becoming a haemophilic is extremely rare because mother of such a female has to be at least carrier and the father should be haemophilic."

• The father of a colour blind female must be colour blind.
• The mother has to be at least a carrier. This is possible if the maternal grandfather was colour blind [remember criss-cross].

Hence, the correct option is B.

NCERT Reference: Topic- Colour Blindness of chapter "Principles of Inheritance and Variation" of NCERT.

• Yellow pod colour of the pea plant is a recessive trait.
• Mendel studied seven contrasting traits in pea (Pisum sativum), which are as follows:

Hence, the correct option is B.

• Both tall and dwarf plants produce gametes by mitosis.
• Plants use meiosis only to produce spores that develop into multicellular haploid gametophytes which produce gametes by mitosis.

Therefore, gamete formation in both tall and dwarf plants is by mitosis.

Hence, the correct option is A.
Note: This question is based on basic understanding of inheritance of genes.

• Gene is a segment of DNA and new alleles arise by mutation - a sudden inheritable change in DNA. Mutations can alter single nucleotides or entire chromosomes.
• The ultimate source of genetic variation is random mutation i.e. changes in nucleotide sequences of DNA. They may involve only a single base pair or many as in chromosomal mutations.
• Change in the allele frequency and introduction of new alleles are the basis of genetic variation occurring in any population.

Fig: Showing Mutation 

Hence, the correct option is C.
NCERT Reference: Topic- MUTATION” of chapter  "Principles of Inheritance and Variation" of NCERT.

In the scenario where a true-breeding red-flowered (RR) plant is crossed with a true-breeding white-flowered (rr) plant in the dog flower species, the resulting F1 offspring displays a pink flower color. This outcome is a classic example of incomplete dominance, where neither of the parental traits dominates completely, leading to an intermediate phenotype in the offspring. This phenomenon is crucial in understanding genetic inheritance patterns beyond simple dominant and recessive relationships.

In the scenario of co-dominance where both I^A and I^B alleles are present, they express their own types of sugars simultaneously. This occurrence is due to the unique nature of co-dominance, where neither allele suppresses the other, resulting in the expression of both sugar types. This leads to red blood cells displaying both A and B types of sugars, showcasing a co-dominant inheritance pattern.

The Law of Segregation clarifies that alleles segregate independently during gamete formation, ensuring that each gamete receives only one of the two factors or alleles from a parent. This segregation process underlies the inheritance of traits and explains why both parental traits are not always visible in the F1 generation. Heterozygous parents, which carry two different alleles for a trait, produce gametes with equal proportions of each allele, contributing to genetic diversity in offspring.

Thalassemia follows an autosomal recessive inheritance pattern, meaning that two copies of the mutated gene are necessary for the disease to manifest.