Assertion (A):
Genes which code for a pair of contrasting traits are known as alleles.
Reason (R):
Alleles are slightly different forms of the same gene.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: A  [ A ]

Remark: A defines alleles. R explains that alleles are different forms of the same gene. The definition (R) supports the role of alleles (A) in coding for contrasting traits.

Assertion (A):
The Punnett Square is a graphical representation used to calculate the probability of all possible genotypes of offspring in a genetic cross.
Reason (R):
The Punnett Square was developed by British geneticist, Reginald C. Punnett.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: B  [ B ]

Remark: A is True: The Punnett Square is a graphical tool for calculating genotype probability. R is True: It was developed by Reginald C. Punnett. R is a historical fact and does not explain the function described in A.

Assertion (A):
A heterozygous monohybrid plant (Tt) produces two kinds of gametes, T and t, with equal proportion.
Reason (R):
The segregation of alleles is a random process, giving a 50 per cent chance of a gamete containing either allele.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: A  [ A ]

Remark: A is the result of the Law of Segregation for a heterozygote. R explains that the process is random and that 50% probability is the measurable consequence of that randomness.

Assertion (A):
In the F₂ generation of a monohybrid cross, 3/4th of the plants are Tall (phenotype).
Reason (R):
The Tall plants consist of 1/4th homozygous dominant (TT) and 1/2 heterozygous (Tt) genotypes.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: A  [ A ]

Remark: A is the phenotypic ratio observed in F₂. R provides the precise genotypic breakdown (1/4 TT + 1/2 Tt) that sums up to the total Tall phenotype (3/4th) due to dominance.

Assertion (A):
When Mendel crossed a plant with yellow, round seeds (RRYY) and green, wrinkled seeds (rryy), the F₁ generation (RrYy) had yellow and round seeds.
Reason (R):
Yellow colour was dominant over green, and round shape was dominant over wrinkled.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: A  [ A ]

Remark: The F₁ phenotype (A) is explained by the Law of Dominance (R), where the dominant alleles mask the recessive alleles.

Assertion (A):
Mendel’s Law of Independent Assortment holds true for genes located far apart on the same chromosome.
Reason (R):
Distantly located genes, due to recombination, assort independently.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: A  [ A ]

Remark: A describes a condition where the law holds. R explains that for distantly located genes, recombination is frequent enough (approaching 50%) that they effectively assort independently.

Assertion (A):
The behaviour of chromosomes during meiosis parallels the behaviour of genes.
Reason (R):
Chromosomes as well as genes occur in pairs, and the two alleles of a gene pair are located on homologous sites on homologous chromosomes.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: A  [ A ]

Remark: Sutton and Boveri noted the parallel behaviour (A). R provides the physical basis for this parallelism: both occur in pairs, and alleles reside on homologous chromosomes.

Assertion (A):
Thomas Hunt Morgan worked with Drosophila melanogaster to provide experimental verification of the Chromosomal Theory of Inheritance.
Reason (R):
Morgan observed that the genes for yellow body and white eyes did not segregate independently of each other.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: B  [ B ]

Remark: A is True: Morgan verified the chromosomal theory using Drosophila. R is True: He observed that these specific genes showed non-independent segregation (linkage). R is a specific finding from the overall research program (A), but not the reason Morgan chose to undertake the verification work.

Assertion (A):
Morgan coined the term linkage to describe the physical association of genes on a chromosome.
Reason (R):
He coined the term recombination to describe the generation of non-parental gene combinations.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: B  [ B ]

Remark: A is True: Morgan defined linkage as physical association. R is True: Morgan defined recombination as the generation of non-parental gene combinations. Both are true definitions provided by Morgan but are distinct concepts.

Assertion (A):
Grasshopper is an example of the XO type of sex determination.
Reason (R):
In grasshoppers, males have only one X-chromosome besides the autosomes, whereas females have a pair of X-chromosomes.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
• (B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
• (C) Assertion is true but Reason is false
• (D) Assertion is false but Reason is true
Correct Option: A  [ A ]

Remark: A states the mechanism in grasshoppers. R describes the chromosomal composition (male XO, female XX) that defines this type of sex determination.