To determine the genotype of an organism showing a dominant phenotype, such as a tall F₂ plant, Mendel crossed it with the recessive parent, a cross he called a _______.

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

• Test cross
• Back cross
• Reciprocal cross
• Monohybrid cross
Correct Option: A  [ Test cross ]

Remark: To determine the genotype of a tall plant at F2, Mendel crossed it with a dwarf plant, which he called a test cross.

Mendel's First Law, the Law of _______, is used to explain the expression of only one of the parental characters in a monohybrid cross in the F₁ generation.

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

• Dominance
• Segregation
• Independent Assortment
• Purity of Gametes
Correct Option: A  [ Dominance ]

Remark: The First Law or Law of Dominance is used to explain the expression of only one of the parental characters in a monohybrid cross in the F1.

The Law of Segregation is based on the fact that the alleles do not show any _______ and that both characters are recovered as such in the F₂ generation.

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

• Blending
• Mutation
• Linkage
• Hybridisation
Correct Option: A  [ Blending ]

Remark: The Law of Segregation is based on the fact that the alleles do not show any blending and that both the characters are recovered as such in the F2 generation.

In the case of incomplete dominance in Snapdragon, the F₂ phenotypic ratio (1 Red : 2 Pink : 1 White) is identical to the _______ ratio (1:2:1).

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

• Genotypic
• Dihybrid
• Phenotypic F1
• Mendelian
Correct Option: A  [ Genotypic ]

Remark: In incomplete dominance, the genotype ratios (1:2:1) were exactly as expected in a Mendelian monohybrid cross, but the phenotype ratios had changed from the 3:1 ratio.

The unmodified (functioning) allele that produces the enzyme required for a substrate transformation is the dominant allele, and the modified allele, which is non-functional or produces no enzyme, is generally the _______ allele.

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

• Recessive
• Codominant
• Lethal
• Neutral
Correct Option: A  [ Recessive ]

Remark: The unmodified (functioning) allele, which represents the original phenotype is the dominant allele and the modified allele is generally the recessive allele.

In human ABO blood grouping, when alleles I^A and I^B are present together, they both express their own types of sugars, a phenomenon called _______.

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

• Co-dominance
• Incomplete Dominance
• Multiple Allelism
• Pleiotropy
Correct Option: A  [ Co-dominance ]

Remark: When IA and IB are present together they both express their own types of sugars, which is because of co-dominance.

The ABO blood grouping system in humans provides a good example of _______ because there are three alleles (I^A, I^B, and i) governing the same character in the population.

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

• Multiple alleles
• Polygenic inheritance
• Incomplete dominance
• Epistasis
Correct Option: A  [ Multiple alleles ]

Remark: The example of ABO blood grouping provides a good example of multiple alleles, where there are more than two, i.e., three alleles, governing the same character.

If starch grain size is considered as the phenotype in pea seeds (controlled by alleles B and b), the heterozygotes (Bb) produce intermediate size grains, indicating _______ dominance.

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

• Incomplete
• Complete
• Co
• Over
Correct Option: A  [ Incomplete ]

Remark: If starch grain size is considered as the phenotype, the alleles show incomplete dominance because the starch grains produced are of intermediate size in Bb seeds.

Mendel's Law of Independent Assortment states that when two pairs of traits are combined in a hybrid, segregation of one pair of characters is _______ of the other pair of characters.

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

• Independent
• Dependent
• Linked
• Associated
Correct Option: A  [ Independent ]

Remark: The Law of Independent Assortment states that segregation of one pair of characters is independent of the other pair of characters.

Mendel's work remained unrecognised until 1900 partly because his approach of using _______ to explain biological phenomena was totally new and unacceptable to many biologists of his time.

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

• Mathematics
• Cytology
• Chemistry
• Microscopy
Correct Option: A  [ Mathematics ]

Remark: Mendel's approach of using mathematics to explain biological phenomena was totally new and unacceptable to many of the biologists of his time.