A Tt plant, which is heterozygous for genes controlling one character (height), is known as a _______.

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

• Monohybrid
• Dihybrid
• Test cross
• Homozygote
Correct Option: A  [ Monohybrid ]

Remark: Since the Tt plant is heterozygous for genes controlling one character (height), it is a monohybrid.

The graphical representation developed by Reginald C. Punnett to calculate the probability of all possible genotypes of offspring in a genetic cross is called the _______.

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

• Punnett Square
• Pedigree Chart
• Binomial Expression
• Karyotype
Correct Option: A  [ Punnett Square ]

Remark: The production of gametes and offspring can be understood from a diagram called Punnett Square, developed by Reginald C. Punnett.

In a typical monohybrid cross, the phenotypic ratio observed in the F2 generation is _______.

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

• 3:1
• 1:2:1
• 9:3:3:1
• 1:1
Correct Option: A  [ 3:1 ]

Remark: In the F2 generation, the phenotypic ratio is 3/4th tall : 1/4th tt, i.e., a 3:1 ratio.

The genotypic ratio of TT: Tt: tt in the F2 generation of a monohybrid cross is _______.

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

• 1:2:1
• 3:1
• 1:1:1:1
• 9:3:3:1
Correct Option: A  [ 1:2:1 ]

Remark: The 1/4 : 1/2 : 1/4 ratio of TT: Tt: tt represents a genotypic ratio of 1:2:1.

A cross used to determine the genotype of an organism showing a dominant phenotype by crossing it with the recessive parent is called a _______.

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

• Test cross
• Back cross
• Dihybrid 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 Second Law is known as the Law of _______, which states that alleles do not show any blending and segregate during gamete formation.

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

• Segregation
• Dominance
• Independent Assortment
• Inheritance
Correct Option: A  [ Segregation ]

Remark: Mendel's Second Law is the Law of Segregation, based on the fact that alleles do not show blending and segregate such that a gamete receives only one factor.

The inheritance of flower colour in the dog flower (Antirrhinum sp.), where a cross between red (RR) and white (rr) produces pink (Rr) F₁ progeny, is a classic example of _______.

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

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

Remark: In the dog flower, the F1 (pink) had a phenotype in between the two parents, demonstrating incomplete dominance.

When the F₁ generation resembles both parents, such as in human ABO blood grouping where I^A and I^B are expressed simultaneously, the phenomenon is called _______.

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

• Co-dominance
• Incomplete dominance
• Multiple allelism
• Linkage
Correct Option: A  [ Co-dominance ]

Remark: In co-dominance, the F1 generation resembles both parents; when $I^A$ and $I^B$ are present together they both express their own types of sugars.

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

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

• Multiple alleles
• Polygenic inheritance
• Incomplete dominance
• Pleiotropy
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 (three) alleles governing the same character.

In a dihybrid cross, the phenotypic ratio observed in the F2 generation, such as round, yellow to wrinkled, green, is _______.

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

• 9:3:3:1
• 3:1
• 1:2:1
• 1:1:1:1
Correct Option: A  [ 9:3:3:1 ]

Remark: In the dihybrid cross, the phenotypes appeared in the ratio 9:3:3:1.