Who is credited with proposing the Chromosomal Theory of Inheritance?

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

• Gregor Mendel
• T.H. Morgan
• Sutton and Boveri
• Watson and Crick
Correct Option: C  [ Sutton and Boveri ]

Remark: Sutton and Boveri proposed that genes are located on chromosomes that undergo segregation and independent assortment.

The cross mentioned in the text: Tall plant with yellow seeds (TtYy) and a Tall plant with green seed (Ttyy). What proportion of the offspring are expected to be Tall and Green?

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

• 3/16
• 1/4
• 3/8
• 9/16
Correct Option: C  [ 3/8 ]

Remark: This is a dihybrid cross: (Tt x Tt) × (Yy x yy). Probability Tall = 3/4, Green = 1/2 → overall = 3/8.

If the two loci for the cross TtYy × Ttyy were linked, what would be the distribution of phenotypic features in the offspring compared to independent assortment?

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

• The frequency of parental types would decrease.
• The frequency of parental types would increase.
• All offspring would be parental types.
• All offspring would be recombinant types.
Correct Option: B  [ The frequency of parental types would increase. ]

Remark: Linkage increases parental combination frequency and decreases recombinant types.

Which term describes the phenomenon where a single gene influences multiple phenotypic traits?

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

• Polygenic inheritance
• Pleiotropy
• Multiple allelism
• Epistasis
Correct Option: B  [ Pleiotropy ]

Remark: Pleiotropy occurs when one gene affects multiple unrelated characteristics, e.g., phenylketonuria gene.

The allelic interaction where both alleles are expressed equally in the heterozygote, such as in the roan coat color of cattle (RW), is called:

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

• Incomplete dominance
• Co-dominance
• Complete dominance
• Epistasis
Correct Option: B  [ Co-dominance ]

Remark: In co-dominance, both alleles are equally expressed, showing characteristics of both parents.

When two heterozygous parents (Bb) are crossed, the probability of the offspring being heterozygous is:

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

• 1/4
• 1/2
• 3/4
• 1/8
Correct Option: B  [ 1/2 ]

Remark: Cross Bb × Bb gives BB, Bb, Bb, bb — 2 out of 4 (½) are heterozygous.

What is the term for a gene that expresses itself only in the homozygous condition?

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

• Dominant gene
• Recessive gene
• Allele
• Trait
Correct Option: B  [ Recessive gene ]

Remark: A recessive gene expresses only when two identical alleles are present (tt or rr).

In the cross Tt × tt, what is the expected ratio of Tall to Dwarf offspring?

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

• 3:1
• 1:1
• 2:1
• 1:2:1
Correct Option: B  [ 1:1 ]

Remark: A monohybrid test cross Tt × tt produces 1 Tall : 1 Dwarf.

Which of the following is NOT an exception to Mendelian principles?

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

• Co-dominance
• Law of Segregation
• Linkage
• Multiple Allelism
Correct Option: B  [ Law of Segregation ]

Remark: The Law of Segregation is a core Mendelian principle, not an exception.

What is the physical basis for the Law of Independent Assortment?

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

• The separation of sister chromatids during Meiosis II.
• The pairing of homologous chromosomes during Meiosis I.
• The independent arrangement of homologous pairs at the metaphase plate during Meiosis I.
• The formation of the spindle fibers during Mitosis.
Correct Option: C  [ The independent arrangement of homologous pairs at the metaphase plate during Meiosis I. ]

Remark: Independent assortment is physically demonstrated by the random and independent orientation of each pair of homologous chromosomes at Metaphase I of meiosis.