Chapter Exam

Chapter 3: Chromosomal Basis of Inheritance — Online MCQ Test

Q: In which stage of prophase I of meiosis does crossing over actually occur?

Answer: C. Pachytene — During the pachytene stage of prophase I, homologous chromosomes form bivalents and crossing over (exchange of genetic material) occurs between non-sister chromatids.

Q: Who coined the term 'linkage' to describe the physical association of genes on a chromosome?

Answer: A. T.H. Morgan — Thomas Hunt Morgan coined the term 'linkage' in 1910 during his cytogenetic work on Drosophila melanogaster.

Q: If the recombination frequency between two genes A and B is 15%, between B and C is 8%, and between A and C is 7%, what is the sequence of these genes on the chromosome?

Answer: B. A - C - B — Since A and B have the largest distance (15 map units), they must be at the ends. The sum of A-C (7) and C-B (8) equals 15, meaning gene C lies between A and B.

Q: A chromosome segment has the gene sequence ABC•DEFG (where • represents the centromere). After a chromosomal aberration, the sequence becomes ABC•DFEG. Identify the type of aberration.

Answer: A. Paracentric inversion — The segment EFG inverted to FEG. Since this inverted segment does not include the centromere (which is located to the left of D), it is a paracentric inversion.

Q: In a three-point test cross involving three linked genes x, y, and z, the recombinant frequencies are: x-y = 10%, y-z = 26%, and x-z = 34%. If the coefficient of coincidence is 0.4, what is the observed frequency of double crossovers?

Answer: B. 1.04% — Expected double crossovers = 0.10 * 0.26 = 0.026 (or 2.6%). Since Coefficient of Coincidence = (Observed Double Crossovers) / (Expected Double Crossovers), Observed = 0.4 * 2.6% = 1.04%.

BOTANY · CLASS 12th · Tamil Nadu State Board

Practice Chapter 3: Chromosomal Basis of Inheritance with a free chapter-wise online MCQ test for Tamil Nadu State Board CLASS 12th BOTANY. This chapter covers: Focusing on cytogenetics this chapter covers linkage crossing over chromosome mapping and gene mapping techniques. Students explore sex determination mechanisms numerical and struc.... AI-generated questions from basic to board-exam level, with instant results and explanations.

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Chapter 3: Chromosomal Basis of Inheritance — Important Questions & Answers (FAQ)

Frequently asked questions from Tamil Nadu State Board CLASS 12th BOTANY — Chapter 3: Chromosomal Basis of Inheritance, with answers and explanations. These are sample questions; the exam has its own separate question set.

In which stage of prophase I of meiosis does crossing over actually occur?

A. Leptotene
B. Zygotene
C. Pachytene ✓
D. Diplotene

Answer: C. Pachytene
During the pachytene stage of prophase I, homologous chromosomes form bivalents and crossing over (exchange of genetic material) occurs between non-sister chromatids.

Who coined the term 'linkage' to describe the physical association of genes on a chromosome?

A. T.H. Morgan ✓
B. Bateson and Punnett
C. Hugo de Vries
D. Gregor Mendel

Answer: A. T.H. Morgan
Thomas Hunt Morgan coined the term 'linkage' in 1910 during his cytogenetic work on Drosophila melanogaster.

If the recombination frequency between two genes A and B is 15%, between B and C is 8%, and between A and C is 7%, what is the sequence of these genes on the chromosome?

A. A - B - C
B. A - C - B ✓
C. C - A - B
D. B - A - C

Answer: B. A - C - B
Since A and B have the largest distance (15 map units), they must be at the ends. The sum of A-C (7) and C-B (8) equals 15, meaning gene C lies between A and B.

A chromosome segment has the gene sequence ABC•DEFG (where • represents the centromere). After a chromosomal aberration, the sequence becomes ABC•DFEG. Identify the type of aberration.

A. Paracentric inversion ✓
B. Pericentric inversion
C. Intercalary deletion
D. Reciprocal translocation

Answer: A. Paracentric inversion
The segment EFG inverted to FEG. Since this inverted segment does not include the centromere (which is located to the left of D), it is a paracentric inversion.

In a three-point test cross involving three linked genes x, y, and z, the recombinant frequencies are: x-y = 10%, y-z = 26%, and x-z = 34%. If the coefficient of coincidence is 0.4, what is the observed frequency of double crossovers?

A. 2.6%
B. 1.04% ✓
C. 3.4%
D. 1.36%

Answer: B. 1.04%
Expected double crossovers = 0.10 * 0.26 = 0.026 (or 2.6%). Since Coefficient of Coincidence = (Observed Double Crossovers) / (Expected Double Crossovers), Observed = 0.4 * 2.6% = 1.04%.

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