Chapter 3: Chromosomal Basis of Inheritance — Online MCQ Test
BOTANY · CLASS 12th · Tamil Nadu State Board
Practice Chapter 3: Chromosomal Basis of Inheritance with a free chapter-wise online MCQ test.
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....
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Chapter 3: Chromosomal Basis of Inheritance — Important Questions & Answers
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.
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.
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.
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.
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%.
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%.