Chromosomal Alterations Questions and Answers

Q: In Drosophila, the phenomenon of translocation was first discovered by:

Translocation was first discovered in Drosophila by Bridges (1923). Calvin Bridges studied chromosome rearrangements in the fruit fly.Morgan worked on linkage and sex-linked inheritance, Mendel on the laws of inheritance in peas, and Darwin on evolution, so they are not credited with translocation.Bridges worked with Morgan's group on Drosophila and described chromosome rearrangements including translocation in the early 1920s. He is also known for the discovery of non-disjunction.

Q: A change in chromosome number, whether by adding or subtracting a whole part or whole set of a haploid complement, is termed:

The key's answer is Polyploidy.A change in the number of chromosomes is a numerical aberration. Adding or losing a whole set of chromosomes is euploidy, of which polyploidy (three or more sets) is the main form, while adding or losing single chromosomes is aneuploidy. Of the options offered, polyploidy is the only change in chromosome number.Translocation, inversion and duplication are structural aberrations: they rearrange, reverse or repeat segments of chromosomes without changing their number.

Q: Which among the following phenomena interfers with the balance theory of sex determination in Drosophila ?

The phenomenon is non-disjunction.Bridges' genic balance theory says sex in Drosophila depends on the balance between X chromosomes and sets of autosomes. Non-disjunction, the failure of chromosomes to separate at meiosis, upsets that balance by producing gametes with extra or missing X chromosomes. The resulting flies, such as XXY females, XO males, and the intersexes and metafemales from triploid lines, change the X:A ratio and the sex that follows; studying them is how Bridges worked the theory out.Linkage and crossing over rearrange alleles but do not change chromosome numbers, and sex in Drosophila is genetic, not environmental.

In Drosophila, the phenomenon of translocation was first discovered by:

A.Darwin
B.Morgan
C.Mendel
D.Bridges

Exam Year(s)

DSSSB PGT - 2023,

Answer: D

Translocation was first discovered in Drosophila by Bridges (1923). Calvin Bridges studied chromosome rearrangements in the fruit fly.

Morgan worked on linkage and sex-linked inheritance, Mendel on the laws of inheritance in peas, and Darwin on evolution, so they are not credited with translocation.

Bridges worked with Morgan's group on Drosophila and described chromosome rearrangements including translocation in the early 1920s. He is also known for the discovery of non-disjunction.

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In which condition is one pair of chromosomes missing from the somatic chromosome complement?

A.Nullisomy
B.Tetrasomy
C.Monosomy
D.Trisomy

Exam Year(s)

DSSSB PGT - 2023,

Answer: A

Nullisomy is the condition in which a pair of chromosomes is missing from the somatic complement, written 2n - 2. The organism lacks both members of one pair.

Monosomy (2n - 1) lacks one chromosome only, trisomy (2n + 1) has one extra, and tetrasomy (2n + 2) has an extra pair.

The term for a chromosome number 2n - 2 is nullisomic. Nullisomics are often not viable in diploids but are found in polyploids such as wheat, where other chromosomes can make up for the missing pair.

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A change in chromosome number, whether by adding or subtracting a whole part or whole set of a haploid complement, is termed:

A.Translocation
B.Inversion
C.Polyploidy
D.Duplication

Exam Year(s)

RSMSSB Livestock Assistant - 2025, RSMSSB - 2025,

Answer: C

The key's answer is Polyploidy.

A change in the number of chromosomes is a numerical aberration. Adding or losing a whole set of chromosomes is euploidy, of which polyploidy (three or more sets) is the main form, while adding or losing single chromosomes is aneuploidy. Of the options offered, polyploidy is the only change in chromosome number.

Translocation, inversion and duplication are structural aberrations: they rearrange, reverse or repeat segments of chromosomes without changing their number.

Discuss in Forum

Which among the following phenomena interfers with the balance theory of sex determination in Drosophila ?

A.Linkage
B.Non-disjunction
C.Crossing over
D.Environmental

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: B

The phenomenon is non-disjunction.

Bridges' genic balance theory says sex in Drosophila depends on the balance between X chromosomes and sets of autosomes. Non-disjunction, the failure of chromosomes to separate at meiosis, upsets that balance by producing gametes with extra or missing X chromosomes. The resulting flies, such as XXY females, XO males, and the intersexes and metafemales from triploid lines, change the X:A ratio and the sex that follows; studying them is how Bridges worked the theory out.

Linkage and crossing over rearrange alleles but do not change chromosome numbers, and sex in Drosophila is genetic, not environmental.

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