SSC CGL 2025 Tier-I · 14 September 2025, Shift 1 · General Awareness · Question 14 of 100

We transcribed this text from the pictures on a candidate's response sheet for this shift; the answer is the key SSC colour-marked on that sheet. Solution last reviewed 11 September 2026.

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SSC does not publish CGL question papers or a public answer key. From 2025 the candidate response sheet prints every question and option as a picture, so the text here is transcribed from those pictures for this shift and checked against them independently; where the layout carries meaning, the picture is shown as well. Each answer is the key SSC colour-marked on that sheet. SSC released a tentative key for challenge and later its final one, both only to candidates behind a login, and the sheet does not say which of the two it carries. The solutions are written by UnlockIAS.

The term “pleiotropy” refers to:

(a)One gene affects multiple traits
(b)Multiple genes affect one trait
(c)Gene mutation in one allele
(d)Gene duplication

Answer

Why

Correct — A. NCERT's Class XII Biology says a single gene can show multiple phenotypic expression, and calls such a gene a pleiotropic gene: one gene, several traits.

Its example is phenylketonuria. A mutation in the one gene coding for the enzyme phenylalanine hydroxylase shows up as intellectual disability and reduced hair and skin pigmentation. One gene, many effects: option (a).

Why the others are wrong

(b)
Multiple genes affect one trait — That is polygenic inheritance, the reverse relationship. NCERT's examples are human height and skin colour, traits controlled by three or more genes whose allele effects add up.
(c)
Gene mutation in one allele — A change in one allele is a mutation, an event in the DNA. Pleiotropy is about reach: how many traits one gene affects, whether or not that gene is mutated.
(d)
Gene duplication — Gene duplication is the gain of an extra copy of a DNA segment, which NCERT lists under mutation with deletion and insertion. It changes gene number, not how many traits one gene touches.

Concept

Genes and traits need not match one to one, and this question sets the two mismatches side by side.

Pleiotropy is one gene, several traits. In most cases, NCERT says, the gene acts on metabolic pathways that feed different phenotypes.

Polygenic inheritance is several genes, one trait. Height and skin colour vary along a gradient because each allele adds a small effect, and the environment adds its own.

Key facts

A pleiotropic gene is a single gene with multiple phenotypic expressions (NCERT Class XII Biology, Chapter 4).
Phenylketonuria, caused by a mutation in the gene for phenylalanine hydroxylase, is NCERT's example of pleiotropy.
Polygenic traits such as human height and skin colour are controlled by three or more genes with additive allele effects.
A point mutation is a change in a single base pair of DNA, as in sickle-cell anaemia.

Study next

Polygenic inheritance and additive allele effects in human skin colourPoint mutations, frame-shift mutations and sickle-cell anaemiaMendelian disorders such as phenylketonuria, haemophilia and thalassemia

Common traps

Reversing the two terms: pleiotropy is one gene to many traits, polygenic inheritance is many genes to one trait.
Picking the mutation option because NCERT's pleiotropy example, phenylketonuria, starts with a single-gene mutation.

Here a genetics term is tested by its definition, with its mirror image, polygenic inheritance, as the main distractor.

Related PYQs

No directly related past PYQ was found.

Topic: Scientific Research — all 178 SSC CGL questions on it, every solved shift.