Genetics and Evolution MCQ Questions for CUET UG

Gel electrophoresis is a technique used to separate DNA fragments based on their size. The correct sequence of steps is:

Step 1: Moving of DNA fragments towards the anode (C)
DNA fragments carry a negative charge due to their phosphate backbone.
When an electric field is applied, they migrate through the agarose gel towards the positively charged anode.
Smaller fragments move faster and travel farther than larger ones.
Step 2: Staining with ethidium bromide (B)
After electrophoresis, the gel is stained with ethidium bromide (EtBr).
Ethidium bromide intercalates between DNA base pairs, making the DNA visible under UV light.
Step 3: Exposure to UV light (A)
The stained gel is exposed to ultraviolet (UV) light.
DNA bands fluoresce and become visible, allowing the separated fragments to be identified.
Step 4: Elution (D)
The desired DNA fragment is cut from the gel and extracted.
This process of recovering DNA from the gel is called elution.

Human skin colour is an example of polygenic (quantitative) inheritance, controlled by three pairs of genes:

A/a
B/b
C/c

Each dominant allele (A, B, C) contributes one unit of pigment, while each recessive allele (a, b, c) contributes no pigment.

The amount of melanin produced depends on the total number of dominant alleles.

Transcription is the process by which the genetic information present in one strand of DNA (the template strand) is copied into an RNA molecule by the enzyme RNA polymerase.

It is the first step of gene expression, producing messenger RNA (mRNA), transfer RNA (tRNA), or ribosomal RNA (rRNA), depending on the gene.

Aneuploidy is a chromosomal abnormality in which an individual has one or more extra or missing chromosomes due to nondisjunction during meiosis.

Among the given disorders:
(A) Haemophilia
A sex-linked recessive genetic disorder caused by mutation in genes responsible for blood clotting factors.
It is a single-gene disorder, not due to aneuploidy.
(B) Down's Syndrome
Caused by Trisomy 21 (an extra copy of chromosome 21).
It is a classic example of aneuploidy.
(C) Thalassemia
An autosomal recessive single-gene disorder affecting haemoglobin synthesis.
It is not caused by a change in chromosome number.
(D) Turner's Syndrome
Caused by monosomy X (45, X).
Individuals have only one X chromosome instead of two.
It is an example of aneuploidy.