Zoology MCQs
Topic Notes: Zoology
MCQs and preparation resources for competitive exams, covering important concepts, past papers, and detailed explanations.
Plato
- Biography: Ancient Greek philosopher (427–347 BCE), student of Socrates and teacher of Aristotle, founder of the Academy in Athens.
- Important Ideas:
- Theory of Forms
- Philosopher-King
- Ideal State
1
What is the specific term for a genetic mutation where a single nucleotide base is replaced by a different base?
Answer:
substitution
A substitution mutation occurs when one nitrogenous base in a DNA sequence is replaced by another. This can lead to silent, missense, or nonsense mutations depending on the resulting codon change. Unlike insertions or deletions, substitutions do not typically cause a frame shift unless they affect splice sites.
2
Which chromosomal mutation occurs when a segment of a chromosome breaks off, rotates 180 degrees, and reattaches in the reverse orientation?
Answer:
inversion
An inversion is a type of chromosomal rearrangement where a segment of the chromosome is reversed end-to-end. This change in gene order can affect gene expression and may lead to evolutionary divergence or genetic disorders depending on the location of the breakpoints.
3
What is the result of adding a single chromosome to the normal diploid number (2N+1)?
Answer:
trisomy
Trisomy is a specific type of aneuploidy where an individual has three copies of a particular chromosome instead of the usual two. This condition (2N+1) often results from nondisjunction during meiosis, where chromosomes fail to separate correctly, leading to gametes with an extra chromosome.
4
Aneuploidy, a condition characterized by an abnormal number of chromosomes, typically arises from errors during which biological process?
Answer:
meiosis
Aneuploidy is primarily caused by nondisjunction, which is the failure of homologous chromosomes or sister chromatids to separate correctly during meiosis. This results in gametes with an incorrect number of chromosomes. When these gametes fuse during fertilization, the resulting zygote will have an abnormal chromosome count, leading to various genetic disorders.
5
What is the standard diploid number of chromosomes found in human somatic cells?
Answer:
46
The normal human karyotype consists of 46 chromosomes, arranged in 23 pairs. This includes 22 pairs of autosomes and one pair of sex chromosomes (XX in females and XY in males), which carry the genetic information necessary for human development and function.
6
What is the term for the genetic condition where multiple copies of chromosomes are present?
Answer:
duplication
Duplication refers to a type of mutation where a portion of a chromosome or a whole chromosome is replicated, resulting in extra genetic material. While the term 'polyploidy' is often used for whole sets of chromosomes, 'duplication' is the standard term for the presence of extra copies of genetic segments.
7
What is the term for the highly condensed, transcriptionally inactive region of a chromosome?
Answer:
heterochromatin
Heterochromatin is a tightly packed form of DNA or condensed chromatin that is generally inaccessible to the machinery required for gene expression. Because it remains condensed throughout the cell cycle, it is considered transcriptionally inactive compared to the more loosely packed euchromatin.
8
What is the specific term used to describe the chromosomal aberration where a segment of a chromosome is lost?
Answer:
deletion
Deletion is a type of mutation involving the loss of a chromosomal segment. This loss can result in significant genetic imbalances, as the organism loses specific genes located within the deleted region. It is distinct from addition (duplication), translocation (movement of segments between non-homologous chromosomes), and inversion (reversal of a segment's orientation).
9
What term refers to a permanent alteration in the DNA sequence or chromosomal structure of an organism?
Answer:
mutation
A mutation is a change in the nucleotide sequence of the genome of an organism. Mutations can result from errors during DNA replication or exposure to mutagens. They can involve single base pairs, entire genes, or larger chromosomal segments, and are the primary source of genetic variation.
10
What is the specific term for a genetic mutation that results from the addition of an extra nucleotide base pair into the DNA sequence?
Answer:
insertion
An insertion is a type of mutation where one or more nucleotide base pairs are added into a DNA sequence. While insertions can lead to frameshift mutations if they occur in a coding region and are not a multiple of three, the specific act of adding the base is defined as an insertion. This can significantly alter the resulting protein structure and function.