1. Which of the following processes is responsible for the formation of genetic recombination in meiosis?
a) Independent assortment
b) Crossing over
c) Cytokinesis
d) DNA replication
Answer: b) Crossing over
Explanation: Crossing over occurs during meiosis, specifically in prophase I, and results in the exchange of genetic material between homologous chromosomes, leading to genetic recombination.
2. Which of the following is a type of chromosomal aberration that results in the loss of a part of a chromosome?
a) Duplication
b) Inversion
c) Deletion
d) Translocation
Answer: c) Deletion
Explanation: Deletion is a chromosomal aberration in which a segment of a chromosome is lost. This can lead to the loss of important genes and has various effects on the organism.
3. In cytogenetics, the term “polyploidy” refers to:
a) A condition where there is an abnormal number of chromosomes in the cell
b) The presence of more than two complete sets of chromosomes in an organism
c) The loss of a single chromosome from the chromosomal set
d) The rearrangement of genes on a chromosome
Answer: b) The presence of more than two complete sets of chromosomes in an organism
Explanation: Polyploidy refers to the condition in which an organism has more than two complete sets of chromosomes, often seen in plants and some animals, and can be induced artificially for crop improvement.
4. Which of the following statements about Down syndrome is true?
a) It is caused by a duplication of chromosome 21
b) It results from an extra copy of chromosome 13
c) It is caused by trisomy of chromosome 21
d) It is caused by a translocation between chromosome 21 and chromosome 13
Answer: c) It is caused by trisomy of chromosome 21
Explanation: Down syndrome is caused by trisomy 21, which means the individual has three copies of chromosome 21 instead of the usual two, leading to developmental and physical abnormalities.
5. Which type of chromosomal mutation is characterized by the reversal of the orientation of a chromosome segment?
a) Duplication
b) Deletion
c) Inversion
d) Translocation
Answer: c) Inversion
Explanation: Inversion is a chromosomal mutation where a chromosome segment is reversed, and the genes within this region are flipped, which can affect gene expression or cause genetic disorders.
6. In human genetics, a karyotype analysis involves:
a) Studying the sequence of DNA base pairs
b) Counting and identifying chromosomes in a cell
c) Analyzing the pattern of gene expression
d) Determining the nucleotide composition of a gene
Answer: b) Counting and identifying chromosomes in a cell
Explanation: Karyotype analysis involves the examination of chromosomes in a cell, usually during metaphase, to determine the number, size, and shape of chromosomes, which helps in diagnosing chromosomal disorders.
7. In cytogenetics, a “centric fusion” is best described as:
a) The fusion of two non-homologous chromosomes resulting in a metacentric chromosome
b) The separation of chromatids during mitosis
c) The loss of a chromosome during cell division
d) The fusion of two identical chromatids to form a diploid structure
Answer: a) The fusion of two non-homologous chromosomes resulting in a metacentric chromosome
Explanation: Centric fusion is the joining of the centromeres of two non-homologous chromosomes, which results in the formation of a metacentric chromosome, leading to structural chromosomal abnormalities.
8. What is the major consequence of a Robertsonian translocation?
a) Loss of genetic material
b) Formation of a ring chromosome
c) Fusion of two acrocentric chromosomes
d) Inversion of a chromosomal segment
Answer: c) Fusion of two acrocentric chromosomes
Explanation: Robertsonian translocation is a type of chromosomal rearrangement in which the long arms of two acrocentric chromosomes fuse, often resulting in a reduction of the chromosome number without the loss of genetic material.
9. Which of the following is NOT a characteristic of aneuploidy?
a) It involves the gain or loss of individual chromosomes
b) It can lead to conditions like Down syndrome or Turner syndrome
c) It always results in a normal phenotype
d) It can occur due to errors in meiosis
Answer: c) It always results in a normal phenotype
Explanation: Aneuploidy involves an abnormal number of chromosomes (either extra or missing) and typically leads to phenotypic abnormalities, such as Down syndrome (trisomy 21) or Turner syndrome (monosomy X).
10. In the context of cytogenetics, “C-banding” is a technique used to:
a) Identify specific genes on chromosomes
b) Distinguish heterochromatin from euchromatin
c) Visualize translocation events between chromosomes
d) Measure the DNA content in cells
Answer: b) Distinguish heterochromatin from euchromatin
Explanation: C-banding is a cytogenetic technique that stains the heterochromatin regions of chromosomes, typically at the centromere, helping in the identification of chromosomal regions rich in repetitive DNA.
11. Which of the following chromosomal abnormalities is associated with infertility in humans?
a) Trisomy 21
b) Klinefelter syndrome
c) Turner syndrome
d) Both b and c
Answer: d) Both b and c
Explanation: Both Klinefelter syndrome (47, XXY) and Turner syndrome (45, X) are associated with infertility. Klinefelter syndrome leads to male infertility, while Turner syndrome causes female infertility due to the absence of one X chromosome.
12. In cytogenetics, what is “gene dosage” and how can it be affected by chromosomal mutations?
a) The number of alleles present for a particular gene
b) The amount of genetic material in the genome
c) The number of copies of a gene that are present, which can be altered in cases of deletions or duplications
d) The distribution of genes across chromosomes
Answer: c) The number of copies of a gene that are present, which can be altered in cases of deletions or duplications
Explanation: Gene dosage refers to the number of copies of a particular gene in a cell. It can be altered in cases of chromosomal mutations such as deletions or duplications, leading to either a deficiency or an excess of gene expression.
13. Which of the following genetic disorders is caused by a chromosomal inversion?
a) Chronic myelogenous leukemia
b) Down syndrome
c) Hemophilia
d) None of the above
Answer: a) Chronic myelogenous leukemia
Explanation: Chronic myelogenous leukemia (CML) is caused by a specific chromosomal inversion known as the Philadelphia chromosome, which involves the translocation of genetic material between chromosomes 9 and 22.
14. The “Barr body” is typically found in:
a) Males only
b) Females only
c) Both males and females
d) Both males and females, but only in individuals with Turner syndrome
Answer: b) Females only
Explanation: A Barr body is an inactivated X chromosome, typically found in females, as they have two X chromosomes, and one is randomly inactivated in each cell to balance gene dosage between males and females.
15. Which of the following can cause a “deletion” in a chromosome?
a) Unequal crossing over
b) Transposition
c) Robertsonian translocation
d) All of the above
Answer: a) Unequal crossing over
Explanation: Unequal crossing over during meiosis can lead to chromosomal deletions or duplications when homologous chromosomes do not align properly, resulting in the loss of genetic material.