Free Chromosomes MCQs with Answers

1. A human somatic cell contains how many chromosomes?

• A. 23
• B. 44
• C. 46
• D. 92

Explanation: Human body cells are diploid with 46 chromosomes, which is 23 homologous pairs made up of 22 pairs of autosomes and one pair of sex chromosomes. Gametes are haploid and carry 23. The count of 92 would only appear briefly after replication if chromatids were miscounted as separate chromosomes, which they are not.

2. The region of a chromosome where the two sister chromatids are joined and to which spindle fibres attach is the

• A. telomere
• B. centromere
• C. centriole
• D. chromomere

Explanation: The centromere holds sister chromatids together and carries the kinetochore, the protein structure the spindle microtubules attach to during division. Telomeres are the protective caps at the chromosome ends that shorten with each replication. Centrioles are separate cytoplasmic structures that organise the spindle rather than part of the chromosome.

3. In a eukaryotic chromosome, DNA is packaged by winding around proteins called

• A. histones
• B. collagens
• C. tubulins
• D. keratins

Explanation: Histones are small positively charged proteins that bind the negatively charged phosphate backbone of DNA, forming nucleosomes that condense roughly two metres of DNA into a nucleus a few micrometres across. Tubulin builds microtubules, collagen is a structural protein of connective tissue, and keratin is found in hair and nails.

4. A karyotype is

• A. the complete set of genes in a gamete
• B. the sequence of bases in one chromosome
• C. a display of all the chromosomes of a cell arranged in pairs by size and shape
• D. the number of chromatids in a chromosome

Explanation: Chromosomes are photographed at metaphase, when they are most condensed, then cut out and arranged in numbered pairs, which makes an abnormal number or a structural change immediately visible. This is how Down syndrome is confirmed as an extra copy of chromosome 21. It shows chromosome number and shape only, not the base sequence or the individual genes.

5. Of the 23 pairs of chromosomes in a human somatic cell, the number of pairs of autosomes is

• A. 22
• B. 23
• C. 21
• D. 44

Explanation: Twenty two pairs are autosomes, which carry the genes for body characters and are identical in appearance in both sexes, and the remaining pair are the sex chromosomes, XX in a female and XY in a male. The figure 44 is the total number of individual autosomes rather than the number of pairs, which is the usual careless error. A gamete carries 22 autosomes plus one sex chromosome.

6. The powerhouse of the cell is

• A. Nucleus
• B. Mitochondria
• C. Chloroplast
• D. Ribosome

Explanation: Mitochondria are called the powerhouse because they produce ATP through oxidative phosphorylation.

7. What is the function of a centromere?

• A. To protect the ends of chromosomes
• B. To hold sister chromatids together
• C. To carry genetic information
• D. To initiate DNA replication

Explanation: The centromere joins the two sister chromatids and carries the kinetochore, the protein plate that the spindle microtubules attach to during division. Protecting the chromosome ends is the job of the telomeres, which is the closest distractor here. Genetic information is carried along the whole length of the DNA rather than at one point, and replication begins at origins distributed across the chromosome.

8. A mature duplicated chromosome consists of:

• A. Two identical double helical DNA molecules
• B. Two different double helical DNA molecules
• C. A double helical DNA molecule distributed in both chromatids
• D. Histone chains wrapped around DNA core

Explanation: Replication is semi conservative and highly accurate, so the two sister chromatids each hold a complete double helix and the two are identical copies joined at the centromere. They are not different molecules, which is what distinguishes sister chromatids from homologous chromosomes. Note also that DNA wraps around the histones rather than the other way round, which makes the last option backwards.

9. Identify the most appropriate function of chromosomes

• A. Energy production and storage
• B. Protein synthesis and regulation
• C. Storage of genetic information
• D. Lipid metabolism and transport

Explanation: A chromosome is DNA packaged with histones, and its role is to hold the hereditary information and pass it on accurately when the cell divides. Protein synthesis is the tempting option, since genes direct it, but the synthesis itself happens on ribosomes and the chromosome only stores the instructions. Energy production belongs to mitochondria and lipid handling to the smooth endoplasmic reticulum.

10. __________ arranges the DNA into the chromosomes in a eukaryotic cell.

• A. Hormones
• B. Elastin
• C. Histone
• D. Nucleosome

Explanation: Histones are small positively charged proteins that the negatively charged DNA winds around, condensing roughly two metres of DNA into a nucleus a few micrometres across. A nucleosome is the resulting bead of DNA wrapped around eight histones, so it is the product of the packaging rather than the agent doing it, which makes it the deliberate near miss here. Elastin is a structural protein of connective tissue.