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📝 Chromosomes and genes (7 MCQs)

📖 From Campbell Biology • 1. Evolution and the theme of Biology and Scientific Inquiry • 7 questions available

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What is Chromosomes and genes?

Definition:
Chromosomes are organized structures containing DNA and associated proteins, while genes are specific DNA sequences located on chromosomes that provide information for functional products such as proteins or functional RNA. Together, chromosomes organize and preserve hereditary information within cells.

Working:
DNA is packaged into chromosomes, and genes occupy particular positions called loci. Genes can influence traits by directing the production or regulation of biological molecules.

Example:
A chromosome may contain thousands of genes, with one gene providing instructions for a protein involved in pigment production.

Reason:
Understanding chromosomes and genes explains how genetic information is organized and how inherited DNA sequences can influence characteristics of organisms.

Easy

Medium

Hard

📝 All Chromosomes and genes MCQs

Q1. A student observes that chromosomes contain DNA and that genes are specific regions of this DNA. Which conclusion best explains the relationship between chromosomes, DNA, and genes?

A.Genes are made of proteins that attach to chromosomes

B.Chromosomes are structures containing DNA, while genes are functional DNA sequences that influence traits ✅

C.Each chromosome contains only one gene that determines one trait

D.DNA exists only in genes and is absent from the remaining chromosome

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: Chromosomes are organized structures composed primarily of DNA and associated proteins. Genes are specific DNA sequences located on chromosomes that provide information influencing biological functions or traits. Therefore, genes are parts of chromosomes rather than separate structures.

Q2. Two cells from the same organism contain the same chromosome number, but one cell produces a muscle-specific protein while another produces a neuron-specific protein. Which explanation best accounts for this difference?

A.The cells must contain completely different chromosomes

B.Different cells can use different sets of genes even when their DNA is largely the same ✅

C.Only muscle cells contain genes, whereas neurons contain chromosomes without genes

D.The chromosome number determines exactly which proteins every cell must produce

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: Most cells in a multicellular organism contain essentially the same genetic information, but they can activate different genes. Differential gene expression allows cells to produce different proteins and develop specialized structures and functions despite sharing chromosomes.

Q3. A researcher studies a gene associated with pigment production. A mutation changes its DNA sequence, and the organism develops altered pigmentation. Which chain of reasoning most appropriately connects the mutation to the observed trait?

A.The mutation changes a DNA sequence, which can alter gene function and consequently affect a biological characteristic ✅

B.The mutation increases chromosome number, which automatically changes pigmentation

C.The mutation converts the chromosome directly into a protein responsible for pigmentation

D.The mutation affects only DNA replication and therefore cannot influence traits

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: A gene contains DNA information that can influence the production or regulation of biological molecules. A mutation can alter that information, potentially changing gene function and downstream cellular processes that contribute to an observable trait.

Q4. A student claims: "If two individuals have the same chromosome number, they must have identical genes and therefore identical traits." Which criticism most effectively identifies the error?

A.Chromosome number alone does not determine the exact DNA sequences, gene variants, or gene activity present in individuals ✅

B.Individuals with the same chromosome number cannot have any genetic similarities

C.Traits are determined entirely by chromosome number and never by DNA sequence

D.Genes are found only outside chromosomes, so chromosome number is irrelevant

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: Having the same chromosome number does not mean that individuals have identical DNA sequences. Differences can occur in gene variants and regulatory regions, and environmental influences and gene expression can also contribute to differences in traits.

Q5. A laboratory records the relative expression of a particular gene in four cell samples. The values are: Sample A = 20, Sample B = 45, Sample C = 70, Sample D = 30. If higher expression means greater activity of that gene, which sample should show the greatest effect of the gene's product?

A.Sample A

B.Sample B

C.Sample C ✅

D.Sample D

💡 Difficulty: medium | ✅ Correct: C

📖 Explanation: The numerical values represent relative gene expression, so the largest value indicates the greatest activity of the gene under the stated assumption. Sample C has an expression value of 70, higher than all three other samples.

Q6. A scientist compares two individuals. Individual X has two copies of a chromosome, while Individual Y also has two copies, but their DNA sequences at a particular gene differ. Both individuals show different versions of the associated trait. What is the best interpretation?

A.The different traits can result from different versions of the same gene located on corresponding chromosomes ✅

B.The difference proves that Individual Y has an extra chromosome

C.The two individuals must have completely different chromosome structures

D.Having two chromosome copies prevents any variation in genes

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: Corresponding chromosomes can carry different versions of the same gene. These alternative DNA sequences can influence gene products or their regulation differently, potentially producing variation in traits even when chromosome number remains unchanged.

Q7. A model proposes that a trait depends on two genes located on the same chromosome. A mutation disrupts one gene, but the second gene continues functioning normally. Which prediction is most scientifically reasonable?

A.Both genes must stop functioning because they occupy the same chromosome

B.Only the disrupted gene is necessarily affected directly, while the second gene may continue functioning unless the mutation also influences it ✅

C.The chromosome will immediately disappear from the cell

D.The mutation will automatically double the number of copies of both genes

💡 Difficulty: hard | ✅ Correct: B

📖 Explanation: Genes located on the same chromosome are physically associated, but a mutation in one gene does not automatically eliminate or disable every neighboring gene. The second gene can remain functional unless the mutation affects its sequence, regulation, or chromosome structure.

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