Question 1Multiple choice · 1 markA* challenge
In a molecule of DNA, 22% of the bases are adenine (A).
What percentage of the bases are guanine (G)?
- A 22%
- B 26%
- C 28%
- D 78%
Show answer
Answer: C
Free Chromosomes, genes & proteins questions for IGCSE Biology (0610), part of Inheritance & variation. Each question has the answer and the marking points an examiner would look for.
Generate a full Chromosomes, Genes & Proteins worksheet →All Inheritance & variation questionsIn a molecule of DNA, 22% of the bases are adenine (A).
What percentage of the bases are guanine (G)?
Answer: C
A haploid nucleus contains
Answer: C
Genes are found on chromosomes in the nucleus.
Define a gene.
Define an allele.
Describe how the sequence of bases in a gene controls the protein made.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | length of DNA coding for a protein a length of DNA that codes for a protein B1 | 1 |
| (b) | alternative form of a gene an alternative form of a gene B1 | 1 |
| (c) | triplets code amino acids; mRNA; ribosome the base sequence determines the amino acid sequence B1 mRNA copies the gene and goes to a ribosome B1 amino acids are joined in that order B1 | 3 |
A karyotype shows the chromosomes of a cell.
State the number of pairs of chromosomes in a human body cell.
Explain the meaning of diploid.
State the sex chromosomes of a human male.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 23 23 pairs B1 | 1 |
| (b) | two sets of chromosomes a nucleus containing two sets of chromosomes (pairs) B1 | 1 |
| (c) | XY XY B1 | 1 |
This question is about DNA and protein synthesis.
Describe the structure of a DNA molecule.
Write the sequence of bases on the strand complementary to CGTAAC.
State how the sequence of bases in a gene determines the protein made.
Describe how a protein is made at a ribosome, starting from the gene in the nucleus.
A mutation changes one base in a gene. Explain how this could affect the protein.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | two strands; double helix; bases pair A–T, C–G two strands coiled into a double helix B1 each strand has a sequence of bases B1 bases pair A with T and C with G (complementary) B1 | 3 |
| (b) | GCATTG GCATTG B1 | 1 |
| (c) | base sequence codes for sequence of amino acids the sequence of bases determines the sequence of amino acids B1 which determines the shape and function of the protein B1 | 2 |
| (d) | mRNA copy of gene made in nucleus; moves to ribosome; ribosome reads bases; amino acids joined in correct order the gene is copied into mRNA in the nucleus B1 mRNA passes out of the nucleus to a ribosome B1 the ribosome reads the base sequence (in triplets) B1 amino acids are brought and joined in the order coded B1 | 4 |
| (e) | different amino acid; protein shape changes, may not function may code for a different amino acid B1 changing the shape of the protein so it may not function (e.g. active site) B1 | 2 |
Human body cells contain 46 chromosomes.
State the number of chromosomes in a human sperm cell.
Explain what is meant by a haploid nucleus.
Explain how sex is inherited in humans.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 23 23 B1 | 1 |
| (b) | one set of chromosomes a nucleus containing one set of chromosomes (unpaired) B1 | 1 |
| (c) | XX female, XY male; 50 % chance females are XX and males XY B1 sperm carry X or Y, so there is a 50 % chance of each sex B1 | 2 |
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