Cambridge Checkpoint Biology - Grade 8 Practice Questions
Topic 7: Genes and Inheritance
🎮 Section A: Multiple Choice (Choose the correct
answer)
1.
What is the function of a gene?
A) To carry food around the body
B) To control a characteristic or trait
C) To fight against diseases
D) To provide energy for the cell
2.
3.
Which of the following is true about chromosomes?
A) They are made of proteins only
B) They are found outside the nucleus
C) They contain DNA and genes
D) Each human cell contains only one
4.
5.
A boy has brown eyes and his sister has blue eyes. Brown eyes are dominant
over blue eyes. What are the possible genotypes of their parents?
A) BB and BB
B) BB and Bb
C) Bb and Bb
D) bb and bb
6.
7.
What do we call different versions of the same gene?
A) Chromosomes
B) DNA
C) Traits
D) Alleles
8.
9.
Which of these best describes a recessive allele?
A) It always shows in the phenotype
B) It is only expressed when there are two copies
C) It is found only in the mother’s DNA
D) It cannot be passed on to offspring
10.
💪 Section B: Short Answer Questions
1.
Define the following terms:
a) Gene
b) Chromosome
c) Allele
d) Homozygous
2.
3.
A tall plant (T) is crossed with a short plant (t). All offspring are tall.
a) What does this tell you about the allele for tallness?
b) Use a Punnett square to show the cross between two of the tall offspring (Tt
× Tt).
c) What is the ratio of tall to short plants in the second generation?
4.
5.
Explain the difference between inherited and environmental characteristics.
Give one example of each.
6.
🔬 Section C: Challenge Question
1.
In guinea pigs, the allele for black fur (B) is dominant over the allele for white
fur (b). A black guinea pig is crossed with a white one. All the offspring have
black fur.
a) What are the genotypes of the parents?
b) If two of the black offspring are crossed, what percentage of their babies
will be white?
2.
🧪 Section D: More Practical & Challenging Questions
1.
A scientist observes that fruit flies have red or white eyes. The allele for red
eyes (R) is dominant over white eyes (r).
a) What are the possible genotypes of a red-eyed fly?
b) Two red-eyed flies are crossed and they produce some white-eyed
offspring. What are the genotypes of the parents?
2.
3.
A DNA sample is taken from a crime scene. It matches one of three suspects.
a) Why is DNA useful in identifying individuals?
b) What is the risk of using only a small DNA sample?
4.
5.
A couple wants to know if they are both carriers of cystic fibrosis, a recessive
genetic condition.
a) If both parents are carriers (Ff), what is the chance their child will have
cystic fibrosis?
b) Draw a Punnett square to support your answer.
6.
7.
Imagine you're working in a lab, using models of chromosomes to
demonstrate inheritance.
a) How would you use colored pipe cleaners to represent different alleles?
b) What could be a limitation of using models to teach inheritance?
8.
9.
In a rare species of rabbit, fur color is controlled by incomplete dominance.
RR = red fur
WW = white fur
RW = pink fur
Two pink rabbits are crossed.
10.
a) What is the genotypic and phenotypic ratio of their offspring?
b) What’s the key difference between co-dominance and incomplete
dominance?
11.
✅ Answer Key
Section A:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Section B:
6. a) A gene is a section of DNA that controls a characteristic.
b) A chromosome is a thread-like structure made of DNA found in the nucleus.
c) Alleles are different forms of the same gene.
d) Homozygous means having two identical alleles for a gene.
1.
a) Tallness is dominant.
b) Punnett square:
2.
T t
--------
T | TT | Tt |
t | Tt | tt |
c) Ratio = 3 tall : 1 short
1.
Inherited: controlled by genes (e.g., hair color).
Environmental: influenced by surroundings (e.g., accent).
2.
Section C:
9. a) Bb (black) × bb (white)
b) 25% white from Bb × Bb cross
Section D:
10. a) RR or Rr
b) Both must be Rr to produce rr (white)
1.
a) DNA is unique to each person
b) Small samples might give errors or contamination
2.
3.
a) 25% chance of affected child
b) Punnett square:
4.
F f
--------
F | FF | Ff |
f | Ff | ff |
ff = affected (1 out of 4)
13. a) Use different colors for dominant/recessive alleles
b) Models can be too simple, not show molecular details
1.
a) Genotypes = 1 RR : 2 RW : 1 WW; Phenotypes = 1 red : 2 pink : 1 white
b) In co-dominance both traits show equally (e.g., AB blood), in incomplete
dominance the traits blend (e.g., pink)
2.
