CIE iGCSE Co-Ordinated Science B16.3 Monohybrid inheritance Exam Style Questions Paper 1
Question
Purple flower colour is dominant to white flower colour.
Which parents must be crossed to make sure all the offspring have white flowers?
A homozygous dominant × heterozygous
B homozygous dominant × homozygous dominant
C homozygous recessive × heterozygous
D homozygous recessive × homozygous recessive
▶️Answer/Explanation
Ans : D
Question
What is the correct term for an allele that is always expressed in the phenotype if it is present?
(A) dominant
(B) heterozygous
(C) homozygous
(D) recessive
▶Answer/Explanation
Ans : A
Question
Which statement describes a heterozygous genotype?
(A) not pure breeding with two different alleles
(B) not pure breeding with two identical alleles
(C) pure breeding with two different alleles
(D) pure breeding with two identical alleles
▶️Answer/Explanation
Ans: A
Question
Albinism is a genetic condition which results in an absence of pigment in the skin, hair and eyes.
If two black mice produce an albino offspring, which Punnett square shows the correct cross?
▶️Answer/Explanation
Ans: B
Question
Two parents with genotypes of BB and Bb were crossed. Which genotypes and ratios would be expected in the offspring?
A. 1 BB: 1 Bb
B. 1 Bb: 1 bb
C. 3 BB: 1 Bb
D. 3 Bb: 1 BB
▶️Answer/Explanation
Answer: A. 1 BB: 1 Bb
Explanation: When crossing BB (homozygous dominant) with Bb (heterozygous), the possible genotypes of the offspring are BB and Bb. The Punnett square shows a 1:1 ratio of BB to Bb offspring.
Question
In some plants, the red flower allele is dominant to the yellow flower allele. Two heterozygous red-flowered plants are crossed. Which statement about the offspring produced is correct?
A. 25% of plants will have red flowers, 75% will have yellow flowers.
B. 50% of plants will have red flowers, 50% will have yellow flowers.
C. 75% of plants will have red flowers, 25% will have yellow flowers.
D. 100% of plants will have red flowers.
▶️Answer/Explanation
Answer: C. 75% of plants will have red flowers, 25% will have yellow flowers.
Explanation: When two heterozygous red-flowered plants (Rr) are crossed, the offspring will have a genotypic ratio of 1 RR : 2 Rr : 1 rr. Since red (R) is dominant over yellow (r), 75% of the offspring will have red flowers, and 25% will have yellow flowers.
Question
A pure-breeding mouse with black fur was bred with a pure-breeding mouse with white fur. All the offspring had black fur. What are the genotypes of the two parent mice?
A Bb × bb
B Bb × Bb
C BB × bb
D BB × BB
▶️Answer/Explanation
Answer: C
Explanation: Since all offspring have black fur, the black fur allele (B) must be dominant. The parents are pure-breeding, so one must be homozygous dominant (BB) and the other homozygous recessive (bb).