CIE iGCSE Co-Ordinated Science B16.1 Chromosomes and genes Exam Style Questions Paper 1
Question
Which row is correct for the inheritance of sex in humans?
▶️Answer/Explanation
Answer: A
Explanation: In humans, females have two X chromosomes (XX), and males have one X and one Y chromosome (XY). This determines the inheritance of sex.
Question
Cystic fibrosis is an inherited condition caused by a recessive allele. A man and woman have a child who has cystic fibrosis. Neither parent has the condition. What is the probability of their next child also having cystic fibrosis?
A. 0%
B. 25%
C. 50%
D. 75%
▶️Answer/Explanation
Answer: B
Explanation: Since both parents are carriers (heterozygous) of the recessive allele, there is a 25% chance that their next child will inherit two recessive alleles and thus have cystic fibrosis.
Question
In a species of flowering plant, the allele for red flowers is dominant to the allele for white flowers. A plant breeder crossed a homozygous white-flowered plant with a heterozygous red-flowered plant. What is the expected phenotypic ratio of the next generation of plants?
A) 1 white : 1 red
B) 3 red : 1 white
C) 3 white : 1 red
D) all the plants will be red
▶️Answer/Explanation
Answer: A) 1 white : 1 red
Explanation: The homozygous white-flowered plant has the genotype rr, and the heterozygous red-flowered plant has the genotype Rr. The cross between them (rr x Rr) will produce offspring with genotypes Rr and rr in a 1:1 ratio. Since R (red) is dominant over r (white), the phenotypic ratio will be 1 red : 1 white.
Question
Which statement is correct?
A An allele is a version of a gene.
B DNA is only found in gametes.
C A gene is a length of DNA that codes for fats.
D Cells of human males contain two X chromosomes.
▶️Answer/Explanation
Ans :A
Question
Which diagram correctly shows sex inheritance in humans?
▶️Answer/Explanation
Ans: C
Question
Which sex chromosomes are found in a healthy male human?
(A) XO
(B) XX
(C) XY
(D) YY
▶️Answer/Explanation
Ans : C
Question
In terms of the alleles present, which word describes the genetic make-up of an organism?
A dominant
B genotype
C phenotype
D recessive
▶️Answer/Explanation
Ans : B
Question
The diagram shows eggs and sperm containing sex chromosomes.
Which row gives the correct combination of sex chromosomes for a male and female offspring?
▶️Answer/Explanation
Ans : B
Question
Which combination of sex chromosomes are present in the body cells of a human male?
(A) XX
(B) XY
(C) Y only
(D) YY
▶️Answer/Explanation
Ans: B
Question
Which term is used to describe an individual with two of the same allele for a characteristic?
A. genotype
B. heterozygous
C. homozygous
D. phenotype
▶️Answer/Explanation
Answer: C. homozygous
Explanation: Homozygous refers to an individual having two identical alleles for a particular gene. For example, if an individual has two alleles for tallness (TT), they are homozygous for that trait.
Question
In humans, which combination of sex chromosomes from the ovum and sperm would result in a female?
▶️Answer/Explanation
Answer: A. X from ovum, X from sperm
Explanation: In humans, females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). Therefore, a female is produced when an X chromosome from the ovum combines with an X chromosome from the sperm.
Question
In cats, the allele for short hair is dominant to the allele for long hair. Two long-haired cats are bred together. What hair length will the offspring have?
A. all long-haired
B. all mid-length hair
C. all short-haired
D. 50% long and 50% short-haired
▶️Answer/Explanation
Answer: A. all long-haired
Explanation: Since long hair is a recessive trait, both parent cats must be homozygous recessive (ll). When two homozygous recessive individuals are bred, all offspring will also be homozygous recessive (ll), resulting in all long-haired offspring.
Question
Which statement about human gametes is correct?
A. Only 50% of egg cells contain an X chromosome.
B. Only 50% of sperm cells contain a Y chromosome.
C. 100% of egg cells contain a Y chromosome.
D. 100% of sperm cells contain an X chromosome.
▶️Answer/Explanation
Answer: B. Only 50% of sperm cells contain a Y chromosome.
Explanation: In humans, egg cells always contain an X chromosome, while sperm cells can contain either an X or a Y chromosome. Therefore, only 50% of sperm cells contain a Y chromosome.
Question
Which sex chromosomes need to be present in a sperm cell to produce a male zygote?
A. X only
B. Y only
C. XX
D. XY
▶️Answer/Explanation
Answer: B
Explanation: A sperm cell carrying a Y chromosome will result in a male zygote (XY) when it fertilizes an egg (which always carries an X chromosome).