Inheritance Practice Questions

Question 1

3 marks

In rabbits, coat colour is controlled by a single gene. The allele for black fur, $B$ , is dominant to the allele for brown fur, $b$ .

(a)

A rabbit has the genotype $Bb$ .

This rabbit is described as

A homozygous dominant
B heterozygous
C homozygous recessive
D a gamete

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(b)

State the phenotype of a rabbit with the genotype $bb$ .

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(c)

State what is meant by the term allele.

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Question 2

4 marks

In humans, sex is determined by the sex chromosomes. A female has two X chromosomes and a male has one X and one Y chromosome.

The Punnett square below shows the gametes produced by a mother and a father.

	X	X
X
Y

(a)

Complete the Punnett square to show the genotypes of the possible offspring.

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(b)

State the probability that a child of these parents will be male.

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(c)

Explain why it is the father, and not the mother, who determines the sex of a child.

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Question 3

3 marks

Variation in a characteristic may be caused by genes, by the environment, or by both.

Complete the table by placing one tick (✓) in each row to show the cause of variation in each characteristic.

Characteristic	Genes only	Environment only	Both genes and environment
ABO blood group
A scar caused by a cut
Body mass of a person

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Question 4

3 marks

A population of wild poppies growing on a roadside shows extensive genetic variation.

(a)

Which of these describes a mutation?

A the fusion of two gametes
B a change in the sequence of bases in DNA
C a section of DNA that codes for a protein
D the combination of alleles in an organism

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(b)

State the effect that most mutations have on the phenotype of an organism.

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(c)

State how new alleles arise in the poppy population.

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Question 0

7 marks

Gregor Mendel investigated inheritance in pea plants in the 1860s.

He crossed pure-breeding tall pea plants with pure-breeding dwarf pea plants. All of the offspring in the first generation were tall.

He then allowed the first generation plants to self-pollinate. The second generation contained 812 tall plants and 268 dwarf plants.

(a)

Explain what the results of the first cross show about the allele for dwarf stems.

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(b)

Use a Punnett square to explain the numbers of tall and dwarf plants in the second generation.

Use $T$ for the tall allele and $t$ for the dwarf allele.

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(c)

Mendel's ideas were not accepted by other scientists during his lifetime.

Give two reasons for this.

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Question 0

5 marks

In tomato plants, fruit colour is controlled by a single gene. The allele for red fruit, $R$ , is dominant to the allele for yellow fruit, $r$ .

(a)

A grower crosses a heterozygous red-fruited plant with a yellow-fruited plant.

Complete the Punnett square to show this cross.

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(b)

State the expected ratio of red-fruited to yellow-fruited offspring from this cross.

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(c)

The grower then crosses two heterozygous red-fruited plants and grows 240 seedlings from the seeds produced.

Calculate the number of these seedlings expected to produce yellow fruit.

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Question 0

5 marks

Cystic fibrosis is a genetic disorder caused by an allele of a single gene.

The family pedigree below shows the inheritance of cystic fibrosis in one family.

(a)

Explain how the pedigree shows that cystic fibrosis is caused by a recessive allele.

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(b)

Give the genotypes of individuals 1 and 2.

Use $F$ for the dominant allele and $f$ for the recessive allele.

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(c)

Individuals 1 and 2 are expecting another child.

Calculate the probability that this child will be a girl with cystic fibrosis.

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Question 0

4 marks

The ABO blood group system in humans is controlled by a gene with three alleles: $I^A$ , $I^B$ and $I^O$ .

The alleles $I^A$ and $I^B$ are codominant. The allele $I^O$ is recessive.

(a)

Explain, using blood group AB as an example, what is meant by codominant alleles.

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(b)

A man with the genotype $I^AI^O$ has children with a woman with the genotype $I^BI^O$ .

Use a genetic diagram to show the blood groups their children could have.

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Question 0

4 marks

Most human characteristics, such as height, are controlled by many genes as well as being affected by the environment.

Identical twins have exactly the same alleles.

(a)

Give one example of a human characteristic that is controlled by a single gene.

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(b)

A pair of identical twins were separated at birth and brought up in different countries. As adults, one twin is 8 cm taller than the other.

Explain how this difference in height has arisen.

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Question 0

5 marks

In pea plants, flower colour is controlled by a single gene. The allele for purple flowers, $P$ , is dominant to the allele for white flowers, $p$ .

(a)

Explain the difference between a gene and an allele.

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(b)

Name the cell that is formed when two gametes fuse at fertilisation.

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(c)

Two heterozygous purple-flowered pea plants were crossed. Seeds from this cross were collected and planted.

One of the seeds grew into a plant with purple flowers and another grew into a plant with white flowers.

Explain why these two plants have different flower colours.

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Question 0

6 marks

Red-green colour blindness is a sex-linked condition caused by a recessive allele carried on the X chromosome.

The dominant allele is shown as $X^B$ and the recessive allele as $X^b$ .

A woman who is a carrier of colour blindness has children with a man who is not colour blind.

(a)

Complete a Punnett square to show the possible genotypes of the children of this couple.

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(b)

Calculate the probability that a son of this couple will be colour blind.

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(c)

Explain why red-green colour blindness is much more common in males than in females.

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Question 0

6 marks

The Human Genome Project finished sequencing the first human genome in 2003.

Some companies now offer a service in which a person pays to have their own genome sequenced. The results are given to the person and to their doctor.

Evaluate the use of this service by members of the public.

In your answer you should refer to the outcomes of the Human Genome Project and to the effects on the individual.

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Question 0

6 marks

Huntington's disease is a genetic disorder of the nervous system. It is caused by an allele of a single gene.

The family pedigree below shows the inheritance of Huntington's disease in one family.

(a)

Explain how the pedigree shows that Huntington's disease is caused by a dominant allele.

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(b)

Deduce the genotype of individual 3.

Use $H$ for the dominant allele and $h$ for the recessive allele. Explain your answer.

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(c)

Individual 6 has children with a man who does not have Huntington's disease.

Calculate the probability that one of their children will have Huntington's disease. You may use a genetic diagram in your answer.

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Question 0

5 marks

The ABO blood group gene has three alleles: $I^A$ , $I^B$ and $I^O$ .

A woman with blood group O and a man with blood group AB have three children.

(a)

Explain what is meant by the statement that the ABO blood group gene has multiple alleles.

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(b)

Use a genetic diagram to determine the blood groups that the children of this couple could have, and the probability of each.

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(c)

A fourth child born to the woman has blood group O.

Explain what this shows about this child.

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Key Concepts in Biology

Cells & Control

Genetics

Natural Selection & Genetic Modification

Health, Disease & the Development of Medicines

Plant Structures & their Functions

Animal Coordination, Control & Homeostasis

Exchange & Transport in Animals

Ecosystems & Material Cycles

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