Inheritance (Cambridge O Level Biology)

Exam Questions

1 hour23 questions
1a
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1 mark

Fig. 1 shows a white sweet pea flower and a red sweet pea flower.

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Fig. 1

These colours in sweet pea are controlled by a single gene with two alleles.

Define the term allele.

1b
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1 mark

A homozygous sweet pea with white flowers was crossed with a homozygous sweet pea with red flowers. All of the offspring had red flowers.

State which allele of this gene is dominant.

1c
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3 marks

Two heterozygous sweet pea plants with red flowers were crossed as shown below.

58E2iMlq_image

(i)

Draw a Punnet square to show the genotypes that are produced in this cross.

[2]

(ii)

State the phenotypic ratio produced in this cross.

[1]

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2a
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4 marks

Fig. 1 shows a goat with white fur.

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Fig. 1

Fur colour is inherited in goats.

  • The allele for white fur is represented by A.
  • The allele for black fur is represented by a.
  • Each goat is identified by the numbers 1 to 8 in Fig. 2.

Fig. 2 shows a diagram of the inheritance of fur colour in a herd of goats.

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Fig. 2

Use Fig. 2 to answer these questions.

(i)

State how many goats have white fur.

[1]

(ii)

State the phenotype of goat 5.

[1]

(iii)

Draw circles around two terms that can be used to describe the genotype of goat 6.

black                          dominant                          heterozygous

homozygous                            recessive                                white

[2]

2b
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1 mark

State the name of the type of variation shown by fur colour in these goats.

2c
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3 marks

A farmer identified two goats to breed together.

  • The genotype of the male goat is Aa.
  • The genotype of the female goat is Aa.

Complete the genetic diagram and the phenotypic ratio for this cross.

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2d
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3 marks

Describe the process a farmer could use to breed a herd of white goats.

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1a
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3 marks

A rabbit that was homozygous for black fur was crossed with a rabbit that was homozygous for brown fur.

All of their offspring had black fur.

This is shown in Fig. 1.

cie-igcse-2018-s3-may-p3-q6b-bunnies

Fig. 1

(i)

Define the term homozygous.

[1]

(ii)

State the dominant allele for the rabbits' fur colour and give a reason for your answer.

[2]
1b
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1 mark

The F1 offspring all have the same phenotype as the male parent but their genotype is not the same as the male parent.

State how the phenotype of an organism is different to its genotype.

[1]
1c
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4 marks

A rabbit with brown fur is mated with one of the F1 rabbits with black fur.

Complete the genetic diagram to show the possible fur colours that could occur from this mating.

cie-igcse-2018-s3-may-p3-q6d-inheritance-q-layout

[4]

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2a
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3 marks

Fig. 1 shows the sequence of events that occur in sexual reproduction.

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Fig. 1

(i)

State the name of cell T in Fig. 1.

[1]

(ii)

State the name of the process that takes place at S to form cell T in Fig. 1.

[1]

(iii)

State where in the human body process S takes place.

[1]

2b
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5 marks

Some humans have the ability to roll their tongues and some cannot roll their tongues.

This characteristic is controlled by genes.

Fig. 2 shows two boys: boy A cannot roll his tongue and boy B can roll his tongue.

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Fig. 2

The allele for tongue rolling (T) is dominant to the allele for non-tongue rolling (t).

Fig. 3 shows a family tree for this characteristic. Individual 1 and his partner are both heterozygous for tongue rolling.

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Fig. 3

(i)
Complete Table 1 by inserting the genotypes of the numbered individuals in Fig. 3.

Table 1

Individual Genotype
1  
3  
4  

[3]

(ii)

Individual 2 in Fig. 3 is heterozygous for tongue rolling. He marries a woman who cannot roll her tongue.

State all of the possible genotypes of their children and predict the ratio of phenotypes for their children.

[2]

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36 marks

One parent of a child has blood group B and the other parent has blood group A. The child has blood group O.

The parents decide to have another child.

(i)
Complete the genetic diagram in Fig. 3.1 to show the possible blood groups for the second child of these parents.

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(ii)


State the probability that the second child of these parents:

has the same sex as the first child ............................................................
has the same blood group as the first child ...............................................
 [2]

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45 marks

Some people inherit a condition which prevents the production of the dark pigment melanin in their choroid and skin cells. The gene involved has two alleles, A (dominant)  and a (recessive).

Only people with two recessive alleles have this condition.

Two people, each with a heterozygous genotype, have children together.

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(i)
Complete the genetic diagram to show the possible genotypes and phenotypes of the children.

[4]

(ii)
State the probability of these two people having a child who does not produce melanin.
[1]

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1
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4 marks

Fig. 1 shows a cat with an inherited condition that means the cat has extra toes.

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Fig. 1

The allele that causes this condition is dominant to the allele for the normal condition.

Fig. 2 shows the inheritance of this condition in a family of cats.

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Fig. 2

Complete Table 1 by stating the genotypes of the numbered individuals.

Use B for the dominant allele and b for the recessive allele.

Table 1

number of individual in Fig. 2 genotype of individual
1  
2  
4  
14  

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2a
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3 marks

The four o’clock plant, Mirabilis jalapa, can have flowers of three different colours as shown in Fig. 1.

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Fig .1

A student crossed some red-flowered plants with some yellow-flowered plants (cross 1).

She collected the seeds and grew them. All of the plants that grew from these seeds had orange flowers.

Complete the genetic diagram to explain the result of cross 1.

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2b
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3 marks

The student then carried out three further crosses as shown in Table 1.

Table 1

  genotypes of offspring
cross 2 offspring of cross 1 × offspring of cross 1  
cross 3 offspring of cross 1 × red-flowered plant  
cross 4 offspring of cross 1 × yellow-flowered plant  

Complete the table by writing in the genotypes of the offspring of crosses 2, 3 and 4, using the same symbols as in the genetic diagram in (a).

2c
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3 marks

Flower colour in M. jalapa is not an example of the inheritance of dominant and recessive alleles.

Explain how the results of the crosses show that these alleles for flower colour are not dominant or recessive. 

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