Inheritance (Edexcel A (SNAB) AS Biology)

Exam Questions

52 mins5 questions
1a
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2 marks

A scientist replicated DNA in a test tube. To do this, they mixed an enzyme with identical DNA fragments into a solution containing free DNA nucleotides.

Name the enzymes used in this DNA replication and state their function.

1b
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1 mark

Explain the role of the free DNA nucleotides.

1c
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2 marks

State two features of DNA and explain how each one is important in semi-conservative replication. 

1d
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4 marks

The diagram below shows the replication fork during semiconservative replication. The arrows show the directions in which each new DNA strand is being produced.

Use your knowledge of enzymes and DNA structure to explain why the arrows point in opposite directions.


enzyme

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2a
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3 marks

State the meaning of the terms:

(i)

Genotype

(1)

(ii)

Phenotype

(2)

2b
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2 marks

Cystic fibrosis is a disease caused by a recessive allele. 

pedigree-chart-example-1

Use the diagram to explain the evidence for this. 

2c
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4 marks

Couple 5 and 6 decide to have another child. 

Determine the probability that this child will be a female with cystic fibrosis.

Use a genetic diagram in your answer.

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3a
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1 mark

Two scientists, named Matthew Meselson and Franklin Stahl, made a huge scientific breakthrough during the 1950s.

Which breakthrough did Meselson and Stahl achieve? 

  A The double helix structure of DNA
  B Semi-conservative replication of DNA
  C First genome sequenced
  D DNA profiling 

3b
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2 marks

Explain why DNA replication is described as semiconservative.

3c
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5 marks

As part of their experiments the scientists, named in part (a), grew bacteria for several generations on a medium containing 'Heavy Nitrogen' 15N. They then transferred these bacteria to a medium containing 14N and analysed their DNA over three stages using density gradient centrifugation. 

Their results are shown below.

generations-0-1-2

tubes

(i)

Complete the diagrams of the test tubes showing the DNA from the bacteria at the different generations of growth. 

(2)

(ii)

Explain how the results of their experiments showed that the theory of conservative replication was incorrect

(3)

3d
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4 marks

The scientists used E.coli and a growth media containing the different isotopes of nitrogen. 

(i)

Give two reasons why the scientists used bacteria.

(2)

(ii)

Explain why the scientists used nitrogen isotopes.

(2)

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4a
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1 mark

There are different types of gene mutation.

Select which of A - D that does not describe a type of gene mutation.

  A Insertion of a base changes the codon and can lead to a new amino acid being incorporated
  B Duplication will result in a new base sequence through addition of a nucleotide
  C Substitution mutations can be silent, missense or nonsense
  D Deletion of a base changes the codon and can lead to a new amino acid being incorporated

4b
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3 marks

Fruit flies have three different colour eyes: red, sepia or white. 

The diagram below shows a pathway of how different eye colours may be produced by the eye cells.

pigments

Suggestion why a substitution mutation in gene 1 will still lead to red eye colours in the fruit flies.

4c
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6 marks

An insertion mutation alters Gene 1.

Explain how the mutation could result in fruit flies with only white eyes.

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5a
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2 marks

Wolves show variation in eye colour. One of the genes for eye colour in wolves has two alleles; the allele for yellow eyes (Y) is dominant over the allele for green eyes (y). 

Two wolves bred together in captivity over a number of years. Both had yellow eyes and their offspring showed the following phenotypes:

  • 24 with yellow eyes
  • 12 with green eyes

Deduce, with a reason, the parental genotypes of the wolves.

5b
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3 marks

Predict the expected ratio of offspring from a cross between the two parent wolves described in part (a).

You may use a genetic diagram as part of your answer.

5c
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7 marks

A chi-squared test can be carried out to analyse the results of the wolf cross. 

(i)

Select the most appropriate null hypothesis for the test from A-D.

(1)

  A There is no significant difference between the expected and observed eye colours of the wolf offspring
  B There is a significant difference between the expected and observed eye colours of the wolf offspring
  C The difference between the expected and observed eye colours has a genetic basis and is not due to chance alone
  D The offspring of the breeding wolf pair show the expected results for eye colour

(ii)

The table below shows the observed values for each eye colour phenotype in the wolf offspring.

Eye colour Observed eye colour (O) Expected eye colour (E) O-E (O-E)2 (O-E)2/E
Yellow 25        
Green 17        
Total     chi2=  

Complete the missing values in the table.

(3)

(iii)

The table below shows the critical values of chi-squared at different degrees of freedom.

Degrees of freedom P = 0.05
1 3.841
2 5.991 
3 7.815
4 9.488
5 11.070

Assess whether the null hypothesis should be accepted or rejected.

(3)

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