2.4 Inheritance

State the meaning of the terms:

Genotype

(1)

Phenotype

(2)

Cystic fibrosis is a disease caused by a recessive allele. 

Use the diagram to explain the evidence for this. 

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.

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

Which breakthrough did Meselson and Stahl achieve? 

Explain why DNA replication is described as semiconservative.

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.

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

(2)

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

(3)

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

Give two reasons why the scientists used bacteria.

(2)

Explain why the scientists used nitrogen isotopes.

(2)

There are different types of gene mutation.

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

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.

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

An insertion mutation alters Gene 1.

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

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.

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.

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

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

(1)

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			2=

Complete the missing values in the table.

(3)

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

Assess whether the null hypothesis should be accepted or rejected.

(3)