Evolution And Speciation ( Populations In Ecosystems, Genetic Diversity And Adaptation ) )

Question 1

Malaria is a disease that destroys red blood cells.
Scientists investigated whether certain red blood cell phenotypes were associated with developing severe or mild malaria. They compared the red blood cell phenotypes of hospital patients suffering from severe malaria
with the red blood cell phenotypes of patients suffering from mild malaria.
The results are shown in the table.

Red blood cell phenotype:

1 ) Sickle Cell trait

2 ) Blood group A

3 ) Blood group O

Ratio of patients with severe malaria : patients with mild malaria:

1 ) 0.48 : 1

2 ) 2.45 : 1

3 ) 0.96 : 1

Explain the advantage of presenting the results as a ratio.

Answer 1

The advantage of presenting the results as a ratio is:

• It allows comparison
• The sample size may vary

Question 2

What do these data show about the effect of red blood cell phenotypes on the chance of developing severe malaria rather than mild malaria?

( Malaria is a disease that destroys red blood cells.
Scientists investigated whether certain red blood cell phenotypes were associated with developing severe or mild malaria. They compared the red blood cell phenotypes of hospital patients suffering from severe malaria
with the red blood cell phenotypes of patients suffering from mild malaria.
The results are shown in the table.

Red blood cell phenotype:

1 ) Sickle Cell trait

2 ) Blood group A

3 ) Blood group O

Ratio of patients with severe malaria : patients with mild malaria:

1 ) 0.48 : 1

2 ) 2.45 : 1

3 ) 0.96 : 1 )

Answer 2

Results show that the effect of red blood cell phenotypes on the chance of developing severe malaria rather than mild malaria is:

• There’s an increased chance of severe malaria with blood group A
• There’s a slightly greater chance of mild malaria with blood group O

Question 3

The allele for normal haemoglobin in red blood cells is Hb^A.
In some parts of Africa where malaria occurs there is a high frequency in the population of the allele Hb^C.
Individuals possessing the Hb^C allele have a lower chance of developing severe malaria.
Severe malaria causes a large number of deaths in Africa.
Explain the high frequency of the Hb^C allele in areas where malaria occurs.

( Malaria is a disease that destroys red blood cells.
Scientists investigated whether certain red blood cell phenotypes were associated with developing severe or mild malaria. They compared the red blood cell phenotypes of hospital patients suffering from severe malaria
with the red blood cell phenotypes of patients suffering from mild malaria.
The results are shown in the table.

Red blood cell phenotype:

1 ) Sickle Cell trait

2 ) Blood group A

3 ) Blood group O

Ratio of patients with severe malaria : patients with mild malaria:

1 ) 0.48 : 1

2 ) 2.45 : 1

3 ) 0.96 : 1 )

Answer 3

High frequency of the Hb^C allele in areas where malaria occurs is due to:

• Individuals with Hb^C allele reproduce
• And pass on the Hb^C allele which increases in frequency
• Hb^AHb^A individuals are less likely to survive

Question 4

Schizophrenia is a mental illness.
Doctors investigated the relative effects of genetic and environmental factors on the development of schizophrenia.
They used sets of identical twins and non-identical twins in their investigation.
At least one twin in each set had developed schizophrenia.

• Identical twins are genetically identical.
• Non-identical twins are not genetically identical.
• The members of each twin pair were raised together.

The table shows the percentage of cases where both twins had developed schizophrenia.

Type of twin:

1 ) Identical

2 ) Non-identical

Percentage of cases where both twins had developed schizophrenia:

1 ) 50

2 ) 15

Explain why both types of twin were used in this investigation.

Answer 4

Both types of twin were used in this investigation because:

• Identical twins show genetic differences between them
• Non-identical twins also show an environmental influence

Question 5

What do these data suggest about the relative effects of genetic and environmental
factors on the development of schizophrenia?

( Schizophrenia is a mental illness.
Doctors investigated the relative effects of genetic and environmental factors on the development of schizophrenia.
They used sets of identical twins and non-identical twins in their investigation.
At least one twin in each set had developed schizophrenia.

• Identical twins are genetically identical.
• Non-identical twins are not genetically identical.
• The members of each twin pair were raised together.

The table shows the percentage of cases where both twins had developed schizophrenia.

Type of twin:

1 ) Identical

2 ) Non-identical

Percentage of cases where both twins had developed schizophrenia:

1 ) 50

2 ) 15 )

Answer 5

The relative effects of genetic and environmental factors on the development of schizophrenia are:

• Genes play a greater role than environmental in the influence of the development of schizophrenia

Question 6

Suggest two factors that the scientists should have taken into account when selecting the twins to be used in this study.

( Schizophrenia is a mental illness.
Doctors investigated the relative effects of genetic and environmental factors on the development of schizophrenia.
They used sets of identical twins and non-identical twins in their investigation.
At least one twin in each set had developed schizophrenia.

• Identical twins are genetically identical.
• Non-identical twins are not genetically identical.
• The members of each twin pair were raised together.

The table shows the percentage of cases where both twins had developed schizophrenia.

Type of twin:

1 ) Identical

2 ) Non-identical

Percentage of cases where both twins had developed schizophrenia:

1 ) 50

2 ) 15 )

Answer 6

Factors that the scientists should have taken into account when selecting the twins to be used in this study are:

• Age
• Sex of non-identical twins