Past Paper Questions

Question 1

importance of collecting a sample at random

Answer 1

to avoid bias can only apply a stat test to randomly collected data

Question 2

In birds, males are XX and females are XY. Use this information to explain why recessive, sex-linked characteristics are more common in female birds than in male birds.

Answer 2

Recessive) allele is always expressed in females / females have one (recessive) allele / males need two recessive alleles/ males need to be homozygous recessive / males could have dominant and recessive alleles/be heterozygous/carriers;

Question 3

Explain the advantage of presenting the results as a ratio.

Answer 3

1. Allows (valid) comparison; 2. Number/sample size may vary;

Question 4

The allele for normal haemoglobin in red blood cells is HbA. In some parts of Africa where malaria occurs there is a high frequency in the population of the allele HbC. Individuals possessing the HbC 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 HbC allele in areas where malaria occurs.

Answer 4

1. Individuals with the HbC (allele) reproduce; 2. Pass on HbC (allele) which increases in frequency; 3. HbA HbA individuals less likely to survive/reproduce / frequency of HbA (allele) decreases;

Question 5

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

Answer 5

Increased chance of (severe malaria) with blood group A / decreased chance of (severe malaria) with sickle cell;

One mark for one of the following:

almost equal chance with blood group O /slightly greater chance of mild malaria with O /slightly lower chance of severe malaria with O /2.5 x/2.48 x/more than twice the chance of severe with blood group A
/(almost) 50%/half the chance of severe malaria with sickle cell
/twice the chance of mild malaria with sickle cell;

Question 6

Explain one piece of evidence from Figure 3 which shows that the allele for rapid feather production is recessive.

Answer 6

1, (2) and 5;

1 must possess/pass on the recessive allele / 1 must be a carrier / heterozygous / if slow (feather production) is recessive all offspring of (1 and 2) would be slow (feather production) / if rapid (feather production) was dominant 1 would have rapid (feather production);

Question 7

Explain one piece of evidence from the diagram which proves that the allele for Tay-Sachs disease is recessive.

Explain one piece of evidence from the diagram which proves that the allele for Tay-Sachs disease is not on the X chromosome.

Answer 7

3 and 4 and 9/11/affected offspring;

Both 3 and 4 are carriers/heterozygous;

OR

If dominant at least one of 3 and 4 would be affected;

11 is affected, 3 is not;

3/father of 11 does not have a recessive allele on his X chromosome/ Xt;

Question 8

Explain what is meant by the term phenotype.

Answer 8

Expression / appearance / characteristic due to genetic constitution/genotype/allele(s);

(Expression / appearance / characteristic) due to environment;

Question 9

The actual percentage of heterozygotes is likely to be lower in future generations than the answer to part (c)(i). Explain why.

Answer 9

Affected individuals (usually) do not reproduce/die during childhood/do not pass on allele/genetic screening;

Question 10

During the last 700 000 years there have been long periods when the water level was much lower and Lake Malawi split up into many smaller lakes. Explain how speciation of the cichlids may have occurred following the formation of separate, smaller lakes.

Answer 10

solation of two populations;
variation already present due to mutations;
different environmental conditions / selection pressures; selection of different features and hence different alleles; different frequency of alleles;
separate gene pools / no interbreeding;

Question 11

Give evidence from the diagram which sugegsts that MD is

sex linked

caused by a recessive allelle

Answer 11

(a) (i) Only seen in males / not in females;
(ii) Unaffected parents/mother → child with M.D./ (1 ×)2 → 5 / (3 ×) 4 → 11 / 8 (× 9) → 13;

Question 12

(i) Explain one piece of evidence from the diagram which shows that the allele for Rhesus positive is dominant.

Answer 12

3 and 4/two Rhesus positives produce Rhesus negative

child/children/7/9;

Both Rhesus positives/3 and 4 carry recessive (allele)/are heterozygous/if Rhesus positive was recessive, all children (of 3 and 4) would be Rhesus positive/recessive;

Question 13

p=0.05

Answer 13

1. There is a probability of 5%/0.05;
2. That difference in frequencies / difference in results are due to chance;

Question 14

What does the Hardy-Weinburg principle predict?

Answer 14

The frequency/proportion of alleles (of a particular gene);

Will stay constant from one generation to the next/over generations / no genetic change over time;

Providing no mutation/no selection/population large/population genetically isolated/mating at random/no migration;

Question 15

Part played by the inner membrane of the mitochondrion in producing ATP

Answer 15

ETC

Electrons transferred down electron transport chain;

Provide energy to take protons/H+ into space between membranes;

Protons/H+ pass back, through membrane/into matrix/through ATPase;

Energy used to combine ADP and phosphate/to produce ATP;

Question 16

How you could estimate the number of blubells in a small woodland

Answer 16

Use a grid / split area into squares/sections;

Method of obtaining random coordinates / numbers, e.g. calculator/computer/random numbers table/random number generator;

Count number/frequency of plants in a quadrat;

Calculate mean/average number (per quadrat/section);

Valid method of calculating total number of bluebells/plants. e.g. mean number of plants per quadrat/section/m2 multiplied by number of quadrats/sections/m2 in wood;

Question 17

Explain why it was important to check the repeatability of the measurements

Answer 17

Increases the reliability of the measurements; 2

If measurements are repeatable, differences less likely to be due to measurement/personal error/ anomalies unlikely;

Question 18

Explain why a statistical test was necessary in analysing the results for the common shrew. Use the terms chance and probability in your answer.

Answer 18

A statistical test) determines the probability of results being due to chance;

Enables null hypothesis/description of null hypothesis to be accepted/rejected;

Determines whether correlation/result is significant;