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Biology Paper 2, May/jun 2010  
Questions:   1 2 3 4 5 6 7 8   Main
General Comments
Weakness/Remedies
Strength












Question 4

(a)List four characteristics which can be genetically transmitted in humans[41 marks}
(b)(i) name two sites each in plants and animals where meiosis occurs.[4 marks]
(ii)State two differences between meiosis and mitosis.[2 marks]
(c)A woman with blood group 'A' (heterozygous) claimed that her son who has blood group '0' was fathered by Mr. James who has blood group 'A' (homozygous). With the aid of suitable genetic diagrams
(i)prove or disprove the woman's claim;
(ii)give reasons to support your answer. [10 marks]

_____________________________________________________________________________________________________
OBSERVATION

This question was not a popu1ar one and many candidates avoided it. Many candidates who
attempted it did not score high marks.
In stating inheritable characters many candidates stated skin, colour, hair colour, eye colour
which earned them just one mark for colour. Some stated blood instead of blood group,
anaemia instead of sickle cell anaemia and so lost marks. Many candidates could correctly
name the site of meiosis in plants but in animals they named gonads rather than testes and
ovary and so lost some marks.
A number of candidates cou1d correctly state the differences between mitosis and meiosis but
many candidates answer did not correspond and so they lost marks. Expected answers include:
DIFFERENCES BETWEEN MITOSIS AND MEIOSIS

MITOSIS

MEIOSIS

Nucleus divides only once

Nucleus divides twice

Number of chromosomes remains the same

Number of chromosomes is halved after

after division/diploid.

division/diploid.

Homologous chromosomes do not associate

Homologous chromosomes associate to form

 

bivalents

Chiasmata are never formed

Chiasmata are formed

Crossing - over never occurs/no exchange of

Crossing - over occurs/exchange of genetic

genetic materials

materials occurs

Daughter cells identical to parent cell

Daughter cells generally different from parent

 

cell;

Two daughter cells are formed

Four daughter cells are formed

Chromosomes form single row at the equator

Chromosomes form double row at the equator

Occurs in somatic cell

Occurs in reproductive cell

Occurs in a sexual reproduction

Occurs in a sexual reproduction

Many candidates performed poorly in question 4(c) on the paternity of woman's child. Most
candidates cou1d not write the genotype of the parents namely AA and AO. They wrote Aa
instead of AO. They would not do the crossing. Many candidates stated that Mr. James was
not the father of the child but could not give reasons for their conclusion .

Expected answers were as follows:

 

 

 

 

 

 

 

WOMAN

x

MAN

 

Blood group

 

A

 

 

A

 


 

 

 

 

 

Phenotypes

 

 

 

 

 

 

Genotype

 

 AO

 

x

AA

 

 

 

Gametes:

 

A

0

A

A

 

 

 

 

 

.

FI GENOTYPES             AO             AO           AA             AA

The Woman's claim is wrong
Reasons
Half their children are heterozygous blood group A and
Halfhomozygous blood group A
No child is group 0

 

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