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 Biology Paper 2, May/jun 2014
 Questions: 1 2 3 4 5 6 Main
Weakness/Remedies
Strength

Question 4

A survey to determine blood groups was carried out on 250 people living a community.
The results are represented in the Table below.

 Blood group Percentage A 8.0 B 14.0 AB 32.8 O 45.2

(a)        (i)         Explain the term co-dominance .       [2 marks]
(ii)        Calculate the number of individuals with co-dominant blood group.     [3 marks]
(iii)       What is the total number of individuals in the Table that are able
to donate blood to an accident victim with blood group B?      [6 marks]

(b)        A man whose blood group is heterozygous A is married to a woman whose
blood group is AB.  With the aid of a genetic diagram, suggest the possible
blood groups of their children.       [9 marks]

_____________________________________________________________________________________________________
OBSERVATION

This was the most unpopular question among the candidates.  The few candidates that
attempted it did so poorly.

(a)(i)  Codominance
Codominance occurs when both the alleles in an heterozygous individual are fully
expressed; that is both alleles exert their effects so that the hybrid has a phenotype;
that is different from what the parents exhibit.

(ii)   Calculation of Individuals with Co dominant blood group
Mention of codominant blood group is AB

Evidence of Calculation

32 .8% of 250
OR
32.8   x 250
100
=   82 individuals/people

(iii)   Total number of individuals that can donate blood  to blood group B
The total number of individuals will be from groups B and O

• 14% of the population is Blood group  B

14% of 250
OR
14   x 250
100
=   35 individuals/people

• 45.2% of the population is blood group O

45.2% of 250

45.2  x 250               =   113 individuals/people
100

• Total number of people          =   113 of group O

35 of group B
148 individuals/people can donate blood to the
accident victim in B
OR

The Total number of individuals from (B and O) blood group B and O

• 14% + 45.2%  =  59.2%
• 59.2% of 250

•

=          148 people/individuals

(b)     Crossing

OR
Punnet Square – scoring/ (Punnet Square)