QUESTION 4:
(a) (i) What are conservative laws? [3 marks]
(ii) State three conservative laws. [3 marks]
(b) (i) State two reasons why animals are poached. [2 marks]
(ii) Name five animals that are commonly poached. [5 marks]
(c) State four effects of excessive use of the forest. [4 marks]
(d) Explain briefly the following terms:
(i) blood transfusion; [2 marks]
(ii) antigen. [2 marks]
The question was not popular among candidates.
Many candidates could not give the correct Parental gamete horizontal (PGH) and Parental game vertical (PGV) thereby getting wrong answers in Offspring (F1) in the punnett square.
In question 4(b), many wrote 9:3:3:1 or 1:3:3:9 as the number of offspring that would have the required phenotypic characters.
Most candidates could not differentiate somatic from reproductive cells and so gave wrong number of chromosomes in question 4(c).
Many candidates loss marks in this question due to poor knowledge of genetics and poor interpretation of the question.
The expected answer is as follows:
(a) Punnett squares of a dihybrid cross
X |
Bt |
Bt |
Bt |
Bt |
bT |
BbTt |
BbTt |
BbTt |
BbTt |
bT |
BbTt |
BbTt |
BbTt |
BbTt |
bT |
BbTt |
BbTt |
BbTt |
BbTt |
bT |
BbTt |
BbTt |
BbTt |
BbTt |
Parental gametes horizontal (PGH): Bt 4x½ [2 marks]
Parental gametes vertical (PGV): bT 4x½ [2 marks]
Offspring (F1) 16x½ [8 marks]
(b) Offspring with:
(i) black fur and short tail – 0
(ii) brown fur and long tail – 0
(iii) black fur and long tail – 16
(iv) brown fur and short tail – 0
(c) Number of Chromosomes in
(i) Pollen grain: 10
(ii) Guard cell: 20
(iii) Ovule: 10
(iv) Root cell: 20