Observation

 

This was not a popular question among candidates.

Some candidates that attempted the question could not identify the parents as HbA and HbB, those that did, failed to circle and separate the gametes. Some candidates did not even use Hb which was given as symbol for the genotype of the parents and should have been used for the gametes and the offspring which made them lose marks.
Some of the candidates did not put the cross sign (x) between the parental genotypes; some even failed to cross the gametes appropriately. All these accounted for huge losses of marks.

Candidates failed to explain the reason why a Rhesus negative woman married to a Rhesus positive man might lose her second pregnancy.
Some candidates could not also name the features in animals that support the theory of use and disuse of body parts as used by Lamarck.
Many candidates could list the structures in mammals that are vestigial although some lost marks to careless and poor spellings of the structures.

The expected answers are:

4(a) i Genetic diagram


Note: Punnett square should be accepted;
Gametes must be circled and spread apart to score;
If the crossing is wrong the F1 generation does not score;
If cross sign (X) is absent, no score.

ii Phenotypic ratio
2:2 or 1:1/Ratio of sickler to non-sicklers.

b Reasons why a rhesus negative woman married to a rhesus positive man might lose her second pregnancy
- Rhesus negative mother has no antigen on the surface of her Red Blood Cells/RBC;
- the husband has antigen on his RBC;
- during her first pregnancy, the child carries positive Rhesus factor;
- the Rhesus factor enters the mother’s blood stream;
- due to rupture of the placenta, blood seeps into the mother’s blood;
- causing it to develop anti-Rhesus antibodies;
- causing agglutination in small proportion of foetal blood cells;
- in the second pregnancy, the child might be Rhesus positive;
- the child carrying Rhesus positive suffers massive destruction of red blood cells/erythroblastosis fetalis;
- which might result into miscarriage of the second child.

c Examples of features in animals that support the theory of use and disuse of body parts as used by Lamarck
- long neck in Giraffe;
- smaller wings in Penguins;
- lost legs of snakes;
- long legs of Heron;
- webbed feet of ducks/frogs/geese.

d Vestigial organs in mammals
- appendix in humans;
- pelvic and leg bones in whale;
- reduced coccyx in man/caudal vertebrae;
- pyramidalis nasi (extrinsic) muscle/muscles of the forehead;
- posterior auricular muscles to move the ear/pinna;
- erector muscle;
- nipples in males;
- sinuses;
- tonsils;
- wisdom teeth;
- hairs on the chest.