Use the information below to answer questions 4(a)(i) and 4(a)(ii).
Hb Are presents normal haemoglobin,
HbS represents sickled haemoglobin.
a. A female heterozygote for sickle cell married a sickler. With the aid of a genetic diagram, determine the:
(i) possible genotypes of their offspring; [8 marks]
(ii) phenotypic ratio of the offspring. [2 marks]
b. Explain briefly the reason why a Rhesus negative woman married to a Rhesus positive man might lose her second pregnancy. [5 marks]
c. Name two examples of features in animals that support the theory of use and disuse of body parts as used by Lamarck. [2 marks]
d. List three structures in mammals that are vestigial. [3 marks]
Explanation
(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.