Use the information below to answer questions (a)(i) and (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]
a)
(i) The possible genotypes of their offspring can be determined using a Punnett square. The female heterozygote for sickle cell has the genotype HbA HbS, and the sickler has the genotype HbS HbS.
|
HbA |
HbS |
| HbS |
HbA HbS |
HbS HbS |
| HbS |
HbA HbS |
HbS HbS |
The possible genotypes of their offspring are HbA HbS (sickle cell trait) and HbS HbS (sickle cell disease).
(ii) The phenotypic ratio of the offspring can be determined from the Punnett square as follows:
- 50% of the offspring will have sickle cell disease (HbS HbS).
- 50% of the offspring will have sickle cell trait (HbA HbS).
b)
A Rhesus negative woman who marries a Rhesus positive man is at risk of developing Rhesus incompatibility. During her first pregnancy, if the fetus is Rhesus positive, some of the fetal blood cells may enter her bloodstream and stimulate her immune system to produce antibodies against the Rhesus factor. In her second pregnancy, if the fetus is also Rhesus positive, her antibodies may cross the placenta and attack the fetal red blood cells, leading to hemolysis (breakdown of red blood cells) and anemia (low levels of red blood cells). This condition is known as hemolytic disease of the newborn (HDN) and can lead to serious complications, including brain damage and even death.
c)
Two examples of features in animals that support Lamarck's theory of use and disuse of body parts are:
- The long neck of giraffes: According to Lamarck's theory, giraffes developed long necks because they stretched their necks to reach higher leaves on trees, and this stretching caused their necks to become longer over time. However, this theory has been disproven by modern genetics, which shows that the long neck of giraffes is actually the result of natural selection acting on random genetic variations.
- The reduced hindlimbs of snakes: According to Lamarck's theory, snakes lost their hindlimbs because they no longer needed them for locomotion, and the disuse of these limbs caused them to gradually shrink and disappear. However, this theory has also been disproven by modern genetics, which shows that the loss of hindlimbs in snakes is actually the result of genetic mutations that have been selected for over time.
d)
Three structures in mammals that are vestigial are:
- The appendix: This is a small pouch attached to the large intestine that may have played a role in digestion in our distant ancestors. However, in modern humans, the appendix appears to have no function and can even cause health problems if it becomes
a)
(i) The possible genotypes of their offspring can be determined using a Punnett square. The female heterozygote for sickle cell has the genotype HbA HbS, and the sickler has the genotype HbS HbS.
|
HbA |
HbS |
| HbS |
HbA HbS |
HbS HbS |
| HbS |
HbA HbS |
HbS HbS |
The possible genotypes of their offspring are HbA HbS (sickle cell trait) and HbS HbS (sickle cell disease).
(ii) The phenotypic ratio of the offspring can be determined from the Punnett square as follows:
- 50% of the offspring will have sickle cell disease (HbS HbS).
- 50% of the offspring will have sickle cell trait (HbA HbS).
b)
A Rhesus negative woman who marries a Rhesus positive man is at risk of developing Rhesus incompatibility. During her first pregnancy, if the fetus is Rhesus positive, some of the fetal blood cells may enter her bloodstream and stimulate her immune system to produce antibodies against the Rhesus factor. In her second pregnancy, if the fetus is also Rhesus positive, her antibodies may cross the placenta and attack the fetal red blood cells, leading to hemolysis (breakdown of red blood cells) and anemia (low levels of red blood cells). This condition is known as hemolytic disease of the newborn (HDN) and can lead to serious complications, including brain damage and even death.
c)
Two examples of features in animals that support Lamarck's theory of use and disuse of body parts are:
- The long neck of giraffes: According to Lamarck's theory, giraffes developed long necks because they stretched their necks to reach higher leaves on trees, and this stretching caused their necks to become longer over time. However, this theory has been disproven by modern genetics, which shows that the long neck of giraffes is actually the result of natural selection acting on random genetic variations.
- The reduced hindlimbs of snakes: According to Lamarck's theory, snakes lost their hindlimbs because they no longer needed them for locomotion, and the disuse of these limbs caused them to gradually shrink and disappear. However, this theory has also been disproven by modern genetics, which shows that the loss of hindlimbs in snakes is actually the result of genetic mutations that have been selected for over time.
d)
Three structures in mammals that are vestigial are:
- The appendix: This is a small pouch attached to the large intestine that may have played a role in digestion in our distant ancestors. However, in modern humans, the appendix appears to have no function and can even cause health problems if it becomes