Photo AI
Sometimes the paternity of a son or a daughter is disputed - NSC Life Sciences - Question 4 - 2019 - Paper 2
Question 4
Sometimes the paternity of a son or a daughter is disputed. Describe sex determination in humans and explain how blood grouping and DNA profiling are used in patern... show full transcript
Worked Solution & Example Answer:Sometimes the paternity of a son or a daughter is disputed - NSC Life Sciences - Question 4 - 2019 - Paper 2
Step 1
Describe sex determination in humans
Answer
In humans, sex determination is based on the presence of specific sex chromosomes:
- Females possess XX chromosomes, while males possess XY chromosomes.
- Females produce an ovum (egg) that will always carry the X chromosome.
- Males produce sperm that will carry either an X or Y chromosome:
- If a sperm carrying the X chromosome fertilizes the ovum, a female child (XX) will result.
- If a sperm carrying the Y chromosome fertilizes the ovum, a male child (XY) will result.
Thus, the sex of the child is determined by the father's contribution, having a 50% chance of resulting in either a boy or a girl.
Step 2
Explain how blood grouping is used in paternity testing
Answer
Blood grouping is determined by the alleles received from both parents:
- The blood group of the child can be inferred from the blood groups of the mother and possible father.
- If the blood group of the child does not match the blood group of the alleged father, he is eliminated as a potential father.
- However, if the blood group matches, it does not conclusively prove paternity because both the child and possible father may share the same blood group.
Step 3
Explain how DNA profiling is used in paternity testing
Answer
DNA profiling involves comparing genetic markers or bands from the child, mother, and possible father:
- A child inherits DNA from both parents.
- The DNA profiles of the mother and possible father are analyzed to determine whether the child inherits the expected bands.
- If there are discrepancies in the DNA bands, this could indicate that the possible father is not the biological father.
- Conversely, if all DNA bands from the child match those of the possible father, this supports paternity.