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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 chromosomal composition of an individual. Females possess two X chromosomes (XX), while males possess one X and one Y chromosome (XY). The sex of a child is determined during fertilization:
- The mother contributes an ovum that will always carry an X chromosome.
- The father contributes a sperm that can carry either an X or a Y chromosome.
- If a sperm carrying an X chromosome fertilizes the ovum, the resulting child will be female (XX).
- Conversely, if a sperm carrying a Y chromosome fertilizes the ovum, the resulting child will be male (XY).
- Consequently, there is a 50% chance that the child can be a boy or a girl.
Step 2
Explain how blood grouping is used in paternity testing
Answer
Blood grouping can assist in paternity testing by identifying the possible blood types of the child, mother, and alleged father. The blood group of a child is determined by the alleles received from both parents:
- If the blood group of the mother and the possible father does not match the blood group of the child, the alleged father can be ruled out.
- However, if they match, the man may still be a potential father, and there may be other candidates with the same blood group. Thus, blood grouping alone is not conclusive.
Step 3
Explain how DNA profiling is used in paternity testing
Answer
DNA profiling offers a more definitive method of determining paternity. Each child inherits DNA from both parents. The procedure involves:
- Analyzing the DNA profiles of the mother, child, and possible father.
- Comparing specific DNA bands of the child with those of the potential father.
- If the DNA bands of the child do not correspond to the father's DNA bands, it can rule out paternity.
- Conversely, if the DNA bands match, the possible father is likely to be the biological father, though this does not provide absolute certainty in complex cases.