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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 presence of specific sex chromosomes:
- Females have two X chromosomes (XX), while males carry one X and one Y chromosome (XY).
- The sex of the child is determined by the combination of the gametes from the mother and the father.
- An ovum from the mother will always carry an X chromosome.
- A sperm from the father will either carry an X chromosome or a Y chromosome.
The outcomes of fertilization can be summarized as follows:
- If a sperm carrying the X chromosome fertilizes the ovum with an X chromosome, the result is a female (XX).
- If a sperm carrying the Y chromosome fertilizes the ovum, the outcome is a male (XY).
Thus, there is a 50% chance that the child can be either a boy or a girl.
Step 2
Explain how blood grouping is used in paternity testing
Answer
Blood grouping can provide insight into paternity through the alleles inherited from both parents:
- The blood group of the child is determined by the blood groups of the mother and the possible father.
- If the mother's blood group is known, the potential blood groups of the child can also be inferred based on the father's group.
- For example, if the blood types suggest that a potential father cannot have produced the child's blood type, he can be ruled out as the father.
- Conversely, if the child's blood group is consistent with possible blood types from the mother and potential father, it does not definitively prove parentage.
Step 3
Explain how DNA profiling is used in paternity testing
Answer
DNA profiling is a more definitive method of determining paternity:
- A child inherits DNA from both parents, and this DNA can be compared through profiling.
- DNA bands from both the mother and the father can be examined to see if the child's bands match.
- If the child's DNA matches both parents' DNA bands, paternity is confirmed.
- However, if there are DNA bands in the child's profile that do not correspond with either parent's, the individual cannot be the biological child of the tested parents.
Thus, DNA profiling provides a high level of certainty in paternity testing.