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Paternity Testing

This question tests your achievement of Cognitive skill CS2 (part (a)) and Practical and Professional skill PS1 (part (b)).

John and George are brothers. They both claim to be the father of Child A and of Child B. The children are definitely siblings; they have the same mother.

(i) From the data in Table 2, what is the sex of Child A and of Child B. State how you came to your conclusion(s).

(ii) Briefly explain how the alleles that make up the genotype of a child at each locus compare to the alleles in his or her parents' genotypes.

(iii) By analysing the SGM + profiles in Table 2, say which one of the statements 1-4 below is most likely to be true. Explain your answer fully. You should explain any evidence that rules out John or George from being the father of Child A or Child B. (Hint: a good way to tackle the question is to look at the DNA profile of one potential parent, John for example, and then, individually, compare his profile with first Child A and then Child B. Then do the same for the other potential parent. This complete analysis will allow you to answer the question fully.)

1 John is the father of both children.
2 George is the father of both children.
3 John is the parent of one child and George the parent of the other child.
4 Both John and George could be the father of both children.

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Table 2 SGM profiles for two children, A and B, and two brothers, John and
George.

Locus Child a Child b John George
D3S1358 18.19 14,16 14,18 16,18
vWA 15,21 15,21 17,21 17,21
D16S539 11,12 11,13 12,12 12,13
D2S1338 18,23 18,24 18,23 23,24
D8S1179 12,13 12,14 15,15 12,12
D21S11 29.2,32.2 29,31.2129,31.2 29,31.2 29,31.2
D18S51 13,14 13,14 12,16 14,14
D19S433 13,15 13,14 12,15 14,15
THO1 9,9 19,23 25,25 19,24
FGA 19,22 19,23 25,25 19,24
amelogenin XY XX XY XY

(a) John and George are brothers. They both claim to be the father of Child A 
and of Child B. The children are definitely siblings; they have the same 
mother. 


(i) From the data in Table 2, what is the sex of Child A and of Child B. State how you came to your conclusion(s). (No more than 50 words) 


I believe that Child A is male and Child B is female. Amelogenin is a commonly used marker for sex-determination. A result of XY indicates male and a result of XX indicates female.

(ii) Briefly explain how the alleles that make up the genotype of a child at each locus compare to the alleles in his or her parents' genotypes. (50- 
100 words) 


For each locus, a child inherits one allele from his/her father and one from his/her mother. This means that a child and a parent should share (at least one) allele at each ...

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