Question
The diagram shows the tandem repeats on two different chromosomes for a couple and their children. The number of tandem repeats of the sequence AGAT is shown on chromosome 5 (Chr 5) and the sequence of AGAA on chromosome 18 (Chr 18). One child is adopted.
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(a) Outline the use of tandem repeats in DNA profiling.
(b) Identify the child that is adopted, giving a reason for your answer.
(c) Explain the function of a promoter in DNA.
▶️Answer/Explanation
(a)
Tandem repeats are short sequences of DNA that repeat several times in a row. The number of repeats varies between individuals, and this variation is inherited from parents.
- In DNA profiling, scientists look at these repeat patterns using a method like gel electrophoresis, which separates DNA by size.
- Each person has a unique combination of repeat numbers at different locations in their DNA.
- This makes tandem repeats useful for identifying individuals in paternity testing, criminal investigations, or forensics.
(b)
Child 1 is adopted.
Reason: On chromosome 5, Child 1 has 12 repeats, but neither parent has 12 repeats, so they could not have passed it on. This shows that Child 1 does not share the same biological DNA at that location.
(c)
A promoter is a special region of DNA found before a gene.
- It doesn’t code for a protein but is where RNA polymerase binds to start transcription.
- The promoter helps control when and how much a gene is expressed.
- It also allows the DNA strands to separate so the gene can be copied into mRNA.
