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.
(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.