Genetic fingerprinting

RNA and DNA are polynucleotides.

Two types of RNA are messenger RNA and transfer RNA.

The table shows some properties of these two types of RNA.

Place ticks (✓) in the correct boxes to indicate which properties are true for each type of RNA.

Outline how gene expression is regulated within cells at the post‑transcriptional level.

A student writes this method for extracting DNA from animal cells:

1. Grind the sample of cells using a mortar and pestle.

2. Mix the sample with detergent.

3. Add ethanol to precipitate the DNA from the solution.

4. Spool the DNA onto a glass rod.

Another student suggests that step 1, grinding the sample of cells, is unnecessary.

Explain why step 1 is unnecessary.

State one other step that the student should include in the method and explain why this step is necessary.

Electrophoresis is used to separate fragments of DNA so that the separated DNA fragments can be compared and analysed.

The diagram shows an electrophoresis box. Solutions of DNA samples have been added to three of the wells in the box.

Solutions containing

State two other solutions that should be added to the box before performing electrophoresis and explain the purpose of each solution.

Electrophoresis can be used to detect disease‑causing alleles, such as the mutant HBB allele that causes sickle cell disease.

Restriction enzymes are used to produce fragments of HBB alleles for analysis by electrophoresis.

These restriction enzymes:

• produce one fragment when the sickle cell HBB allele is present

• produce two smaller fragments when the normal HBB allele is present.

The diagram shows the results of electrophoresis of DNA samples from five people. It only shows DNA fragments from the HBB gene.

State the lane numbers that indicate:

• a genotype that is homozygous for the sickle cell HBB allele

• a genotype that is homozygous for the normal HBB allele

• a heterozygous genotype for the HBB gene.

Homozygous sickle cell........

Homozygous normal........

Bacterial cells can be used for genetic engineering.

A donor gene is placed into a plasmid, which is taken up by a bacterial cell.

This process is inefficient. Not all plasmids form recombinant DNA with the donor gene, and only a small percentage of bacterial cells take up plasmids.

A scientist estimates that 40% of their plasmids join to the donor gene to form recombinant DNA.

One in 2500 bacterial cells takes up a plasmid to form a transformed bacterial cell.

The scientist uses 1 × 10⁹ bacterial cells.

Calculate the number of cells that take up a plasmid containing the donor gene.

The percentage of plasmids that are taken up by bacterial cells is known as the transformation efficiency.

Suggest one factor that scientists could change to improve transformation efficiency.

DNA profiling is an important technique with many uses.

The steps involved in creating a DNA profile can be outlined as follows:

1. DNA extraction

2. Digestion

3. Separation

4. Analysis

DNA profiling is used in the investigation of crime and in paternity cases.

State one other use of DNA profiling.

When creating a DNA profile from a crime scene, an intermediate step between DNA extraction and digestion, known as PCR, is usually carried out.

The technique of PCR involves a cycle of changes in temperature, shown in the graph.

Name the technique known as PCR.

Outline the process of PCR, with reference to steps X, Y and Z.

Explain why a temperature of 72–75 °C is used for step Z.

Suggest why a PCR step is usually necessary when creating a DNA profile from a crime scene sample in particular.

This is part of a DNA profile for six loci from a sample of DNA found at a crime scene (E), and DNA from a potential suspect (S).

Suggest why some loci have two peaks but some have only one.

Using the evidence in the DNA profile it was claimed that suspect S had been at the crime scene.

Explain how strongly the evidence supports this claim.

Some students incubated plasmid DNA with a restriction enzyme.

After 24 h they used gel electrophoresis to analyse the products of the incubation.

Which option shows the correct procedure for gel electrophoresis?

A Load the sample onto agarose gel → apply voltage for a set time → photograph the gel

B Load the sample onto agarose gel → apply voltage for a set time → stain the gel → photograph the gel

C Photograph the agarose gel → load the sample onto gel → apply voltage for a set time → stain the gel

D Stain the agarose gel → apply voltage for a set time → load the sample onto agarose gel → photograph the gel

Your answer

Agammaglobulinemia and Vici syndrome are both genetic diseases.

Agammaglobulinemia results in a lack of mature B lymphocytes in a person’s blood.

Suggest and explain one symptom of agammaglobulinemia.

Fig. 4 shows the inheritance pattern of agammaglobulinemia in a family.

What conclusions can you draw about the location and nature of the allele responsible for causing agammaglobulinemia? Explain your conclusions.

Vici syndrome is a genetic disease that shows a recessive inheritance pattern. The allele responsible for Vici syndrome is found on chromosome 18.

Two carriers of Vici syndrome have six children.

Calculate how many of the six children you would expect to:

• have Vici syndrome

• be carriers of Vici syndrome.

A daughter of these parents and a male carrier of Vici syndrome have a child.

Calculate the probability of the child having Vici syndrome.

DNA profiling can be used to analyse the risk of inheriting conditions such as agammaglobulinemia and Vici syndrome.

To produce a DNA profile, DNA first needs to be purified.

Explain why a protease enzyme is added to the mixture during the DNA purification process.

DNA samples can be amplified using the polymerase chain reaction (PCR).

In theory, how many fragments of DNA might be present after 12 cycles of PCR?

Assume one DNA fragment was present at the beginning of the PCR process. Represent your answer as a log₁₀ value.

Suggest why the figure you calculated in (ii) may not be achieved in practice.

State the name of the enzyme used in PCR to synthesise new DNA strands.

DNA fragments are separated to produce a DNA profile using electrophoresis.

A student wrote the following description of the electrophoresis procedure:

We will set up an agarose gel plate and place the DNA samples in the wells at the cathode. Voltage will be passed through the gel for one minute. The gel will then be placed in purified water and we will be able to see the banding pattern of each DNA sample.

Describe two changes you would make to the student’s procedure and explain how these changes would improve electrophoresis.

Fig. 1.1 shows the structure of the amino acid leucine.

On Fig. 1.1, draw a circle around the R group of leucine.

Students used thin layer chromatography to separate leucine from other amino acids. The chromatogram they produced is shown in Fig. 1.2.

What can you conclude about the chemical properties of leucine and amino acid X?

Amino acid Z was in the mixture analysed by the students. It is not shown on the chromatogram in Fig. 1.2. Amino acid Z has an R_f value that is 0.20 lower than that of amino acid Y.

Place a dot on the chromatogram in Fig. 1.2 to show the distance moved by amino acid Z.

Show your working.

Thin layer chromatography can also be used to separate photosynthetic pigments.

State a material that can be used as the stationary phase in thin layer chromatography.

State the precise location of photosynthetic pigments in a chloroplast.

When sequencing DNA, fragments of DNA are separated by electrophoresis.

Describe three differences between the process of thin layer chromatography and the form of electrophoresis used to sequence DNA.