Annealing is the PCR stage where the mixture is cooled to about 55 °C so that primers bind to their complementary sequences on each separated DNA strand.

What are the three stages of each PCR cycle?

Denaturation ( 95 °C — the two DNA strands separate), annealing ( 55 °C — primers bind), and extension (~72 °C — DNA polymerase builds new complementary strands).

During the extension stage of PCR, the enzyme adds free nucleotides to build a new DNA strand from each primer.

During the extension stage of PCR, the enzyme Taq polymerase adds free nucleotides to build a new DNA strand from each primer.

Give two uses of the polymerase chain reaction (PCR).

PCR is used to amplify tiny DNA samples for uses such as forensic analysis of crime-scene DNA , diagnosing genetic disorders or infections , and providing amplified DNA for DNA profiling .

Polymerase chain reaction (PCR)

Polymerase chain reaction (PCR) is an in vitro method of DNA replication , producing billions of identical copies of a specific DNA fragment in a short time.

A PCR reaction requires DNA, primers, DNA polymerase, free nucleotides, and a solution.

A PCR reaction requires DNA, primers, DNA polymerase, free nucleotides, and a buffer solution.

What is the role of primers in PCR?

Primers are short single-stranded DNA sequences that bind to the 3’ ends of the DNA to define the region to be amplified and provide a starting point for DNA polymerase.

True or False? Taq polymerase is used in PCR because it denatures at high temperatures.

False. Taq polymerase is used in PCR because it does not denature at high temperatures , making it ideal for the cycle's denaturation step.

During PCR, the denaturation stage occurs at °C to separate the DNA strands, while the extension stage is at °C.

During PCR, the denaturation stage occurs at 95 °C to separate the DNA strands, while the extension stage is at 72 °C.

What happens to the amount of DNA after each PCR cycle?

Each PCR cycle doubles the amount of DNA , leading to exponential amplification of the DNA fragment.

A thermal cycler is the machine used in PCR that rapidly changes the temperature to run the denaturation, annealing and extension stages of each cycle.

Gel electrophoresis is a technique used to separate DNA, RNA, or proteins based on their size and charge by moving them through a gel in an electric field .

DNA fragments are created using enzymes called that cut DNA at specific restriction sites.

DNA fragments are created using enzymes called restriction endonucleases that cut DNA at specific restriction sites.

What causes DNA molecules to move towards the anode during gel electrophoresis?

DNA molecules are negatively charged due to their phosphate groups , so they move towards the positive anode in an electric field.

An agarose gel is a type of gel used in electrophoresis that forms a porous matrix, allowing separation of molecules by size.

True or False? Smaller DNA fragments move more slowly through the gel than larger fragments during electrophoresis.

False. Smaller DNA fragments move faster and further through the gel than larger fragments.

The DNA samples are transferred into the using a micropipette, ensuring that a sample of DNA standard is loaded into the first one.

The DNA samples are transferred into the wells using a micropipette, ensuring that a sample of DNA standard is loaded into the first one.

What is the purpose of adding probes after gel electrophoresis is complete?

Probes are added to bind to specific DNA fragments, making them visible as bands on the gel using radioactive or fluorescent labels.

Why does gel electrophoresis produce a unique pattern of bands for every individual?

Different individuals have different numbers of VNTR repeats , so restriction enzymes cut their DNA into fragments of different lengths, producing a unique banding pattern .

A DNA profile is a series of DNA bands of different length produced using gel electrophoresis and visible by radioactive or fluorescent labels.

What is the purpose of adding radioactive or fluorescent labels in gel electrophoresis for DNA profiling?

Radioactive or fluorescent labels allow the bands of DNA of different lengths to be seen after gel electrophoresis, making the DNA profile visible.

A child will share of their DNA with each parent due to fertilisation.

A child will share half of their DNA with each parent due to fertilisation.

During a paternity test, what does it mean if many bands in a child's DNA profile match a candidate's profile?

If many bands match between the child and a candidate , it indicates that the candidate is the most likely biological father.

True or False? The more bands that match between DNA profiles, the closer the genetic relationship between the individuals.

True. A higher number of matching bands between DNA profiles indicates a greater genetic similarity and a closer relationship.

A short tandem repeat (STR) is a short, non-coding repeated DNA sequence also known as a microsatellite , used in DNA profiling.

Why does analysing more regions of short tandem repeats make DNA profiling more reliable in forensic science?

Analysing more STR regions reduces the chance that closely related individuals will have identical profiles, making the evidence more reliable in court.

Breeding between closely related individuals is known as , and it can lead to a gene pool in a population.

Breeding between closely related individuals is known as inbreeding , and it can lead to a smaller gene pool in a population.

Forensics is the use of science in the investigation of criminal activities .

Determining the of death is a very important component of forensic science.

Determining the time of death is a very important component of forensic science.

What factors must be established to accurately estimate the time of death?

To accurately estimate the time of death, forensic scientists must establish factors such as the extent of decomposition , stage of succession , forensic entomology , body temperature and the degree of muscle contraction .

What are decomposers ?

Decomposers are organisms such as bacteria and fungi that break down dead tissue during decomposition.

As decomposition progresses, the skin may appear in colour, and later, blisters and falls off.

As decomposition progresses, the skin may appear greenish in colour, and later, blisters and falls off.

What is the difference between succession in ecology and succession on a dead body?

In ecology, early species are out-competed and disappear as the system matures, but on a dead body , successive waves of species colonise the body and are replaced as decomposition progresses.

How can forensic entomology help estimate time of death?

Forensic entomology can help estimate time of death by examining the species of insects present and their stage of development , which indicate how long the body has been colonised since death.

After death, the body temperature drops by to °C per hour until it matches the environment.

After death, the body temperature drops by 1.5 to 2.0 °C per hour until it matches the environment.

How does the degree of muscle contraction help estimate the time of death?

After death, muscles gradually stiffen in a process called rigor mortis , which begins a few hours after death and later wears off. The degree of muscle contraction therefore indicates how long ago death occurred.

International A Level (IAL)BiologyEdexcelFlashcards6. Microbiology, Immunity & ForensicsForensics

Forensics (Edexcel International A Level (IAL) Biology): Flashcards

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Annealing
Annealing is the PCR stage where the mixture is cooled to about 55 °C so that primers bind to their complementary sequences on each separated DNA strand.
What are the three stages of each PCR cycle?
Denaturation (_{95 °C — the two DNA strands separate),}_annealing₍55 °C — primers bind), and extension (~72 °C — DNA polymerase builds new complementary strands).
During the extension stage of PCR, the enzyme adds free nucleotides to build a new DNA strand from each primer.
During the extension stage of PCR, the enzyme Taq polymerase adds free nucleotides to build a new DNA strand from each primer.
Give two uses of the polymerase chain reaction (PCR).
PCR is used to amplify tiny DNA samples for uses such as forensic analysis of crime-scene DNA, diagnosing genetic disorders or infections, and providing amplified DNA for DNA profiling.
Polymerase chain reaction (PCR)
Polymerase chain reaction (PCR) is an in vitro method of DNA replication, producing billions of identical copies of a specific DNA fragment in a short time.
A PCR reaction requires DNA, primers, DNA polymerase, free nucleotides, and a solution.
A PCR reaction requires DNA, primers, DNA polymerase, free nucleotides, and a buffer solution.
What is the role of primers in PCR?
Primers are short single-stranded DNA sequences that bind to the 3’ ends of the DNA to define the region to be amplified and provide a starting point for DNA polymerase.
True or False?
Taq polymerase is used in PCR because it denatures at high temperatures.
False.
Taq polymerase is used in PCR because it does not denature at high temperatures, making it ideal for the cycle's denaturation step.
During PCR, the denaturation stage occurs at °C to separate the DNA strands, while the extension stage is at °C.
During PCR, the denaturation stage occurs at 95 °C to separate the DNA strands, while the extension stage is at 72 °C.
What happens to the amount of DNA after each PCR cycle?
Each PCR cycle doubles the amount of DNA, leading to exponential amplification of the DNA fragment.
Thermal cycler
A thermal cycler is the machine used in PCR that rapidly changes the temperature to run the denaturation, annealing and extension stages of each cycle.
Gel electrophoresis
Gel electrophoresis is a technique used to separate DNA, RNA, or proteins based on their size and charge by moving them through a gel in an electric field.
DNA fragments are created using enzymes called that cut DNA at specific restriction sites.
DNA fragments are created using enzymes called restriction endonucleases that cut DNA at specific restriction sites.
What causes DNA molecules to move towards the anode during gel electrophoresis?
DNA molecules are negatively charged due to their phosphate groups, so they move towards the positive anode in an electric field.
Agarose gel
An agarose gel is a type of gel used in electrophoresis that forms a porous matrix, allowing separation of molecules by size.
True or False?
Smaller DNA fragments move more slowly through the gel than larger fragments during electrophoresis.
False.
Smaller DNA fragments move faster and further through the gel than larger fragments.
The DNA samples are transferred into the using a micropipette, ensuring that a sample of DNA standard is loaded into the first one.
The DNA samples are transferred into the wells using a micropipette, ensuring that a sample of DNA standard is loaded into the first one.
What is the purpose of adding probes after gel electrophoresis is complete?
Probes are added to bind to specific DNA fragments, making them visible as bands on the gel using radioactive or fluorescent labels.
Why does gel electrophoresis produce a unique pattern of bands for every individual?
Different individuals have different numbers of VNTR repeats, so restriction enzymes cut their DNA into fragments of different lengths, producing a unique banding pattern.
DNA profile
A DNA profile is a series of DNA bands of different length produced using gel electrophoresis and visible by radioactive or fluorescent labels.
What is the purpose of adding radioactive or fluorescent labels in gel electrophoresis for DNA profiling?
Radioactive or fluorescent labels allow the bands of DNA of different lengths to be seen after gel electrophoresis, making the DNA profile visible.
A child will share of their DNA with each parent due to fertilisation.
A child will share half of their DNA with each parent due to fertilisation.
During a paternity test, what does it mean if many bands in a child's DNA profile match a candidate's profile?
If many bands match between the child and a candidate, it indicates that the candidate is the most likely biological father.
True or False?
The more bands that match between DNA profiles, the closer the genetic relationship between the individuals.
True.
A higher number of matching bands between DNA profiles indicates a greater genetic similarity and a closer relationship.
Short tandem repeat
A short tandem repeat (STR) is a short, non-coding repeated DNA sequence also known as a microsatellite, used in DNA profiling.
Why does analysing more regions of short tandem repeats make DNA profiling more reliable in forensic science?
Analysing more STR regions reduces the chance that closely related individuals will have identical profiles, making the evidence more reliable in court.
Breeding between closely related individuals is known as , and it can lead to a gene pool in a population.
Breeding between closely related individuals is known as inbreeding, and it can lead to a smaller gene pool in a population.
Forensics
Forensics is the use of science in the investigation of criminal activities.
Determining the of death is a very important component of forensic science.
Determining the time of death is a very important component of forensic science.
What factors must be established to accurately estimate the time of death?
To accurately estimate the time of death, forensic scientists must establish factors such as the extent of decomposition, stage of succession, forensic entomology, body temperature and the degree of muscle contraction.
What are decomposers?
Decomposers are organisms such as bacteria and fungi that break down dead tissue during decomposition.
As decomposition progresses, the skin may appear in colour, and later, blisters and falls off.
As decomposition progresses, the skin may appear greenish in colour, and later, blisters and falls off.
What is the difference between succession in ecology and succession on a dead body?
In ecology, early species are out-competed and disappear as the system matures, but on a dead body, successive waves of species colonise the body and are replaced as decomposition progresses.
How can forensic entomology help estimate time of death?
Forensic entomology can help estimate time of death by examining the species of insects present and their stage of development, which indicate how long the body has been colonised since death.
After death, the body temperature drops by to °C per hour until it matches the environment.
After death, the body temperature drops by 1.5 to 2.0 °C per hour until it matches the environment.
How does the degree of muscle contraction help estimate the time of death?
After death, muscles gradually stiffen in a process called rigor mortis, which begins a few hours after death and later wears off. The degree of muscle contraction therefore indicates how long ago death occurred.

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