Application of reproduction and genetics 4.5 Flashcards
What is a genome?
The whole hereditary information of an organism that is enclosed in DNA.
Explain sanger sequencing.
DNA is replicated in the presence of chemically altered versions of the A, C, G and T bases. These bases stop the replication process when they are incorporated into the growing strand of DNA, resulting in varying lengths of short DNA.
How are the strands of DNA organised in sanger sequencing?
They are ordered by size, and by reading the end letters from the shortest to the longest piece, the whole sequence of original DNA is revealed.
What is Next generation sequencing?
It is a new technique that can sequence an entire genome in just a few hours. NGS is enabling scientists to study variation within the human genome amongst 100,000 people in the UK.
What are the ethical issues surrounding the use of genome knowledge?
1: Ownership of genetic information, potential discrimination, social stigmatisation and misuse of the data.
2: The identification of allele sequences has enabled scientists to scan a patient’s DNA sample for mutated sequences and also to compare the sequence of DNA bases in a patient’s gene to a normal version of the gene.
3: The screening of embryo’s has been performed to detect the presence of disorders such as cystic fibrosis, Huntington’s disease and thalassaemia.
What is another genome from other organism that has been sequenced?
The mosquito: The genome of Anopheles gambiae and the Plasmodium parasite that it transmits has been sequenced.
It has been sequenced so that better methods of controlling malaria may be developed.
Describe the process of splicing.
During transcription both exons and introns are initially transcribed into the RNA but the sequences of RNA from the non-coding, intron sections of the gene are removed with the remaining coding sections from the exons being spliced together to form the final messenger RNA that will be translated by ribosomes.
What are short tandem repeats?
Short sequences or blocks of nucleotides that are repeated again and again, they are found in introns.
How are our genetic fingerprints different from one another and specific to an individual?
The number of times an STR is repeated.
Why is a genetic fingerprint not the same as a DNA sequence?
Because it represents only non-coding regions of DNA.
What is the polymerase chain reaction?
It is the semi-conservative replication of DNA in a test-tube. It greatly amplifies the DNA. This makes PCR useful with very small or degraded samples.
DNA is dissolved in a buffer and mixed with what in PCR?
1: Taq polymerase. This is DNA polymerase from the bacterium Thermus aquaticus, which lives in hot springs and hydrothermal vents.
2: Nucleotides containing four DNA bases.
3: Short single-stranded pieces of DNA about 10 bases long, called primers. They are complimentary to the start of the DNA strand and bind to it all, signalling Taq polymerase to start replication.
What are the stages of PCR?
1: Original DNA is heated to 95C, separating it into 2 single strands.
2: Solution is cooled to 55C, which is cool enough for the primers to anneal to the complimentary base sequences on each of the single strands of DNA.
3: Solution is heated to 70*C allowing a thermally stable Taq polymerase to add complimentary nucleotides by forming the phosphodiester bonds in the sugar-phosphate backbone. This is the extension phase. For each initial fragment of double-stranded DNA, two identical double strands are produced.
4: This sequence is repeated many times.
Explain how contamination is a limitation of PCR.
Any DNA that enters the system by accident can be amplified. The contaminating DNA may be air-borne, come from the experimenter or from contaminated reagents. But most contamination comes from previous PCR reactions using the same apparatus.
Explain how Error rate is a limitation of PCR.
All DNA polymerases sometimes insert a nucleotide containing the wrong base. They usually proofread and correct their errors, but Taq polymerase can not do this. It makes an error about once every 9000 nucleotides.
Explain how DNA fragment size is a limitation of PCR.
PCR is most efficient for making DNA about 1000-3000 base pairs long because Taq polymerase cannot correct its errors.
Explain how sensitivity to inhibitors is a limitation of PCR.
Molecules in the sample may act as inhibitors and PCR is very sensitive to them, e.e.:
- Phenolics
- Humic acids in archaeological specimens
- Haem breakdown products
- Traditional blue dye used on denim
Explain how limits on amplification is a limitation of PCR.
At the start of the PCR, the number of DNA molecules made increases exponentially. After about 20 cycles, it slows down: the increase plateaus because:
- Reagent concentrations become limiting
- The enzyme denatures after repeated heating
- DNA in high concentrations causes the single-stranded molecules to base pair with each other rather than with the primers.
What is agarose?
A polysaccharide extracted from seaweed and makes a gel with pores, through which small molecules can move.
How can DNA profiling be vital for paternity testing?
DNA from white blood cells is used to construct DNA profiles. The bands in a child’s DNA fingerprint are compared with the mother’s. Any bands that they share were inherited from her . The remaining strands must have been inherited from the father.
What are the pros of DNA profiling?
1: It does not require an invasive method to obtain a biological sample, as mouth swabs, urine or hair can be used to obtain DNA, rather than blood samples.
2: The technique can be used on samples that would be too small for blood testing.
3: DNA profiling can rule out non-matches of DNA samples, to exonerate people who have been falsely accused.
4: Efforts are being made to store genetic material from people around the world, before isolated groups are intermixed and lost.
What are the cons of DNA profiling?
1: Some people claim that any request for a DNA sample is a violation of an individual’s right to privacy.
2: DNA profiles are held in computer databases, which are vulnerable to misuse and hacking.
3: DNA profiling may produce wrongful convictions if:
- It is used inappropriately to influence juries and judges, especially if they lack an understanding of the significance of the results.
- Errors may occur in the procedure.
What is genetic engineering?
It is a term given to the transfer of ‘foreign’ genetic information from one organism to another.
