4. Genome Sequencing and Immunology Flashcards
Species can be classified based on similarities and differences in their genes.
This can be done by:
Comparing their DNA sequences.
Comparing mRNA sequences (introns removed)
Or by looking at their proteins – which are coded for by their genes and comparing the primary structures.
Organisms that are more closely related will have more similar DNA, mRNA and proteins than distantly related organisms.
Gene technologies give more accurate estimates of genetic diversity and make comparisons of genetic diversity easier to carry out.
What colours are the DNA strands in species A?
What cause the 2 strands of DNA to separate ?
What allows the hydrogen bonds to reform?
What is the hybrid DNA made of?
Do all the hydrogen bonds reform? – explain your answer
Why are the new DNA hybrid strands gradually heated up again?
What colours are the DNA strands in species A?
Blue & yellow
What cause the 2 strands of DNA to separate ?
Heat breaks the weak hydrogen bonds between the nitrogenous bases and the strands separate
What allows the hydrogen bonds to reform?
When cooled – hydrogen bonds reform – by complimentary bas pairing –more stable energetically
What is the hybrid DNA made of?
A strand of DNA from each organism
Do all the hydrogen bonds reform? – explain your answer
No only where the sequence of DNA bases are complementary
Why are the new DNA hybrid strands gradually heated up again?
To find the temperature that the DNA hybrid strands will separate
DNA Hybrisation
- DNA from different species is collected and separated into single strands by heating it, heating breaks the weak hydrogen bonds between the nitrogenous bases (A=T and C with G)
- We then mix the separated strands.
- Where base sequences are complementary hydrogen bonds reformed between the separated strands. Some original double helices will form and some hybrid DNA forms: from 1 DNA strand from each species (A&B)
- The more hydrogen bonds that form the more similar the DNA bases sequences in each of the DNA strands (A&B)
- The DNA is then gradually heated a second time to separate the Hybrid DNA strands again, and the temperature of complete separation recorded.
- The greater temperature needed to separate the DNA hybrid strands, the more closely related the 2 species (A& B)a higher temperature will be needed to separate the strands, as there will be more hydrogen bonds to break.
DNA sequencing
Due to mutations, the DNA that codes for a particular protein in an organism alive today is slightly different from the DNA that coded for the same protein in its distant relative.
Closely related species will have a higher % of similarity in their DNA base order e.g. humans and chimps share about 94%, humans and mice share about 85%
Why does the figure 100% feature in the table?
Which species are most closely related?
Which species are least closely related?
There is 100% hybridisation between DNA strands from an individual of a particular species
C&D
A&C
Comparing mRNA sequences to classify species
DNA contains sections of non-coding bases sequences which often form multiple repeats between genes. Then within genes there are non-coding sequences of bases called introns, the introns are spliced out leaving, start & stop codons and the exons code for polypeptide chains.
Describe the differences between DNA and mature mRNA sequences (3)
DNA has multiple repeated sequences of bases between genes
DNA has promoter and terminator sequences at the star and the end of the gene
DNA has introns within a gene
Where are DNA and mRNA found in the cell?
DNA is found in the nucleus only,
mRNA travels between the nucleus and cytoplasm where it binds to ribosomes
How many copies of DNA and mRNA are found within a single cell?
There is only one copy of the DNA double helix unless the cell is dividing when there can be 2 copies (2 sister chromatids)
At any one time there can be many copies of mRNA, if however, a particular gene is not being expressed there may be no copies.
- Using your answers suggest why it is easier to compare mRNA base sequences when trying to classify organism
There is more mRNA available, it is more easily accessible – extracted from the cytoplasm, it is shorter so quicker to sequence, it has had non-coding sequences removed so the sequence can be used to determine polypeptide primary structure
- Comparing amino acid sequences
1.What is serum?
- What is injected into the rabbit?
- Why does the rabbit produce antibodies?
- What does the rabbit produce antibodies against? 5.Rabbit antibodies are specific-what does that mean?
- When the rabbit anti-human antibodies are mixed with the human serum what happens?
- If you mix rabbit anti human antibodies with chimpanzee serum what happens?
- Which of the organisms in the diagram are least closely related to humans? Explain. your answer.
- Serum is another name for blood plasma
- Human serum(plasma) is injected into the rabbit
- The serum contains plasma proteins which will act as antigens stimulating an immune response.
- The rabbit antibodies are produced against the human’s plasma proteins.
- Rabbit antibodies will only bind to 1 type of antigen as their binding sites are only complimentary to the shape of 1 antigen, to form antibody antigen complexes..
- Antibodies bind antigen and cause agglutination (clumping) which is seen as a solid precipitate
- High degree of precipitation between anti human Ab and chimpanzee plasma proteins, showing that humans and chimps are very closely related
- Dogs and humans are least closely related, because you have the least
precipitation formed
The scientists obtained DNA from otters that were alive before hunting started.
Suggest one source of this DNA.
Bone / skin / preserved remains / museums;
What can you conclude about the effect of hunting on genetic diversity in otters? Use data from the figure above to support your answer.
1.(Hunting) reduced population size(s), so (much) only few alleles left;
Accept bottleneck
2.Otters today from one / few surviving population(s);
Accept founder effect
3.Inbreeding;
Some populations of animals that have never been hunted show very low levels of genetic diversity.
Other than hunting, suggest two reasons why populations might show very low levels of genetic diversity
1.Population might have been very small / genetic bottleneck;
2.Population might have started with small number of individuals / by one pregnant female / founder effect;
3.Inbreeding;
