Evidence for Evolution - DNA Evidence

Describe the relation fo all living things with DNA

All living things have the same DNA code, adding to hypothesis that all have common ancestor. The sequence of bases in DNA of living things varies.

What causes gain and loss of genes

New genes gained by mutation, others lost by natural selection, genetic drift or some other process.

DNA in more related compared to less related species:

Species more distantly related have more differences in DNA, whereas species more closely related share greater portion of their DNA.

define comparative genomics:

comparison of genome sequences of different species

what does comparative genomics do?

It helps identify genes that are preserved among species, as well as genes that give each organism its unique characteristics.

What is a genome?

complete set of DNA in each cell of an organism

what is DNA hybridisation

technique measuring degree of genetic similarity between DNA sequences

Explain the process used for DNA Hybridisation:

DNA strands to be compared are mixed, incubated and allowed to reform as hybrid double-stranded DNA. DNA unzips at 94ᵒC {in humans?}. Hybridised sequences with a high degree of similarity will bind more firmly, and therefore will require more energy (in the form of heat) to separate them. [If more closely related species, unzip at 80ᵒC]

what observation about non-coding sequences in DNA makes sense if related species have evolved from a common ancestor

Non-coding sequences of bases in DNA show more similarities with more closely related species.

what are endogenous retroviruses?

Viral sequence that has become part of organism’s genome. Are stretches of apparently non-functional DNA.

what does a retrovirus do when entering a cell?

Upon entering a cell, retrovirus copies its RNA genome into DNA (reverse transcription). DNA then becomes inserted into one of the host cell’s chromosomes

what makes a retrovirus, endogenous?

Only becomes endogenous if it inserts into a cell whose chromosomes will be inherited by the next generation (ovum or sperm)

Impact of endogenous retrovirus on future generations

Offspring of infected individual will then have a copy of the ERV, in same place, in same chromosome, in every single one of their cells. All subsequent generations will also have a copy of the ERV in the same location.

How can we use ERV to make evolutionary comparisons?

Any retrovirus that became inserted into the genome of common ancestor would be inherited by both chimpanzees and humans at exactly same location in the chromosome. 16 instances of human ERV’s match exactly with Chimpanzee ERV’s. Experimentation gives very strong indication that all primates shared a common ancestor, diverging at different periods.

what is mitochondria?

organelles in cell where aerobic phase of respiration occurs to release energy for use by the cell 

what is mtDNA

DNA found in mitochondria, in the form of small circular molecules

reason why is mtDNA extracted for comparision over nDNA (nuclear DNA)

• Most cells contain large numbers of mitochondria & therefore usually have between 500-1000 copies of mtDNA, making it a lot easier to find & extract than nDNA

compare the nDNA and mtDNA

• nuclear DNA comes from both parents whereas mitochondrial DNA comes just from the mother

• mtDNA has higher rate of mutation than nuclear DNA

Explain how mitochondrial DNA is used as evidence for evolution

Because of the mutations (high rate of mutations in them), human mtDNA has been slowly diverging from mtDNA of original female ancestors. The amount of mutation is roughly proportional to the amount of time that has passed

• use similarity between mtDNA to provide estimate of closeness of their relationship through maternal ancestors

Identical mtDNA = closely related

in what circumstances is mtDNA most useful?

useful when comparing individuals within a species and for species that are closely related