12. Determining relatedness between species Flashcards
What does relatedness mena?
How recently species split from a common ancestor
How can proteins be used to evidence relatedness
- Compared in terms of amino acid sequence
- Species that are more closely related will have less differences in their amino acid sequence corresponding proteins that species that are more closely related
Gene conservation
A particular gene that is present in related species which was passed down by a common ancestor
Comparative genomics
Study of comparing genomes of different species to help clarify the evolutionary history
-More recent common ancestor between two species, the greater the degree of conservation of DNA sequence and position of genes within the genome
Dna hybridisation
DNA dissociates into single stands with high temperatures and as temperature falls single stranded pair up with complementary strands and reform double stranded DNA
Process of DNA hybridisation
- DNA is extracted from cells of two species, purified and cut into fragments 500bp long
- The repeated sequences are removed, leaving the unique genetic info of the DNA gene sequences of the species
- The DNA fragments are made single stranded, mixed and allowed to pair. Some pairing will occur between single strand. paining more complete and stronger when DNA is more similar.
- A measure of similarity is obtained by heating the interspecific DNA double stranded fragments and recording the temperature at which half of them become single stranded again (tm). When the degree of complementary pairing is lower, fewer hydrogen bonds must be broken and tm is lower
- A difference of one degree celsius in Tm corresponds to 1% difference in DNA sequences
How can chromosomes be compared
Looking at banding patterns (number, type and position of bands) and use of chromosome painting
Where did mtDNA originate from?
Nuclear and mtDNA separate evolutionary origin with mtDNA being derived from circular genome of prokaryote engulfed by early ancestors of today’s eukaryotic cells
Why is mtDNA better are comparing than nuclear DNA?
- Inherited from mother so mutations in mtDNA occurring during replication of mtDNA
- Mutations due to sexual reproduction and recombination that are seen in nuclear DNA never occur in mitochondria
- Rate of mutation in mtDNA ten times higher than nuclear DNA
Molecular clock concept
Technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged
Limitations of the molecular clock concept
- It assumes dan mates and amino acid sequences change over time at approximately the same rate
- The molecular clock does not keep perfect time and ticks at different rates for different proteins and genes and even for the same protein in different groups of species
Phylogeny
Evolutionary history of an organism
-Show inferred evolutionary relationships based on morphology molecular similarities and dna sequences
Cladograms
- Based in shared derived characteristics, derived character is a novel feature that can be assumed ti have evolved from an original character present in an ancestral organism
- Even shows extinct organisms, does not show time
Master genes
Regulate the activity of other genes in a coordinated way, shaping embryonic development by acting as a master switch, producing transcription factors that turn other genes on or off
Are master genes conserved
-Yes they are found in almost all eukaryotes. their highly conserved nature indicates their importance in the normal development of an organism (if mutation occurs organisms die)
