determining relatedness between species Flashcards
how can relatedness be determined?
- molecular homology
- phylogenetic trees
what does molecular homology look at?
- molecules
- amino acids
- molecular clocks
- dna
how is relatedness determined using molecules
Very similar proteins, chromosomes or DNA suggest a recent common ancestor (thousands, millions)
Mutations accumulate overtime and once similar DNA diverges
Occasionally mutations are not repaired before mitosis and become a part of the genome
differences in amino acid sequences
As species diverge they begin accumulating differences in amino acid sequences in proteins
More time = more differences
Due to degeneracy not all changes in nucleotides cause changes in amino acids
Even a change in amino acid may not lead to a change in phenotype
Effects of amino acid substitution depend on how biochemically similar they are- size, hydrophobicity and charge
Conservative substitution: amino acid is swapped for a biochemically similar one and does not cause a change in protein.
Semi-conservative substitution: amino acid is swapped for one with similar shape but different biochemical properties, possibly leading to change in protein structure and function.
Non-conservative substitution: substitution of a very different amino acid which leads to major changes in structure and function.
Nucleic acid comparison is more accurate than comparing the amino acid sequence and easier and cheaper now too
Amino acid differences in cytochrome c between organisms is used
Cytochrome c is part of ETC and essential to organisms’ survival
what is a molecular clock? how is it used?
Molecular clock: technique that uses the rate of the accumulation of mutations in DNA to calculate how long ago organisms diverged from one another.
States that changed in DNA and proteins are constant over time and different linages
Calibrated using evidence from fossil record
Number of DNA differences are compared to calibrate the clock with the dates of branch points
what are limitations of molecular clocks?
Assumption that genetic changes are constant
For genetic changes to occur at a constant rate, they need to be neutral and not be affected by natural selection
And DNA regions that code for phenotype are under natural selection and will change according to environment so mutations in protein-coding DNA will not be constant
Some sections of DNA (in the same organism) mutate at different rates- mutations to important genes will mutate slower than those of less important genes
Overestimate time in recent fossils
Underestimate time in old fossils
how can mitochondrial dan be used as a molecular clock?
Passed through maternal line
Mutations accumulate overtime
Does not have as good repair mechanisms as nuclear DNA so mutation rate is usually higher
Can be used as a molecular clock in relatively closely related species while nuclear DNA compares older linages
Easier to get a lot of mtDNA because cells have many mitochondria
what techniques can be used for looking at genetic differences?
dna hybridisation
sequencing dna
how does dna hybridisation work?
Heat double stranded DNA and hydrogen bonds break between complementary strands
When cooled the complementary bases match up again
If single strands from two species are mixed a hybrid double-stranded DNA is formed
steps:
Gene probes isolate a gene
Both species gene heated to split
The individual strands are mixed and allowed to cool. Hydrogen bonds form between complementary nucleotides- hybridised DNA
Reheated and how much it is lower determines how different strands are- low separation temp suggests lots of difference and few hydrogen bonds and rise versa
how can dNA sequencing be used?
DNA hybridisation only provides a degree of overall difference
Modern DNA sequencing is more accurate
The exact number of nucleotide differences
what isa phylogenetic tree? what are the features?
Phylogenetic tree: branching diagrams that depict the evolutionary relationships between different groups of organisms.
Branch from common ancestors
Use homologous features- morphological and molecular
A hypothesis (most unknown)
Grouped with similar DNA and RNA
phylology
evolutionary history of linages as the diverge from a common ancestor over time.
Linnaean system of classification
organisms are organised into a hierarchy of groups (taxa) reflecting evolutionary relationships.
taxonomy
classifying based on shared characteristics and evolutionary relationships.
limitations of comparative morphology and classification?
Divergence of species may have species classified as distantly related
Convergence of species may have them classified as closely related
Now better techniques
