Biodiversity, Phylogenetic Trees and Evolution Flashcards
what is Evolution
Genetic change over time within a population
What are the three things Evolution requires
Variation
selection
heritability
What is Variation
Rise from genes or the environment both of which affect the development
What is Selection
Individuals survive bettwe or have more offspring based on their characteristics
What is Heritability
The correlation between parents and offspring ( how well the trait is transmitted) is the percentage of variation in a population explained by genetic variation.
What is heritable variation
It is based on differences in the DNA that affect the function or gene expression of proteins
Trees can be constructed Using
- morphology ( differences in body characteristics)
- differences in proteins, amino acids, or DNA
Phylogenies can be used to test
To time divergence ( meaning that trees can help estimate when two species’ genetic lineages split from a common ancestor)
Phylogenies can be used to test
hypothesis
I.e relationship between mitochondria and chloroplast
Phylogenies can be used to test
test convergence in morphology. traits
What are the important assumptions of phylogeneis
Change in DNA sequence occur at a steady rate over time, forming a molecular clock
what are the cons of phylogenies
Revisions result in underestimate
The clock depends upon a gene
What are some examples of reversions
- Masking true changes
- Multiple hits at a site
- saturation effect
What is masking true change
If a site mutates from an original state (A) to a derived state (B) and
then back to (A), the net observed change is zero. However, in reality, two mutation events have
occurred.
Multiple hits at a site
In rapidly evolving regions, multiple mutations at the same site can
obscure the true number of changes, leading to an apparent slowdown in the mutation rate.
saturation effect
Over long evolutionary timescales, sites may undergo multiple substitutions,
with some reverting to earlier states, making the number of observed differences between
species lower than the actual number of mutations.
What are some examples of clock depending upon a gene affecting phlogey
- Variation in Mutation Rates Across Genes
- Selection Bias
- Reversions and Saturation Effects
-Horizontal Gene Transfer (HGT) Issues
-Uneven Clock Calibration
Variation in mutation
Different genes evolve at different rates due to factors like selection pressure and functional constraints.
Highly conserved genes (e.g., RNA genes) mutate very slowly, whereas non-essential genes may evolve rapidly.
A single gene may not represent the overall evolutionary rate of an organism.
Selection Bias
Some genes experience strong natural selection, which can accelerate or decelerate mutation
rates.
If the chosen gene is under positive selection (e.g., immune system genes), it may evolve faster
than neutral regions, leading to overestimation of divergence times.
Converselv, purifvina selection slows mutation rates. leading to underestimation.
Horizontal Gene Transfer (HGT) Issues
when an organism gets DNA from another organism that is not its parent. Instead of passing genes only from parent to offspring (which is vertical gene transfer), HGT allows genes to jump between different species.
what characteristics should a tree have that will help us construct a phylogeny based off of DNA or amino acid?
- Has to be common to all organisms
- has to have the same function in all organisms.
- Mutations have to have accumulated at a steady rate over the entire 350 million years.
- There have to be areas of the sequence where mutations accumulate slowly and other areas where they accumulate more quickly so we can discriminate between animal groups that diverged more recently.
- Have to have maximum parsimony
Why do DNA and amino acids have to have the same function?
change in function would lead to fast changes due to natural selection that would not be related to time since divergence
What are neutral mutations in DNA
Molecular phylogenies are constructed using neutral mutations
Mutations happen at a steady rate and in a random genome sequence.
How is the molecular clock calibrated
The molecular clock is calibrated by dating fossils. This allows you to determine the
rate of change over time (# of neutral substitution per unit of time)
