Evolution Flashcards
What is evolution?
The change in the properties of groups of organisms over the course of generations that is transmitted via genetic material from one generation to the next
What is essentialism? - Plato and Aristotle.
Essence as a transcendent ideal form, variation is accidental imperfection.
What is special creation?
Christian philosophy where each species has been created individually by God in the same form as today.
What did Galen do?
Dissected human corpses to study human anatomy. Previously knowledge was based on animal dissections.
Contributors to historical knowledge:
Comparative anatomy (Galen). Observation. Fossils - old earth, ancient life. Linnaeus - nested hierarchies rather than scala naturae. Lamarck. Uniformitarianism. Ecology of humans - geometric human growth + arithmetic food growth = crisis point = selection pressure. Natural selection.
Lamarckian evolution:
Species change over time driven by use and inheritance. Evolution from simplicity to complexity.
Species originated individually by spontaneous generation. Hierarchy as species originated at different times and differ in age.
What is uniformitarianism?
Lyell, Hutton - the same processes operated in the past as today. Geology should be explained by causes that can be observed today.
When was the HMS Beagle’s voyage?
27.12.1831 - 2.10.1836.
Visited Africa, South America, Australia and more.
What are Darwin’s finches?
Finches from different islands form 13 closely related species. Beaks adapted for different food sources on the islands. Darwin suggested they were once one species.
Evolutionary theory: Darwin and Wallace.
- The characteristics of organisms change over time.
- Species have diverged from a common ancestor - life is all one family tree (common descent).
- Differences between organisms evolved incrementally (gradualism).
- Evolution occurs by changes in the proportions of individuals in a population with different inherited characteristics (population change).
- Changes in proportions are caused by differences in the individuals’ abilities to survive and reproduce - adaptations (natural selection).
Differences between Darwin and Lamarck:
Darwin: Common ancestry. Based on random variation. Evolution towards better fitness and survival. Extinction. Lamarck: No common ancestry. Depends on use vs disuse of traits. Evolution towards increased complexity. No extinction.
Darwin and Wallace did not explain hereditary variation. What was the prevailing theory?
Blending inheritance - parents characteristics are mixed and offspring are intermediates between their parents features. Reduces variation.
What did Mendel do?
Discovered particulate inheritance by hybridising peas. Discrete genes, dominant and recessive. Characteristics inherited as particles which are unchanged from one generation to the next. Variation continues.
What is a species?
A group of individuals that reproduce primarily among themselves.
What is the modern synthesis?
Reconciled Darwin’s theory of natural selection with genetics. Acquired characteristics are not inherited (except epigenetics), variation is amplified by recombination, evolutionary change entails a change in proportions of individuals in a population with different genotypes by random drift/natural selection. Speciation.
What causes adaptive evolution?
Mutation and natural selection.
What is speciation?
The origin of 2 or more species from a single common ancestor which usually occurs by the genetic differentiation of geographically segregated populations.
How old is the Earth?
4.5 billion years old based on radiometric dating (1/2 life = 0.7 billion years).
How does most of the evolution of DNA sequences occur?
By genetic drift (rather than natural selection). Molecular clock.
What are small, medium and large mutations?
Small: nucleotide sized.
Medium: sub-chromosome sized.
Large: chromosome and karyotype sized.
What are the ultimate sources of variation?
Mutation and recombination.
What is genetic variation?
Differences in the genetic sequence inherited.
What is environmental variation?
Differences in the environment of an individual.
What is developmental noise?
Random events at the molecular level.
What are the sources of variation in phenotypic character?
Genetic variation, environmental variation and developmental noise.
How does the environment affect development or expression of features?
Enzyme induction, environmental sex determination and maternal effects.
What are small mutations?
Point mutations (may cause new protein sequences), insertions and deletions (frameshifts - often produce non-functional proteins).
What are medium mutations?
Inversions and horizontal gene transfer (foreign DNA, entirely novel functions).
What are large mutations?
Translocations - exchange of segments from non-homologous chromosomes, may be balanced (euploid) or unbalanced (aneuploid), metacentric/acrocentric chromosomes.
Karyoptic changes - polyploidisation in plants).
What is the problem with polyploidisation in plants?
Barrier to gene flow and speciation. 15-30% of speciation accompanied by ploidy increase in vascular plants.
When do mutations mostly occur?
During DNA replication in cell division. Some changes are not repaired by DNA polymerase and proof reading enzymes.
Why do mutations in somatic cells have no evolutionary consequences?
They are not transmitted to the next generation (in organisms where the germ line is segregated from the soma in early development).
How is the rate of a mutation measured?
The number of independent origins per gene copy per generation.
What is the average mutation rate as measured by the patience method (waiting for mutations to occur at specific loci)?
10^-5 to 10^-6 mutations per gamete per generation.
What is the indirect method of estimating mutation rate?
Comparing the number of base pair differences between homologous genes of different species with the time since they diverged (known from fossils). 10^-9 per sexual generation (eukaryotes).
What is the direct method of estimating mutation rate?
Next generation sequencing.
How many base pairs are in the human genome?
7x10^9.
Are mutation rates constant?
No, they vary between genes and chromosome regions. They are also affected by mutagens.
Mutations occur at random but:
- All mutations are not equally likely (developmental constraints).
- All loci are not equally mutable (differences in rates).
- Environmental factors influence mutation rates.
Why is mutation not equivalent to evolution?
Most mutations do not become fixed (substitutions) - where the mutation is carried by nearly the whole population due to natural selection or genetic drift.
How does recombination contribute to variation?
Reciprocal recombination does not generate new alleles, but creates new combinations of alleles at different loci.
Non reciprocal recombinations cause tandem duplications. Subsequent mutations can then lead to new proteins.