4.2. Evolution Flashcards
Define evolution. Define fitness.
Change of allele frequency of heritable traits in the gene pool of a population over time.
The survival and reproductive success defined by an organisms genetic information.
Lamarckism vs Darwinism
Lamarckism says that acquired traits are transferred from one generation to another, Darwinism that only heritable traits get transferred.
Explain the steps of evolution by means of natural selection.
- Overproduction of offspring – each couple tends to produce more offspring than the environment can support which increases the survival chance of the population and also increases variability
- Variation of traits in a population – individuals differ by their level of fitness (how well you can adapt to the environment because of your particular genes).
- Competition for resources – survival of the fittest, those with a genetical advantage survive because they are better adapted
- Better adapted individuals produce more offspring so their more beneficial traits/genes are more frequent in the successive generation and after several generations the allele frequency in the population changes
Types of selections. Types of selection pressures.
Natural, sexual and artificial.
Biotic or abiotic and density dependent or density independent
Explain sexual selection on the example of peacocks.
Male peacocks have larger tail feathers than it would be optimal based on their survival success (the ones with shorter tails are quicker so natural selection selects them) because female peacocks prefer longer tails because the peacocks that survive despite long tails must be the fittest and the strongest. Generally, males are chosen based on female preferences for male traits.
Sexual vs natural selection. Describe the experiment with guppies.
Sexual selection selects individuals based on their mating success while natural selection selects based on fitness/survival capabilities.
Biologist Jon Endler conducted an experiment with guppies. Female guppies prefer colourful males as mates; however, they are also more likely to be eaten by predators because they are easier to spot. Some parts of the streams where guppies live have less dangerous predators than others, and in these locations the males are more colourful and in locations where predators are more dangerous, they tend to be less colourful. Guppy population in each area has evolved in response to the competing preferences of females and predators present in a particular area.
Explain artificial selection.
Humans perform selective breeding with wild animals to produce their domesticated form (species). They favour animals with desirable traits and only allow those to reproduce so the desirable genes accumulate and after some time create a new species. This shows that artificial selection can cause evolution (e.g. pig and wild boar).
List and explain different types of evidence for evolution.
- Comparing sequences (a-a, DNA, RNA) – the more similar the two organisms are, the fewer differences in sequence there are.
- Homologous anatomical structures
- Selective breeding of domesticated animals and plants
Homologous vs analogous structures
Homologous structures – result of adoptive radiation (the same body part adapted to different habitats and functions so it looks different in different species originating from the same common ancestor) – e.g. Pentadactyl limb in vertebrates (except fish), forelimb
Analogous – result of convergent evolution (characteristics with separate origins (no common ancestor) but serve the same function – e.g. bat and bird wings (anatomical differences)
Define adaptive radiation.
Type of evolution from an ancestral species which changes some aspects of its appearance/behaviour to take advantage of new environmental opportunities. Common after cataclysmic events when new niches open for the surviving species.
Explain the process of gradual speciation.
- A population thrives on a common habitat – random mutations can be exchanged among members of the population (genes can flow) but individual organisms remain similar and members of the same species
- Introduction of a barrier which gradually separates common population into subpopulations – as the barrier grows, it becomes ever more difficult for them to interbreed so they become reproductively isolated
- Accumulation of different mutations without the possibility for their exchange among the members (no gene flow) + different selection pressure on different habitats leads to a change in allele frequency in the two separate gene pools
- Over generations, the reproductively isolated populations will evolve independently and lose the ability to reproduce with each other because their chromosome number will change or their chromosomes will become too different to pair up
List the types of reproductive barriers/isolations. Why are they important?
- Geographic (e.g. squirrels in Grand Canyon)
- Temporal – incompatible time frames that prevent populations or their gametes from encountering each other, populations interbreed during different times of the day, season, year…
- Behavioural – population’s lifestyle isn’t compatible with those of another population, courtship is unique to a species (e.g. male fireflies, bird song…)
- Isolation due to infertility caused by mutations – example of abrupt evolution – happens by polyploidy (e.g. genus Allium) an error in meiosis occurs and 2n gametes produce a 4n organism – polyploids can only self-fertilize or mate with another polyploid (reproductively isolated from the rest – 3n zygote cannot survive) – they usually grow larger most likely because of larger nucleus
Because they cause reproductive isolation which is the key for speciation.
Describe allopatric vs sympatric speciation.
Allopatric – reproductive isolation is geographical (assuming natural selection is different at two habitats) there is a divergence of the traits of a population (e.g. Darwin finches evolution).
Sympatric – reproductive isolation is behavioural or temporal (due to a biological reason like a mutation) (assuming natural selection is different at two habitats (because the populations are now reproductively isolated)) there is a divergence of the traits of population (e.g. apple maggot fly evolution)
Gene pool definition. Allele frequency definition. How does it change over time?
Consist of all the genes and their different alleles in an interbreeding population. The frequency of an allele as a proportion of all alleles of the gene in the population. p + q = 1 (p = frequency of the dominant allele). Allele frequency changes only if mutations, migrations or another mechanism of evolution happens.
State the Hardy-Weinberg principle and explain what it’s used for.
(p + q)^2 = 1
It describes the gene pool of a population, stating that allele and genotype frequency of a population won’t change despite sexual reproduction unless some of the mechanisms of evolution act upon that population.
