BIOL1400 4th Exam

Evolution=

central theme of Biology

Explains unity(shared DNA, metabolism) and diversity (species variety)

Darwin’s key ideas

decent with modification, natural selection

evidence for evolution

fossils, direct observation of natural selection, experiments, DNA comparisons

Basis of evolution

Darwin: natural selection drives evolution

Mendell: discovered inheritance patterns → explained how traits are passed from parents to offspring.

Genetic differences provide the raw material of evolution

Genetic variation

Phenotypic, genotypic, Polygenetic, single gene traits

mutations

creates new alleles, source of genetic variation, only mutations in gametes impact evolution

sexual reproduction

creates most genetic variation, crossing over, independent orientation, random fertilization

gene pool

all copies of every allele in a population

Darwin’s observations

variation among individuals in populations, heritability, populations produce more offspring than can survive and resources allow

natural selection

differential survival and reproduction based on heritable traits (non-random)

evidence of natural selection

Galapagos finches: Dry years → large seeds → bigger beaks survive → average beak depth increases

Pesticide resistance

Head lice resistance

microevolution

change in allele frequencies in a population over generations

Natural selection, genetic drift, gene flow

Genetic drift

random changes in allele frequencies stronger in smaller populations

bottleneck effect

founder effect

bottleneck effect

drastic reduction in population

founder effect

new population started by few individuals

gene flow

movement of alleles between populations through migration/gametes, reduces differences between populations

adaptive evolution

better fit between organisms and their environment

relative fittness

number of fertile offspring an individual produces relative to others. Fittest individuals are those that contribute most genes to the next generation

Natural selection alters variations

natural selection acts on phenotypes

Directional

Stabilizing

Disruptive

Directional selection

favors one extreme phenotype

Stabilizing selections

favors intermediate phenotypes

Disruptive selection

favors both extreme phenotypes

Sexual selection

form of natural selection where certain traits increase mating success

Intrasexual

Intersexual/mate choice

Intrasexual selection

competition for mates

Intersexual/mate choice selection

females pick based on best looks → good genes

sexual dimorphism

noticeable difference in appearance/size between sexes: males are showier

Evolution of Drug-resistant microorganisms

antibiotic resistance develops if misused

if you miss a dose, it gives the microorganisms a chance to adapt and become resistant to the drug

natural selection in microbes

random mutations generate variants, nonrandom selection favors survival of resistant strains, evolution is continuous and dynamic, making it challenging to eradicate disease

Why organisms are imperfect

selection can only act on existing variation, historical constraints, adaptations are compromises, interaction of chance(storms), natural selection(small population) and environment(unpredictable)

Why HIV evolves quickley

high mutation rate during replication (reverse transcriptase lacks proof reading) viral variants some resistance to drugs due to mutations

Due to rapid evolution, making an HIV vaccine is very difficult

Viral replication cycles

Lytic cycle- destroys host cell

Lysogenic cycle- doesn’t immediately destroy host

membranous envelopes with glycoprotein spikes

animal viruses, help entry/exit from host cells, DNA/RNA

Plant viruses

most RNA viruses, spread through plasmodesmata and vectors (insects)

Emerging viruses

new/rapidly spreading viruses

How viruses emerge

mutations, cross-species transmission, isolated populations

Retrovirus

HIV, RNA virus that makes DNA via reverse transcription

Explain why heritable differences in organisms’ phenotypes must be due to genetic differences. Why aren’t all phenotypic differences heritable? Give an example of a phenotypic difference that is heritable and one that is not heritable

Heritable traits come from genes passed to offspring. Some traits come from the environment only. Examples: Heritable- Eye color; Not heritable- muscle size from exercise.

If all the individuals in a population had identical genotypes, could the population evolve? If not, why not? If so, how?

If all genotypes are identical -> no evolution by selection (no variation)

Population could evolve later if new mutations or gene flow occur

Explain why an individual (e.g. you) CANNOT evolve.

Evolution = change in allele frequencies in a population over generations

An individual's genes don’t change - only populations evolve

Your friend tells you that polar bears evolved to have thick fur because it was necessary for them to survive in cold temperatures. Correct your friend’s misunderstanding.

Polar bears didn’t evolve thick fur because they needed it

Bears with naturally thicker fur survived better, passed on genes

Evolution acts on existing variation, not need or effort

Give at least two reasons that evolution cannot lead to organisms that are perfectly suited for their environment. Use hypothetical (or real) examples to illustrate your reasons

Trade offs- a trait helping one function can harm another

Changing environments- perfect today may fail tomorrow

Evolution = good enough, not perfect

Explain why mutations are important in the context of evolution even though they rarely cause significant changes in allele frequencies.

Mutations= sources of new alleles

Most have little effect, but without them, no new variation -> no evolution

Which mechanism(s) of microevolution, if any, would be likely to increase genetic diversity (variation) in a population? Decrease genetic diversity? Explain your reasoning

Mechanism	Effect on Diversity	Why
Mutation	↑ Increases	Creates new alleles
Gene flow	↑ Increases	Adds alleles from other populations
Genetic drift	↓ Decreases	Random allele loss
Natural selection	↑ or ↓	Depends on type of selection
Nonrandom mating	↓	Reduces heterozygosity

Which of the following statements about evolution is true?

Evolutionary change can increase the frequency of a harmful trait in a population.

Evolutionary change CANNOT lead to organisms that are perfectly suited for their environment. Which of the following correctly explain(s) why?

A trait that is beneficial in some ways can decrease an organism’s ability to survive and reproduce in other ways.

Environmental conditions can change.

Genetic variation arises randomly in a population.

ALL OF THE ABOVE!!!!

Which of the following, if any, correctly describes evolution?

A. Both individuals and populations can undergo evolutionary change.

B. Natural selection leads to organisms with the ideal set of traits to survive and reproduce in their current environment.

C. Some mechanisms of evolutionary change can introduce new alleles into a population in order to generate specific traits.

D. A population’s allele frequencies can only be altered by one mechanism of microevolutionary change at any given time.

E. NONE OF THE ABOVE!!!

The goal of the analysis was to test the hypothesis that genetic drift leads to decreased genetic variation in small populations (16 flies). What would be an appropriate control group ?

Populations of flies that start with 50% of each allele and are kept at 100 individuals each generation.

Explain why/how genetic drift influences the allele frequencies of all populations at all times

Random fluctuations in the frequency of alleles from one generation to the next. This process is driven by chance and can lead to the loss of genetic variation, the fixation of certain alleles, or the emergence of new traits. Key words/phrases: Random sampling, founder effect, bottleneck effect, inheritance, and small population size.

Explain why the allele frequencies of smaller populations are more likely to be significantly altered by genetic drift vs. the allele frequencies of larger populations.

The limited gene pool of small populations makes random fluctuations more likely to occur and persist. Over time, certain gene variants may become fixed in the population, meaning they are present in every individual, while others may be lost. Key words/phrases: loss of genetic diversity, vulnerable, reduced adaptive potential, susceptible.