Origins of Biodiversity

Question 1

What is Evolution?

Answer 1

change in allele frequency in a population over time
- populations evolve individuals DO NOT

1. Locus - specific location of a gene / DNA sequence on a chromosome
   
   • monochromosome
   • does not necessarily code for a protein. A location.
2. Allele - variant of DNA sequence / locus
3. Population - a group of interbreeding individuals
   - localized group
   - changes allele frequencies so different populations are different
   - all populations combined is the species gene pool or metagene pool
4. Gene pool - total aggregate of alleles in a population
   - ** populations are different(florida is different than the middle east)
   - Populations are the unit not individuals

Question 2

How do populations evolve?

Answer 2

1. Migration
2. Mutation
3. Genetic Drift
4. Selection

Question 3

Mechanisms that cause allelic change:

Migration (aka gene flow)

Answer 3

a member of one population moves to another population and reproduces with a member of their population = change in allele frequencies

Question 4

Mechanisms that cause allelic change:

Mutation

Answer 4

alters allele frequency but also can add totally new alleles to the population

Question 5

Mechanisms that cause allelic change:

Genetic Drift

Answer 5

random change in allele frequency in a pop. over time

• random event does something to add or remove an allele from the population
• even meiosis and crossing over affect this
  
  • sampling bias
• natural disaster that is random in how it kills organisms
• all populations experience drift but as population gets smaller the effect of genetic drift greatens
  
  • **higher chance of a rare allele being totally removed from the population
  • no genetic capacity to survive future environmental change
• Bottle Neck Events – when a few alleles make it through an event and it drastically changes the allele frequency

Question 6

Mechanisms that cause allelic change:

Selection

Answer 6

a mechanism that shapes adaptations via differential reproductive success amongst different genotypes.

In other words, “if differences in replication rates exist between genotypes, then selection will skew genotype frequencies in favor of the one with the highest replication rate.

• For selection to operate, heritable variation in survival and reproductive success must exist. Selection is greatly enhanced when there is an overproduction of offspring.
• selection is the only thing that can shape adaptations

Question 7

How do we identify / study evolving populations?

Answer 7

1. Hardy-Weinberg equilibrium Theorem - allele / genotype frequencies remain constant from generation to generation unless acted on by one (or more) of the mechanisms of evolution
   a. In a single locus system with 2 alleles, p and q:
   1. p + q = 1
   b. To predict genotypic frequencies given an allele frequency:
   1. p2 + 2pq + q2 = 1
2. If a population’s observed genotypic frequency deviates from its predicted genotypic frequency, then the population is not in HW equilibrium (i.e. it is evolving)

Question 8

Where does genetic variation come from?

Answer 8

1. Mutation
2. Meiosis
3. Crossing Over
4. Random fertilization of gametes

Question 9

Genetic Variation:

Mutation

Answer 9

Substitution
- Silent, missense, and nonsense mutations

Insertion / deletion
- Causes frameshifts = very bad

Question 10

Genetic Variation:

Meiosis

Answer 10

Independent assortment = random gametes

Question 11

Genetic Variation:

Crossing Over

Answer 11

Creates recombinant chromosomes

Question 12

Genetic Variation:

Random fertilization of gametes

Answer 12

Another layer of randomness

Question 13

Where do new species come from (i.e. biodiversity)?

Answer 13

To achieve an increase in biodiversity, one needs three ingredients:

1. A new breeding population
2. Reduced gene flow between the new and original population
3. Time

These ingredients will lead to reproductive isolation.

Adaptive radiation - Rapid species diversification from a single common ancestor.
- Finches and Galapagos islands

Question 14

Adaptive Radiation

Answer 14

Rapid species diversification from a single common ancestor.
a. Finches and Galapagos islands

Question 15

New breeding population -> independent evolution -> reproductive isolation -> new species -> biodiversity

Answer 15

New breeding population -> independent evolution -> reproductive isolation -> new species -> biodiversity

Question 16

How is biodiversity created?

Answer 16

1. New breeding population
2. Reduced gene flow
3. Time

Question 17

These ingredients lead eventually to reproductive isolation.

But how does reproductive isolation evolve?

Answer 17

1. Pre-zygotic barriers
2. Postmating pre-zygotic(gametes passed but may not be successful) or (attempt to mate but fails in some capacity)
3. Post-zygotic barriers

Question 18

Pre-zygotic barriers(premating)

Answer 18

1. Habitat isolation
   
   • water vs land etc
2. Temporal Isolation
   
   • different time of year for reproductive cycles
3. Behavioral Isolation
   
   • partners don’t want to mate or have the right colors so they get ignored

Question 19

Post-zygotic barriers

Answer 19

1. Reduced hybrid viability
   
   • offspring made but weak and cant make it to adult hood
2. reduced hybrid fertility
   
   • offspring makes it to adulthood but is not fertile
3. hybrid breakdown
   
   • Offspring able to reproduce but when the hybrids reproduce with each other the next offspring is unstable
     o Larger portion of offspring have recessive alleles which become apparent and fail

Question 20

What is a species?(biological species concept)

Answer 20

A completely abstract concept with no specific answer

The biological species concept – species are groups of actually or potentially interbreeding natural populations that are reproductively isolated form other such groups.

Question 21

Patterns of speciation:

Allopatric versus sympatric

Answer 21

Allopatric – geographic separation restricts gene flow

  - Odds of speciation drastically increase when the speciating populations are both SMALL and ISOLATED.
 - river cuts off path for squirrels 

Sympatric – biological factors reduce gene flow

 - may result from polyploidy or mate / habitat preference
 - plants do this often
 - tetraploids

Question 22

Patterns of speciation:

Anagenesis versus cladogenesis

Answer 22

Anagensis – gradual transition from one species to another

 - always happens even if cladogenesis happens
- in gradualism

Cladogenesis – branching of one or more new species from a parent species

Question 23

The pace of evolution:

Gradualism

Answer 23

Gradualism – speciation occurs gradually over time

Gaps in fossil record prevents an accurate assessment of speciation rate in many lineages.

Why are there fossil gaps?

1. Wrong environment
2. Soft bodies
3. Episodic /local fossilization
4. Fossils lost

Question 24

The pace of evolution:

Punctuated equilibrium

Answer 24

suggests that gaps in fossil record not actually gaps. In short, PE states:

1. several populations of a species exist, one large and several small;
2. The large population is captured in the fossil record, the small populations are not
3. Natural selection is less effective in large populations. Thus, the large population is in stasis, but the small populations keep evolving.
4. At some point, one of the small populations evolves a superior adaptation (s) and outcompetes the other populations (AKA a selective sweep)
5. New superior population than grows large and enters evolutionary stasis due to its large size.

The above steps appear as if a species has undergone an abrupt evolutionary change, since these small populations are not fossilized.

Question 25

Why are there fossil gaps?

Answer 25

1. Wrong environment
2. Soft bodies
3. Episodic /local fossilization
4. Fossils lost

Question 26

Locus

Answer 26

specific location of a gene / DNA sequence on a chromosome

- monochromosome
- does not necessarily code for a protein.  A location.

Question 27

Allele

Answer 27

variant of DNA sequence / locus

Question 28

Population

Answer 28

a group of interbreeding individuals

• localized group
• changes allele frequencies so different populations are different
• all populations combined is the species gene pool or metagene pool

Question 29

Gene pool

Answer 29

total aggregate of alleles in a population

• ** populations are different(florida is different than the middle east)
• Populations are the unit not individuals

Question 30

Bottle Neck Events

Answer 30

when a few alleles make it through an event and it drastically changes the allele frequency

Question 31

Modes of selection

Answer 31

1. stabilizing
   
   • the outliers disappear and one very specific phenotype remains
2. disruptive
   
   • population splits into two distinct phenotypes
3. directional
   
   • a trait moves the phenotype to one direction.
   • think bird eats yellow beetles so beetles become darker over time

Question 32

adaptive evolution

Answer 32

Darwin figured this out
- traits that help individuals survive in the environment via natural selection tend to be passed on as other traits disappear from pool

Question 33

Sexual Selection

Answer 33

Sexual selection is a type of natural selection that refers to selection in direct relation to reproductive success.

• Sexual Selection – choice of mate(assortative mating) may push some traits out of gene pool(blue birds don’t like yellow but only 1 yellow bird around. Yellow doesn’t reproduce and yellow trait is gone)

Question 34

Pre-zygotic barriers(postmating)

Answer 34

Postmating pre-zygotic(gametes passed but may not be successful) or (attempt to mate but fails in some capacity)

1. mechanical isolation
   - the parts literally do not fit together right to work
2. gametic isolation
   • the receptors on the gametes don’t communicate correctly
   • sperm competition where sperm from other species loses in a literal battle

Question 35

Associated problems with BSC(Biological Species Concept) are that it doesn’t apply to:

Answer 35

1. Asexual organisms
   
   • Makes no sense to classify each individual organism as a specific species
2. Fossils
   
   • Fossils cant reproduce
3. Organisms that we know little of their reproduction