Evolution

Question 1

Darwinism
What were Charles Darwin’s observations?
What was his theory?

Answer 1

Observations:
- Genetic variability = organisms of the same species are all different
- characteristics are inherited by offspring

Theory:
- Natural Selection: organisms that are better suited to an environment will increase in numbers, because they will survive & produce a greater number of offspring with good traits
- all organisms descended from a common anscestor

Question 2

Lamarckism
What was Jean Baptiste Lamarck’s theory?

Answer 2

Theory (incorrect):
- inheritance of acquired characteristics: an organism changs during its lifetime in order to be better adapted to its environment, and these changes are then passed on to its offspring
–> e.g.: giraffes stretch their necks to reach food, and then the offspring will be born with a longer neck than its parent

• Law of use and disuse of organs/ body parts:
  –> ogans/ body parts that are used a lot willl become larger & stronger
  –> organs/ body parts that aren’t used deteriorate & offspring wll eventually be born without it
  (CONNECTION TO EPIGENETICS)

Question 3

What do Lamarck & Darwin both agree on?
How does this contrast with creationism?

Answer 3

• all organisms are related
• life has changed and is still changing gradually over time
• populations change to be better suited/adapted to their environments
• life evolved from fewer, simpler organisms to many, more complex organisms

–> disagree with creationism!!

Question 4

What is Neo-Darwinism?
(aka synthetic theory)

Answer 4

= the modern view on evolution incorporating new scientific evidence and modern biological knowledeg
- genetics
- molecular biology of DNA & proteins
–> provide evidence to explain the molecular basis of variation, which is partially due to mutations, & mechanisms of evoltuion

Question 5

Darwinism:
What are the 4 main observations about populations from which Darwin derived the concept of natural selection?

Answer 5

1. Variation: charcteristics vary individuals (some of which are better adapted than others), leading to different rates of survival & reproduction
2. Selection: organisms that are kess adapted to the environment begin to die off
3. Survival/ heredity: organisms with preferred/ beneficial traits survive and pass those beneficial traits to their offspring
4. Reproduction (excess production): surviving individuals reproduce & pass on traits
   –> more offspring are produced than needed to replace parents and increase chance of survival

Question 6

What influences genetic variation within a species?

Answer 6

• mutations & gene duplications: produce new alleles and new genes
• size of the population & lifespan of individuals: mutations spread quickly in small populations & in organisms with short lifespans
• sexual reproduction
  –> gametes from 2 organisms with different genomes
  –> existing genes are arranged in new ways = recombination
  –> crossing over, random assortment, fertilization

Question 7

How is variability quantified?

Answer 7

as the average % of heterozygous loci
–> more heterozygous = more variation
–> more homozygous = less heterzygous = less variation

Question 8

What does phenotypic variation result from?

Answer 8

• inherited genotype
• envrionmental influence (sun exposure, diet, lifestyle, exercise…)

Question 9

What is microevolution?

Answer 9

= a change in allele frequency in a population over generations
–> evolution defined on its smallest scale

Question 10

What are 3 main mechanisms that cause changes in allele frequency in a population?

Answer 10

• genetic drift: chance events
• gene flow: transfer between populations
• natural selection: survival of the fittest

Question 11

What allows evoltuion to take place?

Answer 11

• a large genetic variation within populations
• natural selection NOT changes within an individual’s lifetime

Question 12

What are 4 contraints of natural selection? (how is it not always the ideal mode of evolution?)

Answer 12

1. Selection can only act on existing variations
   –> there may be even more ideal traits but they can’t arise on their own
2. evolution is limited by what traits an organism already has
3. adaptations are often compromises
4. chance events dont necessarily affect those best suited & rapid changes in the environment can limit the ability for an organism to adapt

Question 13

What are the 3 modes of selection (natural selection)?
In what situations do they happen?

Answer 13

directional selection: (peak at left side –> then later at right side)
- occurs when conditions favour individuals with 1 extreme of a phenotypic range
- common when an environment changes/ or part of a population migrate
- EXAMPLE: increase in large seed abundance –> individuals with large beak depth favoured and become more popular

Disruptive selection: (peak in the middle –> 2 peaks at either side with dip in the middle)
- occurs when conditions favour individuals at both extremes over individuals with intermediate phenotypes
- EXAMPLE: finches with soft/ hard beaks can easily feed on soft/ hard seeds –> finches with intermediate are inefficient at both

Stabilising selection: (wider curve with peak in middle –> slim curve concentrated in middle)
- acts against both extremes and favours/ maintains allele frequency for intermediate phenotypes
- reduces variation
- EXAMPLE: baby birth weight –> very large/ small babies have higher rates of mortality

Question 14

How does gene flow affect human populations (especially in present day)?

Answer 14

Has become increasingly important
- people move very freely now, travelling = easier to occur
- mating between populations is much more common now

As a consequence, there are fewer genetic differences between populations, due to exchange of alleles

Question 15

What is gene flow?

Answer 15

= the transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes (plants: pollen flies in wind or through bees)

Question 16

What are the effects of gene flow?

Answer 16

• reduces genetic differences between populations
  –> can even result in 2 populations combining into 1 with a common gene pool
• can effect how well populations are adapted to local environmental conditions (-ve)
• can also transfer alleles that improve ability to adapt to local conditions (+ve)

Question 17

What is the bottleneck effect?
What are the consequences?

Answer 17

= a sudden change in the environment, a chance event, that drastically reduces the size of a population and the genetic variability in that reduced population
= gentic drift

consequences:
- reduces genetic variability in the population, which could leave the population more vulnerable
–> some alleles may be over/underrepresented or even absent (wiped out)

in animals: often a result of human causes

Question 18

What is the founder effect?
How could it occur?

Answer 18

= when few individuals become isolated from a larger population & may establish a new population with a gene pool different to that of the original population
= a type of genetic drift

• could occur through a storm (causes birds or seeds to fly elsewhere), or migration to an island –> isolated
• humans: could occur when humans migrate somewhere isolated due to war or unrest??

EXAMPLE:
Amish community: polydactyly is present (condition in which a baby is born with 1 or more extra fingers)

Question 19

What is genetic drift?
examples

Answer 19

= the frequency of allels are affected by chance events

examples of chance events:
- a large storm
- chance events (e.g. mutations) during fertilisations
- environmental changes/ natural disasters

–> founder effect
–> bottleneck effect

Question 20

What are the consequences of genetic drift?

Answer 20

• large impact on genetic variation in small populations
• can cause allele frequencies to randomly change/ fluctuate –> unpredictable
• can lead to a loss of genetic variation within a population
• can cause garmful alleles to potantially be fixed within a populations (like amish community)
  –> threatens he survival of the population

Question 21

Which mechanisms of evolution benfit the species/ population?

Answer 21

natural selection:
- only mechanism that consistently improves how well organisms are adapted to their environments
- consistently enhances chances of survival and reproduction

genetic drift 6 gene flow may do this but only by chance

Question 22

What is the definition of a species?

Answer 22

= a group of populations whose members can interbreed in nature and produce viable, fertile offspring
–> members of a species are reproductively compatible

Different species are divided by:
- morphology (body form)
- physiology
- biochemistry
- DNA sequencing
–> dont produce viable fertile offspring when interbreeding with members of another species

Question 23

What holds the gene pool of a species together?
What is essential for the formation of new species

Answer 23

Gene flow: ongoing exchange of alleles tends to keep the different populations genetically similar

Reproductive barriers & reproductive isolation: essential to the formatio of new species

Question 25

What are reproductive barriers?

Answer 25

= biological factors that prevent members of 2 species from succesfull (or any) interbreeding

Question 26

What are different forms of isolation of populations/ reproductive barriers?

Answer 26

PREZYGOTIC BARRIERS (prevent mating/fertilization) - **habitat isolation:** despite same area - **temporal isolation:** different breeding/ mating times - **behavioral isolation:** different courtship rituals - **mechanical isolation:** mating attempted but not successful - **gametic isolation:** mating successful but fertilization unsuccessful POSTZYGOTIC BARRIERS (mating successful, but prevent successful development of hybrid/ zygote of 2 species) - reduced hybrid **viability**: hindered development - reduced hybrid **fertility**: may be sterile (e.g. mules) - hybrid breakdown: 1st generation could be successful, but then 2nd gen. won't be

Question 27

What is allopatric speciation?

Answer 27

= speciation with geographic isolation --> depends on the organisms ability to move --> the gene flow within the populations is interrupted

Question 28

What is the process/the steps of allopatric speciation?

Answer 28

1. geographic isolation --> populations are separated 2. separated gene pools change --> mutations, genetic drift, natural selection in different environments... 3. potential reproductive isolation between the 2 populations --> essentially 2 species now

Question 30

What is speciation? What are the different types of speciation?

Answer 30

= the process by which 1 species splits into 2 species --> enables the diversity of life --> helps explain many shared features between organisms **1. allopatric speciation:** = geographic isolation **2. sympatric speciation:** = occurs in a population living in the same geographic area - can occur if gene flow is reduced by: --> polyploidy --> sexual selection --> ressource (diet) differentiation --> habitat differentiation

Question 31

Examples the 3 modes of natural selection

Answer 31

directional: - timing of migration of sockeye salmon - increase in large seeds --> increase in beak size disruptive: - fur colour to camouflage - number of spikes on a cacti --> ppl take those with a perfect number stabilising: - human bruth size and weight - clutch size - siberian husky leg muscles --> strong but not too heavy

Question 32

What is sexual selection? + different types + consequences

Answer 32

= individuals with certain inherited characteristics are more likely than others to obtain mates **intrasexual:** individuals of same sex compete for male of opposite sex (e.g. stronger stags with pointier antlers win) **intersexual:** individuals of 1 sex are choosy in selecting their mates (e.g. females choosing birds with brightest colours, or humans of best health) --> can be -ve: bright colours = risk --> can be +ve: good health Can result in sexual dimorphism

Question 33

What is balancing selection? + different types

Answer 33

= maintains 2 or more types of phenotypes in a population --> oscillates over time **1) Frequency-dependent selection**: the fitness of a phenotype depends on how common it is **2) Heterozygote advantage:** heterozygote individuals have greater fitness than homozygotes