Exam 2 - Natural Selection and Speciation

What is a gene pool?

Gene pool is all of the genetic information like the different genes and alleles within a population

How do different evolutionary mechanisms influence the composition of a gene pool?

Natural selection, genetic drift, gene flow, and mutation all change allele frequencies in a population, which alters the gene pool over time

How do the gene pool of an evolving population compare to the gene pool of a non-evolving population?

In a non-evolving population the allele and genotype frequencies do not change over time and evolution does not occur → Hardy Weinberg assumption
In an evolving population the allele and genotype frequencies do change over time and lead to evolution

How do new species arise, and how can we recognize them?

When there is a geographical barrier a species is not able to reproduce with others from the other side of the barrier and this will eventually lead to differences within those populations
Over time this creates a reproductive barrier where organisms are not able to interbreed → if they cannot interbreed then they are considered different species

What is a species?

A species is a group of organisms that share genetic and morphological similarities and are able to reproduce with each other and not with other species

An example is the eastern meadowlark and western meadowlark because although they look similar they have different songs and behaviors which creates a reproductive barrier

What is a speciation event?

A speciation event is when new distinct species form due to reproductive isolation that prevents gene flow between populations
This can be caused by geographic barriers

When speciation occurs it splits one species into two and they share a common ancestor

How does microevolution differ from speciation?

Microevolution is changes in allele frequencies from one generation to the next and does not create a new species
Speciation involves enough change to create a new species and takes much longer

Microevolution is adaptation within a species; speciation is the creation of new species

How does reproductive isolation affect gene flow and the production of offspring?

If there is a reproductive barrier then organisms are less likely to reproduce → decreases gene flow and can lead to new species
If they do reproduce they may produce a hybrid organism which may be sterile (alive but cannot reproduce)

Are species fixed and stable at all times?

No, species are dynamic and change due to natural selection, mutation, and environmental pressures

Example: polar bears and grizzly bears can produce hybrid offspring (some are viable and fertile) due to overlapping ranges from climate change

Can the biological species concept be applied to asexual organisms or fossils?

The biological species concept does not work for asexual organisms or fossils because it requires evidence of interbreeding

What is the morphological species concept?

Defines species based on observable physical traits and can be used for asexual organisms and fossils

What is the ecological species concept?

Defines species based on ecological niche and adaptations to a specific environment

What is the phylogenetic species concept?

Defines species as the smallest group that shares a common ancestor and forms one branch on the tree of life

What is the biological species concept?

Defines species based on reproductive isolation and ability to interbreed

What are the two types of reproductive barriers that keep species separate?

pre-zygotic barriers
post-zygotic barriers

What are types of pre-zygotic barriers?

Zygote is not formed yet
Habitat isolation – live in different environments
Temporal isolation – mate at different times
Behavioral isolation – different mating behaviors (ex: meadowlarks)
Mechanical isolation – incompatible reproductive structures
Gametic isolation – sperm and egg meet but cannot fuse

What are types of post-zygotic barriers?

Reduced hybrid viability – offspring does not develop properly
Reduced hybrid fertility – offspring is sterile
Hybrid breakdown – first generation is viable but later generations are weak or sterile

What is the time frame for formation of new species and how do new traits arise?

New species form through speciation due to reproductive isolation and can take thousands to millions of years
New traits arise from mutations, sexual reproduction, and environmental pressures

What is allopatric speciation?

Allopatric speciation is the formation of new species due to geographic isolation where a physical barrier (mountains, rivers) splits a population and limits gene flow
The groups evolve independently and eventually cannot reproduce even if reunited

What is sympatric speciation?

Sympatric speciation is the formation of new species in the same geographic location without physical barriers
Reproductive isolation occurs due to factors like niches/resource use, mate choice, or genetic changes

What causes changes in allele frequency?

Natural selection, genetic drift, gene flow, and mutation

What is gene flow?

Gene flow is the transfer of alleles between populations due to migration
This increases genetic diversity

Urbanization can reduce gene flow by creating barriers, leading to inbreeding

What is genetic drift?

Genetic drift is RANDOM change in allele frequencies, especially in small populations
It can reduce genetic diversity

Types: bottleneck effect and founder effect

What is the founder’s effect?

When a small group leaves a population and forms a new one, carrying only some alleles → reduced genetic diversity

What is the bottleneck effect?

When a population is drastically reduced due to events like disasters → reduced genetic diversity

Which mechanisms lead to adaptation and which are not adaptive?

Adaptive – natural selection
Nonadaptive – mutation, genetic drift (founder and bottleneck), gene flow (random changes, not based on fitness)

What is inbreeding depression?

When closely related individuals reproduce leading to harmful recessive alleles being expressed
Causes reduced fitness, malformations, and lower reproduction

Urbanization increases inbreeding by limiting gene flow between populations

The Hardy Weinberg equilibrium equation measures what?

Measures allele and genotype frequencies in a population

What are the five necessary conditions of the Hardy Weinberg equilibrium?

No mutation
No natural selection
Large population (no genetic drift)
No gene flow
Random mating

Table for type of evolution, adaptive or not, increase or decrease in genetic diversity: