1st Biology Midterm

what is evolution also referred to as

macroevolution

evolution defintion

• change in the genetic composition (or heritable traits) of a population from generation to generation

• shows how we have acquired a diversity of new forms

• ALSO

  • change in the allele frequencies of a population from generation to generation

darwin saw that only a limited # of organisms actually survive and produce offspring (not that populations just grow in general)

descent with modification

• passing down characteristics/traits from one generation to another while undergoing some modification with time

• things change with descent

what type of traits are changing with evolution

• heritable traits

why is evolution only a theory

• it is supported by observations and experiments

• it can be refined if new evidence emerges

what does it mean when evolution is predictive

• based on this we know this will happen

how is natural selection related to evolution

• natural selection CAUSES evolution

artifical selection

• change in the genetic structure of populations due to selective breeding by humans

• humans change and mix and do things

homologous

• same evolutionary origin but differ now in structure and function

• can be anatomical, molecular

analogous

• similar function, different evolutionary origin

• ex. bat, bird, butterfly

genetic variation

• differences among individuals in the composition of their genes or their DNA sequences

  • but don’t ALWAYS lead to phenotypic differences

• originate in differences in genotype that result in different alleles and then differences in phenotype

species accumulate differences, as a result, descendants differ from their ancestors which basically means a new species arose from an existing one

Darwin and NS as the mechanism of evolution:

observed that heritable variations in organisms, combined with overproduction of offspring and limited resources, inevitably led to a "struggle for existence," where individuals with advantageous traits survived and reproduced more, passing those traits on, gradually changing populations over generations

evolution can result from…

ANY process that causes a change in the genetic composition of a population

what is REQUIRED for evolution to occur

genetic variation

• because if everything stays the same how can anything change?

population definition

• the same species in the same geographic area living at the same time

  • that interbreed

what were the observations that pre-date Darwin’s theory (and helped him too)

• the earth is old

• when populations get too large they don’t survive

• fossils were discovered

what do INDIVIDUALS experience and what do POPULATIONS experience

INDIVIDUALS: selection

POPULATIONS: evolution

Lamarck’s theory of inheritance

• organisms change due to environment

• traits that are used improve over time and are inherited by offspring

  • ex. a giraffe stretching his neck to reach the leaves will stay with that neck and pass it down

• triats that aren’t used disappear

  • good things stay, bad things leave

what did Lamarck say about using traits?

• if you use a trait it will make it better not worse

• using things is good and improves it

what do species move towards in Lamarck’s theory of inheritance

• they move towards complexity

  • they want to be better

    • ex. a bug wants to be a frog, a frog wants to be a human (and we are the best)

natural selection

• an increase in genotypes with higher fitness in an environment

Tenets (components) of natural selection

• many offspring are produced, not all survive

• traits vary among indvidiuals within a population and may be heritable

• some heritable traits give individuals an advantage in their environment

• advantageous traits confer higher fitness and therefore become more common

what makes natural selection different than artifical selection

• when NATURE drives the traits being more favorable or not

Darwin saw it is okay to lose offspring, resources are not unlimited

what did Darwin propose

• that species always had one thing and were static

• common ancestry

Lamarck saw that animals improve…

THEMSELVES (not their genes changing anything)

• we are actively changing our bodies but not true because you can’t WILL yourself to change

convergence

• similarity of form/function due to similar environments and NOT common ancestry

• they look the same but they really are distantly related

phenotypic plasticity

• a genotype that produces different phenotypes in reponse to the environment

• a single genotype can do this

• seasonal phenotypic plasticity

is the phenotype that results from plasticity heritable

• it is NOT so it CAN’T be evolution

conditions for natural selection

1. have to have variation

2. these variations have to be genetic

3. there must be a way that only certain populations are allowed to survive

when environmental conditions reverse so does selection pressure

what does natural selection do to homologous structures

• when there are homologous structures natural selection will modify them and choose what’s best and then evolution occurs

more on phenotypic plasticity and heritability

• the GENE of being phenotypically plastic can be inherited but not the phenotype itself

do all phenotypic differences indicated genetic variation? (ex. too)

• NO

  • in phenotypic plasticity they have different phenotypes but still the same gene

sources of genetic variation

• point mutations

• chromosmal mutations

• crossing over during meiosis

how many alleles are there on a locus? Describe them

• 2

  • dominant: determines phenotype

  • recessive: masked in phenotype

allele definition

• different variants of a gene

gene pool

• all copies of all alleles at every locus in all members of the population

Hardy-Weinberg Principle

If there are no evolutionary influences the allele frequencies and genotypic frequencies will remain the same

Assumptions of Hardy-Weinberg Equilibrium

1. no selection

2. no mutation

3. no immigration or emigration

4. a large population

5. random mating

• none of these because all individuals should have an equal likelihood of surviving and reproducing

what type of hypothesis is hardy-weinberg

• a NULL hypothesis

  • because it shows the frequencies of alleles and genotypes in the absence of evolution

    • and essentially a null hypothesis says that nothing is actually happening, which lines up with H-W

how do you tell if a population is in Hardy-Weinberg equilibrium?

• if the allele frequncies from the offspring match the parent

  • nothing should have changed

how to do hardy-weinberg

• can use parent allele frequncies to get genotype frequencies and use these to get offspring allele frequencies

how to calculate allele frequency

• # of copies of an allele in a population divided by the total # of all alleles for that gene

how to calculate phenotype frequency

• # of individual with the phenotype divided by the total # of individiuals in that population

what would we expect in the parents if an organism has phenotypic plasticity

• if an organism has phenotypic plasticity for a trait then we would predict similar phneotypes between parent and offspring when they live in similiar environments

  • because they would be changing in that environment

gene definition

• piece of DNA that codes for a specific trait

gene and allele relationship

• a gene codes for a specific trait and an allele is a variant of a gene

• gene = eye color

• allele = blue eyes, brown eyes

what is evolution looking for

• a change in allele frequency

what is probably happening if we aren’t in Hardy-Weinberg

• evolution

if we are in the real world what do we have to use to see if we really do have no difference and to see if we are in Hardy-Weinberg

• chi-square

mechanisms of evolution

1. mutations

2. gene flow

3. nonrandom mating

4. genetic drift

5. selection

   1. can be artifical or natural

gene flow

• when people are moving and sharing their genes

• injecting new genes into new populations

• share genes

genetic drift

• change in allele frequency due to chance

• has a larger effect on small populations

• can cause alleles to be fixed

bottleneck effect

• type of genetic drift

• large population rapidly becomes a small one because of a random event

• 
  

what is most likely to happen with the bottleneck effect

• fixation of a trait

founder effect

• type of genetic drift

• small # of individuals establish a new population

• the founder isn’t carrying all the alleles from its old home so some are lost

what has lower genetic diversity in regards to the founder effect

• the daughter populations have lower genetic diversity than source populations

intrasexual selection

• type of sexual selection

• selection within a sex to compete for mates

intersexual selection

• type of sexual selection

• MATE choice

• selection by one sex for mates

balancing selection

• when multiple forms of an allele are maintained and one doesn’t get fixed

• about maintiang different forms of an allele

when does balancing selection occur

• Heterzygote advantage

• negative frequency-dependent selection

heterzygote advantage

• when the heterzygotes have a greater fitness than either homozygotes

negative frequency-dependent selection

• the rarest model has a higher fitness

  • because the most common one keeps getting attacked

• fitness depends on how common the phenotype is in the population

• the name is meant to mean inverse (negative of the other)

constraints of evolution (what can limit NS from producing things)

• laws of physics, thermoydnamics, gravity

  • traits can’t violate these

• sources of genetic variation

  • can only use the variation that’s there

• adaptation is opportunistic

  • not just random traits and if its benenfiical it will be choosen

• trade-offs

  • improving one trait means the other is reduced

• environmental change

  • can’t predict the future environment

directional selection

• selection favors one beneficial triat and it shifts to that side

stabilizing selection

• selection favors the intermediates by making it more common and removing extremes

• distribution becomes narrower

  • the middle hump becomes narrower

disruptive selection

• selection acts to eliminate the intermediate phenotypes and favor the most extreme phenotypes

• 2 peaks

  • removes middle

why does genetic drift make a bigger impact on smaller populations?

• because there are less opportunities to control the randomness

how does genetic drift differ from natural selection? Include Dutch Settler example

• natural selection selects for BENEFICIAL triats

• Dutch settlers bringing in huntingtons disease is not favorable

assortative mating

• if they look alike will mate

• increases # of homozygotes

what does nonrandom mating do to genotype and allele frequencies

• changes genotype frequnecies NOT allele ones

  • because its not random so it is picking from the same alleles already there just rearranging them

biological species concept

• groups of actually (or potentially) interbreeding populations that are reproductively isolated from other groups

what makes it difficult to define a species

• local variation

  • some might be locally adapted in this way and can’t interbreed with others from elsewhere

• asexual reproducers

  • how do you go against the sexual part of the biological species concept

• hybrids

  • 2 defined species are able to interbreed

ecological isolation

• type of prezygotic reprodcutive isolation

• species mate in different places

• specific to animals in the same general vincitity

  • like one on the top of the mountain and the other at the bottom

temporal isolation

• type of prezygotic reprodcutive isolation

• species mate at different times

behavioral isolation

• type of prezygotic reprodcutive isolation

• unique behaviors attract different species

• have certain behaviors that is a unique thing that only species don’t do

• ex. different fireflies fire light at different frequencies which will differentiate them

mechanical isolation

• type of prezygotic reproductive isolation

• differences morphologically prevent mating

• physically different structures that might not connect during sex

gametic isolation

• type of prezygotic reprodcutive isolation

• sperm can’t fertilize eggs

• sperm can’t get to the egg

• reproductive structures are compatible but sperm and egg are not connecting

reduced hybrid viability

• type of postzygotic reproductive isolation

• hybrids don’t live to maturity

reduced hybrid fertility

• type of postzygotic reproductive isolation

• hybrid parents don’t produce viable offspring

  • so they can’t interbreed with their original one and become their own species

• they make a healthy baby but that baby can’t reproduce

hybrid breakdown

• type of postzygotic reproductive isolation

• the viability of a hybrid offspring reduces after several generations

• first hybrid generation is good, and then second gets worse

what does reproductive isolation do?

• it maintains species boundaries

hybridization definition

• when reproductive isolation between two species breaks down

reinforcement

• REINFORCE barriers

• when natural selection reinforces prezygotic isolating mechanism

  • so they don’t breed and make less fit hybrids

• when hybrids are LESS fit than the non-hybrid

• individuals that hybridize have fewer offspring

  • can have offspring but aren’t sutied for the environment and the parental is better and then a barrier rises

    • so reproductive isolation increases and natural selection tries to block this mating

fusion

• weakening reproductive isolation

• hybrids are MORE fit

• individuals that hybridize have an equal # or more offspring

• reproductive isolation decreases

• there is no selection against hybridization

• parental offspring will disappear and the hybrid will be more common

stability in terms of hybridization

• hybrids can be more fit if they are in a specific location/time (stabiltiy)

• hybridization limited

  • small hybrid zones or variable conditions

  • hybrid production continues

• 
  

what is the result of reproductive isolation

• speciation

what does gene flow do in terms of reproductive isolation

• REDUCES IT

  • and therefore reduces speciation

what evolutionary processes lead to reproductive isolation

• natural selection

• genetic drift

• mutation

describe allopatric speciation

• there is one species

• FIRST become geographically separated and then selection and drift lead to speciation

  • they are on these separate barriers, natural selection chooses their traits for them, and then eventually they become so different they aren’t one species anymore

sympatric speciation

• one species

• polymorphism appears

• and then assortative mating happens

  • and people only mate with those that they look like and speciation occurs

• 
  

what does prezygotic mean

• before fertifilization (before the sperm meets the egg)

postzygotic reproductive isolation

• still species boundaries but have met the egg

• have formed a hybrid

what do prezygotic barriers do

• They stop mating or fertilization from happening at all

• They prevent wasted energy and reduce the chance of producing unfit hybrids.

what do both prezygotic barriers and postzygotic barriers do

• Both barriers maintain separation between populations

• Both contribute to speciation

Prezygotic barriers prevent mating or fertilization from occurring, while postzygotic barriers prevent hybrid offspring from surviving or reproducing, and together they reduce gene flow and promote speciation.

sterile defintion

• unable to produce offspring

hybrid zone

• where a hybrid is more fit