variation in populations

* means that you don't need to know it.

species

a group of similar organisms that can interbreed in nature and produce vigorous, fertile offspring

→ means that their offspring will survive to reproductive age and then produce offspring of their own that can also reproduce

subspecies

different races of the same species, who do not interbreed directly, but gene flow still exists

e.g. tigers: bengal, siberian, simatran

they can technically interbreed but they don’t really because their geographic location is different

extinction

the permanent loss of a species (*usually hasn’t been seen for 50 yrs or more).

if referring to small group, say extinction of population

population

a group of organisms of the same species living in a defined geographic region at the same time

e.g. wombats: population of northern hairy-nosed wombat

gene pool

the genetic makeup of a population; includes the sum of all the alleles for different genes present in a population

→ basically all of the alleles that are present for the different genes within that population makes up their gene pool

What is an allele?

a different variation of a gene. genes code for proteins, so we have somewhat different proteins produced in different individuals

gene flow

the movement of genes and alleles between populations.

gene flow increases the genetic diversity within a population

why is variation important?

important for a population to survive any sudden change in their environment

*variation occurs when members of a population display different phenotypes (traits)

e.g. *physiological, structural or behavioural traits.

sources of variation

• reproduction → passing alleles to offspring

• gene mutation/mutation in alleles

• environment causes phenotypic variation (e.g. tanning)

2. How can you measure genetic diversity?

by examining the gene pool of a population and calculating the allele frequency

What does it mean if a population has a wide range of alleles?

they are genetically diverse

For Hardy Weinberg what does P and q mean?

P - dominant allele

Q - recessive allele

genetic drift

the random changes in allele frequency due to chance events

What kind of population does genetic drift have a more pronounced effect in?

more pronounced effect in small populations, and this can result in the loss or fixation of an allele

• this results in reduced genetic diversity in small populations.

in this pic, blue is fixed and red is lost ☹

types of genetic drift/allele frequencies changing in a population

founder effect, bottleneck effect

the founder effect

occurs when a few individuals migrate to create a new population in a different geographic location that is not representative of the original population

allele combinations are different from original population AKA the individuals are genetically different to the og population, resulting in a different gene pool → *they will be very different genetically

since there are only a few founding individuals, there will be very low levels of genetic variation

*it’s basically the result of inbreeding?😟

the bottleneck effect

the severe reduction of individuals in a population generally due to a catastrophic event such as disease, bushfire, or human impact

population will increase in numbers over time, but genetic variation stays low as the gene pool only comes from surviving individuals

→ *inbreeding again 🤕

3. Fossil record

fossils appear in an order of ‘fossil succession’ from single cellular organisms to structurally complex multicellular organisms

several mass extinctions have occurred throughout Earth’s history

What opportunities do mass extinctions provide?

mass extinctions provide opportunities for other species to thrive and diversify

fossil

the remains of an organism or direct evidence of its presence on Earth

Is the fossil record complete, and why?

it is incomplete because:

• most organisms do not get fossilised due to the conditions required to do so

• or the fossils are too old so the DNA is degraded and scientists are unable to identify the organisms and where it fits in the fossil record

Where are most fossils found?

in sedimentary rock

How are fossils mostly formed?

through the process of mineralization, where

• hard body parts are replaced by hard minerals as the surrounding sediments turn into rock

Why do we not find fossils in igneous (volcanic) rock?

it’s probably too hot so they js die

conditions for fossilisation (RUD)

fossilisation is very rare, but when it does happen:

Rapid burial - covered in sediment; usually underwater

Organisms lies Undisturbed - no predators, no earthquakes, etc

Decomposition is prevented - Low O2, low temp, low moisture, to prevent bacterial decomposition

types of fossils

body, trace, index, transitional

body fossils

fossils of the actual organism

e.g. bones, teeth and claws

soft tissues such as skin, muscles, and organs are very rarely fossilised

trace fossils

not the actual organism. e.g. burrow, footprint, faeces

index fossils

a fossil that:

• had a wide geographic distribution

• existed for a relatively brief period of time

fossils that are found in the same rock layer can be estimated to be the same age.→ form of relative dating

transitional fossils

intermediate forms of organisms that provide an evolutionary link between species.

dating techniques

relative dating, absolute (radiometric) dating

relative dating

• the age of the rock is determined by comparing it to another rock

• stratigraphy/stratification:

  • the study of the sequence of rock layers (strata) in any one area

  • layers deposit over time

  • older layers are lower

uses index fossils → fossils in the same layer estimated about same age

⭐️ a fossil’s relative age is provided!

absolute (radiometric) dating

• provides a numerical (absolute) age for a fossil

• based on radioactive isotopes and their half-lives

• half life - the time taken for half of the parent isotope to decay into its daughter isotope

describe the difference between relative and absolute dating

relative:

• uses the Earth’s layers to determine whether one fossil is older than another based on the position in the rock layers. (older fossils lie deeper than younger fossils)

absolute:

• uses the decay of certain elements to calculate the actual age of a fossil. (half life = time taken for half of a sample of atoms to decay.

carbon dating

dating organic fossils that contain carbon. they must be less than 50,000 years old

4. selection of phenotypes

why are some individuals more likely to survive

some individuals are more likely to survive change in their envronment due to a particular phenotype

How does variation exist in the population?

through mutations that may have created new alleles or by different allele combinations in sexual reproduction.

Recall the process of Natural selection, what variation means for individuals in a species, and what the result of this is

variation exists in individuals within a species that may lead to an advantage if a change in the environment occurs

a selection pressure present in the environment acts on that variation

→ this means some individuals in the population have a survival and reproduction advantage

individuals that survive pass on the allele to the next generation through reproduction, resulting in more individuals with the trait.

→ this results in increased allele frequencies for the trait in the population

it acts on certain individuals in a population, not the whole population

selective breeding

a human (usually a farmer) selects the trait that is desired based on phenotype

• selects two organisms that display the trait, and breeds them → to increase the chance of offspring having these traits

• observes the offspring, and then selects the offspring with the best version of the desired trait. Breeds the offspring

completes the process many times until the trait is observed in all offspring

selection pressures *

• predators

• availability to resources (water, shelter, mating habitat)

• food sources

• disease/pathogenic spread

• environmental phenomena (natural disasters)

• weather conditions/changes (e.g. floods, storms, etc)

• abiotic conditions (e.g. temp, CO2 concentrations)