P1 Natural selection and genetic modification

Who were two very influential scientists who explained evolution and natural selection?

Charles Darwin

Alfred Wallace

Charles Darwin background

- Spent 5 years on a voyage around the world

- He studied plants and animals at all the different locations

what did charles darwin notice on his voyage?

- noticed that there was variation in members of the same species in different locations

- the individuals who had characteristics most suited to their environment were more likely to survive, reproduce, and therefore pass on their characteristics

what did darwin's studies lead him to develop

to explain his observations, darwin developed his theory of evolution by natural selection

Alfred Wallace background?

- independently developed his own theory of evolution, based on the process of natural selection

- he published scientific papers on this theory with Darwin

what is wallace best known for?

- His work on warning colouration in animals (and how this must be a beneficial characteristic, evolved by natural selection)

- led to the development of speciation

Speciation definition

the process that results in the formation of a new species

speciation process

- when populations of the same species become so different that they are unable to interbreed and produce fertile offpring, they are considered different species and speciation has occurred

- due to natural selection

impact of darwin and wallace on modern biology

we now know that:

- all life forms change through evolution

- all life forms are descended from a common ancestor

Darwin's theory of evolution by natural selection

- variation exists within a species as a result of mutations in DNA

- organisms with characteristics most suited to the environment are more likely to survive to reproductive age and breed successfully- survival of the fittest

- the beneficial characteristics are then passed on to the next generation

- over many generations the frequency of alleles for this advantageous characteristic increase within the population until it becomes the norm

controversy surrounding darwin's theory of evolution

1. contradicted teh idea that god was the creator of all species on earth

2. there was not enough evidence at th etime

3. the mechanism of inheritance and variation were not known at the time

when are bacteria labelled as 'resistant'?

when they are not killed by antibiotics which previously were used as cures against them

explain bacterial resistance to antibiotics

- mutations during reproduction can result in the gene for antibiotic resistance

- exposure to antibiotics creates a selection pressure, as those with antibiotic resistant genes survive, and those without die

- as a result, those with antibiotic resistance can reproduce and pass on the advantageous gene to their offspring

how does antibiotic resistance support darwin's theory of natural selection?

as the new bacteria have been selected by the environment to have a feature (resistance) advantageous to survival

antibiotic resistance mark scheme

(1) by natural selection/evolution

(1) mutation in the bacteria

(1) only the resistant bacteria survived treatment by antibiotics

(1) the resistant bacteria reproduce

(1) offspring inherit the resistance

cause of antibiotic resistance

- overuse of antibiotics

- people don't finish the whole course of antibiotics

anti

ardi

- lived 4.4 million years ago

- fossilised skeleton has features a mixture of thos seen in apes and humans

--> walked upright, but had foot bone structure of an ape

how does ardi prove human evolution?

'intermediate' organism (somewhere between an ape and human) shows that natural selection, and eventually evolution, occured gradually

lucy

- lived 3.2 million years ago

- bone structure suggests that she walked upright, but had a small, chimp-like skull and brain

how does lucy prove human evolution?

represents another intermediate between apes and early humans

richard leakey's discovery of fossils

- in 1950s, leakey found found fossils from 1.6 million years ago

- including remnants of stone tools, and homo habilis, now considered one of the msot important early human species

how have tools developed over time?

over time, stone tools have become more worked, going from basic pebble tools, made by smashing rocks together, to pointed arrowheads, spears and hooks to carry out more complex tasks

how does the development of tools show evolution?

the greater development of tools show greater skill and therefore higher intelligence in more recent humans

how can tools be dated based on their environment?

- younger rock exists in earth layers towards the top, and older rock exists in layers lower down

- Tools can be compared with other fossils from known time period

- Rocks can be dated, e.g. radiometric dating

what is the limb with 5 digits called?

pentadactyl limb

how does the existance of pentadactyl limb prove evolution?

can be seen in a number of different organisms, implying that they all come from 1 common ancestor- and that each 'branched off' at some stage of evolution.

this could have been due to different selection pressures within different environments

systems to classify organisms (2)

1) Five Kingdoms system

2) Three Domains system

five kingdoms system

splits all organisms into:

- animals

- plants

- fungi

- prokaryotes

- protists

three domain system

splits everyone into three large groups:

- archaea

- bacteria

- eukaryota

why is three domain system better?

developments in science like the improvement of the microscope found that some species were more distantly related than first thought

selective breeding definition

when humans choose which organisms to breed in order to produce offspring with a certain desirable characteristics

process of selective breeding

1) breed two animals/ plants with the desired characteristic

2) select the offspring which also have this characteristics and breed

3) repeat the process over many generations

issues with selective breeding

inbreeding results in reduction in gene pool. This leads to:

--> less variation

--> more vulnerable to new diseases

--> increased chance in inheriting harmful genetic disorders

EXAM QUESTION: describe the method a scientist could use to grow plants that are tolerant to low levels of acid in the soil (2)

(1) prepare soil with a low level of acid

(1) put the seeds in the soil to grow

tissue culture definition

method of culturing living tissue outside the organism, within a growth medium

tissue culture process in plants

1) take the plant that you want to clone e.g. with desirable characteristics

2) using tweezers, remove a piece of tissue from a fast growing region of the plant e.g. meristem

3) using aseptic techniques, place the tissue on a special growth medium containing nutrients for optimum growth

4) once the tissue has developed enough, it can be transferred to compost for further growth

benefits of tissue culture

- allows plants with desirable characteristics to be produced:

--> cheaply

--> with greater yield

--> in a small space

--> quickly

--> at any time of the year

- for humans, can be used in medical research, without affecting a living organism

risks of tissue culture

- gene pool is reduced by producing clones (causes lack of variation, susceptability to disease etc)

- may lead to human cloning

genetic engineering definition

genetic engineering is modifying the genoe of an organism to introduce desirable characteristics

role of restriction enzymes in GM

used to cut out the genes and bacterial plasmid to give them corresponding sticky ends

role of sticky ends in GM

short section of unpaired bases

restriction enzymes make the gene's complimentary to the plasmid's

role of the vector in GM

the vector is the bacterial plasmid, into which the genes will be placed

role of ligase enzyme in GM

used to attach the sticky ends of the gene and the vector together

genetic engineering process

1) restriction enzymes isolates required gene, leaving it with sticky ends

2) the vector (e.g. a bacterial plasmid) is cut by the same restriction enzymes, leaving it with corresponding sticky ends

3) the plasmid (vector) and isolated gene are joined together by ligase enzyme

4) the genetically engineered plasmid is inserted into a bacterial cell

5) when the bacteria reproduce, the plasmids are copied as well, so it will be quickly spread and they will then express the gene and make the protein

how have crops been genetically modified to make them insect resistant?

- maize plants have been genetically modified with a gene for a toxin that kills many insect larvae harmful to the crop

- the toxin is called Bt toxin, taken from the bacterium bacillus thuringiensis

- known as Bt corn

- this results in an increase in yield and cheaper because less pesticides are used

benefits of genetic modification (4)

1) in medicine- can cure inherited disorders

2) improves yields in agriculture by making them resistant to insects, herbicides or different conditions

3) crops with extra vitamins can be produced where people lack them e.g. golden rice

4) greater yields can help world hunger

risks of genetic modification (3)

- increased costs for GM seeds

- risk of inserted genes being transferred to wild plants which could reduce the usefulness of the GM crop

- pose a selection pressure to other species

how can farmers increase their crop yield?

1) fertilisers

2) biological control

advantage of fertilisers

can make crops grow faster and bigger so that yields are increased

disadvantage of fertilisers

excess fertilisers not taken up by crops can get washed into lakes and rivers and cause eutrophication

biological control

the intentional release of a natural enemy to attack a pest population

advantages of biological control (3)

- can have longer-lasting effects than chemical pesticides

- be less harmful to the environment e.g. to non-target species

- Only has to be applied once

disadvantage of biological control (2)

- doesn't completely remove the pest, just keeps it at lower levels

- can turn into a pest themselves

name all the different types of genetic engineering (3)

1) genetic modification

2) selective breeding

3) tissue culture

advantages of genetic engineering as a whole

- can be used in medicine to mass-produce certain hormones using microorganisms

- xenotransplantation

- make crops resistant to droughts or herbicides to increase yield

- crops can produce their own pesticides (e.g. Bt corn)

disadvantages to genetic engineering as a whole

- difficult to predict the effects of modifying the genome of an organism

- could lead to GE in humans (e.g. 'designer babies'), having many ethical implications

- genes from GM crops could spread to the environment

- GM crops create a selection pressure, leading to pesticide resistance evolving in pest species