Topic 4 - Natural Selection and Genetic Modification✅

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Describe the work of Charles Darwin and Alfred Wallace

• Alfred Wallace believed that individuals who do not have characteristics to help them survive a change in the environment would die out

• He published joint studies with Darwin, who received the credit

• He continued work across the world, collecting evidence for the theory

• Much more evidence over time has resulted in our current understanding

Why were some people against Darwin's theory back then

• It was against the idea that God created all organisms on earth

• There was not much evidence at the time

Explain Charles Darwin's theory of evolution

Natural selection

• Individuals in any population show genetic variation due to differences in their alleles

• These arise randomly due to mutations

• Populations experience limited resources or a change in their environment known as a selection pressure

• There is competition for these resources

• Individuals with the characteristics best suited to their environment are more likely to survive, reproduce, and pass on their alleles

• Over time the frequency of this allele will increase among the population

Explain the process of antibiotic resistance in bacteria

• A mutation within the gene of some of the bacteria causes the bacteria to be resistant to antibiotics.

• As they are resistant, it means these bacteria will survive because the antibiotics won't kill them.

• The resistant ones have a selection advantage over the ones that are unresistant.

• The resistant ones that survive will reproduce.

• While reproducing, they will pass down the allele that gives the bacteria resistance to antibiotics.

• Over time, the allele that gives the bacteria resistance to antibiotics will become more frequent

How does Ardi give us evidence for human evolution

• Ardi was estimated to have lived 4.4. million years ago

• His skeleton contains many 'humanoid' features but also resembles an ape

• Ardi is evidence that natural selection and evolution are gradual processes

• The bone structure in Ardi's feet is different to chimpanzees, suggesting that the two evolved separately

How does Lucy give us evidence for human evolution

• Lucy was estimated to have lived 3.2 million years ago

• Her bone structure suggests she walked in an upright position

• However her chimp-like skull and brain suggests she, like Ardi, was an intermediate between apes and early humans

How do Richard Leakey's findings give us evidence for human evolution

• Richard, Mary and Louis Leaky found fossils in the 1950s

• Some of these fossils contained remnants of stone tools and of the Homo habilis

• The homo habilis is considered one of the most important early human species

How do stone tools give evidence of human evolution

• Thanks to archaeological digs, we can find stone tools which give us a rough guide on human evolution, because the tools have become more complex as our brains have evolved

• The early stone tools were basic and used for simple purposes like cracking nuts

• The more advanced stone tools were sharper and enabled more advanced tasks to be carried out, such as catching fish

How can stone tools be dated (rcd)

• We can use radiometric carbon dating

• By looking at the natural radioactive decay of an isotope, we can estimate how long ago an organism lived

• This works if a living material is found in a tool e.g. A piece of wood

How can stone tools be dated (srl)

Stratifying rock layers

• You can look at the layer of sediment that the stone tool was found in

• Each layer of sediment and everything in it was formed at the same time

• By dating the fossils in the sediment layer, we can estimate when the tools were formed

How does the anatomy of the pentadactyl limb give scientists evidence for evolution

• The pentadactly limb is a limb with five digits

• This can be seen in a number of organisms like cats, horses, birds, and humans

• This means that all these organisms come from a common ancestor

○ And each organism branched off at some stage, due to selection pressure

How has genetic analysis led to the use of the three domains rather than the five kingdoms as a classification method

• Developments in science, like the improvement of the microscope and the increased knowledge of biochemistry, found that some species were more distantly related than first thought

• It has been demonstrated that some organisms have parts of their genes that are not used in making proteins and other organisms use entire genes to code for proteins, with no unused portions.

• So three large groups, called domains, were created above kingdoms

What are the three domains

Archaea, Bacteria, Eukaryota

What is selective breeding

• Selective breeding is when humans choose which organisms to breed, in order to produce offspring with a certain desirable characteristic

• (e.g animals with more meat, plants with disease resistance or big flowers)

Selective breeding impact on food plants

• The gene pool is smaller

• This means if the environment changes or there is a new disease, the whole species could go extinct

Selective breeding impact on domesticated animals

• Small gene pool leads to a greater chance of genetic defects

• This is because recessive characteristics are more present

• Domesticated animals have a much higher frequency of genetic conditions than normal

What is tissue culture

The method of culturing living tissue by making it grow outside the organism, within a growth medium

Describe the process of tissue culture

• A piece of tissue from a fast growing region of the plant (e.g. Root) is removed using tweezers

• The tissue is placed on a sterile growth medium that contains hormones and nutrients

• Plant hormones are added to encourage the growth of roots and shoots to form plantlets.

• Once these plants are large enough, they can be transferred to soil or a greenhouse.

Benefits of tissue culture

• Produces lots of offspring with desirable characteristics

• Increases crop resistance which increases crop yield

• Can help extremely endangered species

Risks of tissue culture

• When you use clones, genetic variation decreases, making the species less likely to survive if disease hits

• Clones have a low survival rate and often have genetic problems

How can tissue culture be helpful in human medical research

• human tissue can also be grown for testing drugs or new chemicals.

• It is needed to study viruses, as they cannot replicate outside of cells

• Cultures of cancer cells help our understanding of how they grow and spread

What is genetic engineering

• Modifying the genome of an organism

• by introducing a gene from another organism to give a desired characteristic.

How have plant cells be genetically engineered

Plant cells have been engineered for disease resistance or to have larger fruits

How have bacteria cells been genetically engineered

• Bacterial cells have been engineered to produce substances useful to humans,

• such as human insulin to treat diabetes.

Explain the stages of genetic engineering

• First the desired gene is removed from the DNA, using restriction enzymes.

• Then cut with a jagged edge to make sticky ends - this means there are exposed bases.

• Inside a bacterium is a plasmid (small loop of DNA), which can be removed and cut open using the same restriction enzyme

• The desired gene can then be inserted into the plasmid.

• The exposed bases will be complementary so can bond easily.

• Ligase enzyme is then used to join the rest of the molecule together

• The plasmid is now a vector and contains recombinant DNA.

• It can be returned to a bacteria.

• The bacteria is a genetically modified organism

Advantages of genetic engineering to make GM crops

• Improve growth rates

• Introduce modifications to allow crops to grow in diff conditions, or allow plants to make their own pesticides

• Makes a greater yield

Disadv of genetic engineering to make GM crops

• We don't understand the effects of GM crops on human health

• They pose a selection pressure, leading to increased resistance in other species like pests

• Growing with pesticides can kill insects and other plants

• GM crops' infertility may spread to other species

Why are BT crops used

• BT is a bacteria that produces toxins to kill larvae

• This is useful for crops, so we insert BT genes into crops to increase their insect resistance

• This means the crop will produce the BT toxin, so less crops get eaten by insects

• this increases crop yield

Advantages of BT crops

Increases crop yield and profits

Disadv of BT crops

• Could pose health risks to humans

• Killing insects results in loss of biodiversity

Why are fertilisers needed

• Plants and crops take in mineral ions from the soil, which are needed to make proteins and DNA

• As crops are harvested the soil contained less and less minerals ions

• For more plant growth, fertilisers are necessary because they add the mineral ions back into the soil

Advantages of fertilisers

• Increase crop yield

• Control amount of nutrients in the soil

Disadv of fertilisers

Can lead to eutrophication

Describe the process of eutrophication

• Fertiliser leaches into bodies of water

• Fertilisers are rich in nutrients, leading to an increase in algae growth

• Lots of algae blocks the sunlight from getting to organisms below the surface of the lake

• These plants can't photosynthesise, so they die

• Decomposing microorganisms, combined with the lack of photosynthesising organisms, reduces the amount of oxygen in the lake

• This means animals like fish can't respire because there isn't enough oxygen

• Therefore the fish will die

What is biological control

Biological control is the use of natural predators to reduce pest populations

Adv of biological control

• Pests do not develop resistance

• Do not need to be reapplied

• Are often specific to a certain pest

Disadv of biological control

• Will compete with other species for food

• Cannot control where they go

• May become a pest themselves

• Takes a long time to be effective

Benefits of genetic engineering in agriculture

• Leads to greater crop yields, helping to solve world hunger

• Modifications can allow crops to grow in different conditions (e.g. Hotter than usual)

• Modification can allow plants to make their own pesticide

Benefits of genetic engineering in medicine

It can be useful to mass produce certain hormones in microorganisms

Risks of genetic engineering in agriculture

• GM crops are infertile and these genes could spread to other plants, leading to infertility in other species

• This has a knock on effect on the environment

• We do not fully understand the effects of GM crops on human health

• Genetic engineering in agriculture could make it a popular thing in humans, leading to designer babies etc

• GM crops pose a selection pressure, meaning species like pests increase their resistance

Benefits of selective breeding in agriculture

• increases the yield of particular crop - by selectively breeding individuals that produce a high quality or mass of food

• Individual plants or animals can be bred to be resistant to disease, increasing crop yield

Risks of selective breeding in agriculture

• Selecting for certain characteristics can cause health problems

• E.g. Chickens that have been bred to have more meat are sometimes to large, meaning they can't walk

• Lack of genetic variation, meaning the entire population could be wiped out if a disease hits

• It is unethical to breed animals so that they have characteristics wanted by humans, but a worse quality of life

Describe archaea

• Primitive bacteria

• Do not have a nucleus

• Have unused sections of genes

Describe bacteria

• True bacteria

• Do not have a nucleus

• Do not have unused sections of genes

Describe Eukaryota

• Protists, fungi, plants, animals

• Have a nucleus

• Have unused sections of genes