GCSE Edexcel Combined Science- Biology Topic 4 - Natural Selection and Genetic Modification

The theory of evoloution

Organisms have changed over time

Genetic Variation

The characteristics of individuals vary due to differences in genes

Competition

When organisms need the same resources as each other, they struggle against each other to get those resources

Natural Selection

A process in which certain organisms are more likely to survive and reproduce than other members of the same species because they possess certain genetic variations.

Inheritance

The survivors breed and pass on their variations to their offspring. Therefore, the next generation contains more individuals with 'better adapted variation'.

Antibiotics

Medicine that helps people recover from bacterial infection by killing the pathogen

Are antibiotics effective against viruses?

No

Explain how antibiotic resistance occurs as a result of ending due to stopping an antibiotic course too early

1) In a population of bacteria, some bacteria are naturally more resistant to an antibiotic due to genetic variation (random mutations)

2) The antibiotic course starts. With time, the antibiotic kills more and more bacteria. The most resistant bacteria takes the longest time to die.

3) The person stops the course because they feel better. However, this leaves the most resistant antibiotics to survive. These resistant antibiotics then reproduce and pass these alleles for resistance against the antibiotic to the new generation. The alleles are inherited. The new generation is now resistant to the antibiotic.

Explain Antibiotic resistance

1) A random mutation provides resistance to an antibiotic

2) Bacteria with resistance alleles survive and reproduce

3) A new strain of antibiotic-resistant bacteria has arisen

Evoloution

A gradual change in the characteristics of a species over time

What are fossils used for

To find out more about evolution

Ardi's height

1.2m

Ardi's weight

50kg

How old is Ardi

4.4 million years old

An animal with the same brain size as Ardi

Chimpanzee

What does Ardi's bone structure show

May have walked and probably climbed trees

Lucy's height

1.07m tall

How old is Lucy

3.3 million years old

What did the fossils show about Lucy

probably walked upright

Richard Leakys discovery

Found a 1.6 million-year-old homo erectus, who was 1.79m tall and would've walked upright more efficiently than Lucy

What did the development of genetic analysis show

All organisms apart from prokaryotes had unused sections in DNA

The 3 domains

Archaea, Bacteria and Eukarya

Selective breeding (artificial selection)

When humans choose an organism that has a certain characteristic and breed more of these organisms, making that chosen characteristic more and more obvious

Plants and animals are often selectively bred for

disease resistance, yield, fast growth, flavour

Genetic Engineering/Modification

The process of altering the genome of an organism to produce desirable traits, usually by adding genes from another species.

Genetically Modified Organism (GMO)

An organism that had its genome artificially altered

Sticky Ends

A short section of unpaired bases, made by restriction enzymes cutting the DNA

The process of genetic engineering (first step)

Identify the gene that needs to be inserted. Allows scientists to know which DNA code needs to be cut in order to extract the required gene.

The process of genetic engineering (second step)

The gene can be cut out of the rest of the DNA using restriction enzymes. These enzymes break the bond in the DNA backbone, exposing DNA bases at the site of the cut, creating areas called sticky ends (unpaired bases). Sticky ends can easily bind to other exposed bases due to complementary base pairing.

The process of genetic engineering (third step)

The next step is to prepare the bacterial plasmid. The plasmid is cut with the same restriction enzyme. This is done to ensure that they have the same sticky ends for complementary base pairing.

The process of genetic engineering (fourth step)

We can take the prepared insulin gene and insert it into the gap in the plasmid. The bases join together by complementary base pairing. Ligase is the enzyme that joins the plasmid and insulin gene together. It is the 'glue'. It works by helping form chemical bonds between the sticky ends. the new DNA produced is called recombinant plasmid because it contains DNA from two species.

The process of genetic engineering (fifth step)

The recombinant plasmid is inserted into a bacterial cell, which can read the DNA and produce the desired protein (insulin).

The process of genetic engineering (sixth step)

The new, genetically modified bacteria is placed into nutrients, where it can reproduce asexually and increase the population of the genetically modified bacteria.

Pros of selective breeding

- Yield of crops can be significantly increased

- Crops can be bred for disease resistance, which also increases yield

Cons of selective breeding

- Can produce health problems in organisms, which is seen as unethical. e.g. some selectively bred chickens have so much breast meat they cannot stand up.

- Results in reduction of gene pool, causing inbreeding which causes harmful genetic defects

- Similar genes mean if one organism is vulnerable to a disease, the rest will be too

Pros of genetic engineering

- Can be used in medicine to mas produce hormones (insulin)

- May be used in future to produce animals with organs suitable for human transplant

- Can be used to produce crops that are beneficial to the poor e.g. beta carotene

- Can be used to produce crops that produce their own herbicide

Cons of genetic engineering

- Difficult to predict unwanted effects

- ethical implications (designed babies)

Restriction Enzymes

Enzymes that cut DNA molecules into pieces

Ligase

An enzyme that joins 2 DNA molecules together

Vector

Any DNA molecules used to carry new DNA into another cell