B15 Genetics and Evolution

Question 1

What is Darwin Theory of Evolution?

Answer 1

• Individuals in a species show a wide range of variation caused by differences in genes
• Individuals with characteristics most suited to the environment have a higher chance of survival and more chances to reproduce
• Therefore these characteristics are passed to their offspring at a higher rate than those with characteristics less suited to survival
• Over many generations, these beneficial characteristics become more common in the population and the species changes (the species evolves)
  This idea of natural selection became known as ‘survival of the fittest’

Question 2

What is the title and year of publication of Darwin’s book?

Answer 2

Darwin published his ideas in his famous book, On the Origin of Species (1859)

Question 3

What is Lamark’s Theory?

Answer 3

Lamark developed his theory at the start of the 19th century (before Darwin announced his theory).
Lamarck’s theory was based mainly on the idea that changes that occur in an organism during its lifetime can be inherited
His theory involved two main ideas:
- a characteristic that is used frequently by an organism becomes better and stronger, whereas a characteristic that isn’t used gradually disappears
- the beneficial characteristics that are used frequently (and are improved as a result) are passed to offspring
For example, Lamarck suggested that:
Giraffes had a short-necked ancestor that would frequently stretch its neck to reach the high branches so it could feed on the leaves
This repeated stretching could very slowly elongate the giraffe’s neck and that this would be passed to the giraffe’s offspring
Over time and many generations, the giraffe would evolve to have the very long neck it has today
We now know that in the vast majority of cases this type of inheritance cannot occur and that Lamarck’s ideas were incorrect

Question 4

Why did people object to Darwin’s theory?

Answer 4

The theory of evolution by natural selection was only gradually accepted because:
- There was much controversy surrounding these revolutionary new ideas
- The theory challenged the idea that God made all the animals and plants that live on Earth
- There was insufficient evidence at the time the theory was published to convince many scientists
- There was no way to explain how variety and inheritance happened. There was still no way to explain how characteristics were inherited. The mechanism of inheritance and variation (genetics) was not known until 50 years after the theory was published
- The theory of evolution by natural selection developed over time and from information gathered by many scientists

Question 5

Who was Alfred Russel Wallace?

Answer 5

Alfred Russel Wallace was a scientist who, after conducting his own travels around the world and gathering much evidence, independently developed his own theory of evolution based on the process of natural selection.
He published scientific papers on this theory with Darwin in 1858 (Darwin published his book, On the Origin of Species, the following year).
Wallace is best known for:
- His work studying the warning colouration of species (particularly butterflies) and how this must be an example of a beneficial characteristic that had evolved by natural selection, as the warning colouration helps to deter predators
- Developing the theory of speciation

Question 6

What is Wallace’s theory of speciation?

Answer 6

Speciation is a process that results in the formation of a new species.
When populations of the same species become so different that they are unable to interbreed and produce fertile offspring, they are considered different species and speciation has occurred.
Speciation can occur as a result of a combination of isolation (when populations of the same species become separated) and natural selection.
Populations of the same species can become isolated from one another due to the formation of a physical barrier (eg. a new river or mountain range) – this is known as geographic isolation.
The environment will be different on either side of this physical barrier (eg. different climates or different food available)
The environmental differences on either side will provide different selection pressures and natural selection will cause a different set of characteristics to become more common in the two isolated populations
Over many generations, individuals from the two populations will have become so distinct (genetically, behaviorally, physically) that they will no longer be able to interbreed and produce fertile offspring.
The two populations are now separate species.

Question 7

What are fossils?

Answer 7

Fossils are the ‘remains’ of organisms from millions of years ago, which are found in rocks, ice and other places

Question 8

How are fossils formed?

Answer 8

1. When an animal or plant does not decay after it has died. This can happen for a number of reasons. For example: there is little oxygen present, there are poisonous gases that killed the bacteria responsible for decay, temperature too low for decay to take place. These fossils are rare
2. Many fossils are formed when harder parts of the animal/ plant are replaced by minerals as they decay and become part of the rock. Rock fossils are the most common
3. Some fossils are not animals or plants but traces they have left behind. For example footprints

Question 9

When are mould fossils formed?

Answer 9

When an impression of an organism is made in mud and then becomes fossilised

Question 10

Why is there only a limited amount of fossils?

Answer 10

• Many of the early organisms where soft bodied. These means they have left no fossil trace
• Geological activity such as formation of mountain ranges, volcanoes etc might have destroyed the first fossils
• Most organisms that died where not fossilised, as the right conditions are rare
• some still needs to be found

Question 11

Why scientists cannot be certain about how life began on Earth

Answer 11

Not enough fossils

Question 12

When does extinction occur?

Answer 12

Extinction occur when there are no remaining individuals of a species still alive

Question 13

Why does extinction occur?

Answer 13

Species that are poorly adapted to their environment are less likely to survive and reproduce compared to species that are well adapted to their environment.
If they are unable to survive and reproduce sufficiently to maintain their population numbers they will eventually go extinct.

Question 14

What causes extinction?

Answer 14

There are many causes but they always involve a change in the environment of the organism:
temperature change
new predators
new disease
more successful competitors

Question 15

What has been the main cause of extinction throughout history?

Answer 15

Changes to climate or to the environment

Question 16

What is meant by mass extinction?

Answer 16

It is when many or even most species on earth die out. Evidence suggests these are caused by a single catastrophic event. There have been 5 occasions in which this has happened.

Question 17

What caused dinosaurs to get extinc?

Answer 17

Dinosaurs are an example of mass extinction.
- Some scientists agree that 65 millions years ago a giant asteroid collided with earth in Mexico. Here there is a huge crater (180km in diameter). Also, deep below the crater lots of iridium was found. This is a mineral that forms only when rock is hit with massive force.
The asteroid impact would have cause earthquakes, tsunamis, landslides. Enormous amt of material would have been sent in the athmosphere. This made everywhere almost dark. PLants struggled survive. Temperature dropped. Between 50 and 70% of all living species died out.
- Some Uk scientists think that extinction started sooner (137m years ago) and it was a slow process. They believe that global warming caused melting of sea ice. Temperature dropped by 9 degrees and caused mass exctinction. Evidence: unexpected change in fossils and minerals in areas of Norway.

Not easy to build a theory. Probably both of them are correct.

Question 18

What is a very clear piece of evidence for evolution?

Answer 18

One very clear piece of evidence for evolution is antibiotic resistance in bacteria

Question 19

How do bacteria become resistant to antibiotics?

Answer 19

Like all other organisms, within a population, there will be variation caused by mutations.
A chance mutation might cause some bacteria to become resistant to an antibiotic (eg penicillin)
When the population is treated with this antibiotic, the resistant bacteria do not die
This means they can continue to reproduce with less competition from non-resistant bacteria, which are now dead
Therefore the genes for antibiotic resistance are passed on with a much greater frequency to the next generation
Over time the whole population of bacteria becomes antibiotic-resistant because the bacteria are best suited to their environment

Question 20

What has facilitated bacteria antibiotic resistance?

Answer 20

• overuse of antibiotics in situations where they were not really necessary, for example:
  For the treatment of non-serious infections
  Routine treatment to animals in agriculture
  Failure to finish the prescribed course of antibiotics

Question 21

What can be done to prevent more resistant strains of bacteria appearing?

Answer 21

• Do not overuse antibiotics. Now they are not prescribed for minor infections
• Finish the course so all bacteria are killed
• restrict agricultural use of antibiotics to prevent the spread of antibiotics resistance from animal to human pathogens. In the US, however, 70% of human antibiotics are used on farm animals to boost growth and prevent (rather than cure) infections

Question 22

What is MRSA?

Answer 22

It is a very dangerous bacterial strain that is resistant to
most antibiotics. It is present in hospitals and in the early 21st century it was causing 1000 death a year in UK hospitals and care homes.

Question 23

Precautions to limit spread of MRSA in hospitals

Answer 23

• Medical staff to wash hand with soap and water or alchol gel between patients and wear disposable cloths or cloths which are sterilised
• high standard of hygiene
• patient infected should be in isolation
• visitors wash hands when they arrive and leave

Question 24

Since there is antibiotics resistance cannot we simply discover new antibiotics?

Answer 24

Some scientists are worried we may not be able to keep up with the demand for new antibiotics, as more and more antibiotic-resistant strains evolve:
- Developing new antibiotics is also a very costly process
- It is not easy to find chemicals that kill bacteria without damaging the cells (for example peniccilin come from a microorganism not from chemicals)

Question 25

What is meant by classification?

Answer 25

It is the organisation of living things into groups according to their similarities

Question 26

When did classification begin?

Answer 26

Organisms were first classified by a Swedish naturalist called Linnaeus in the 18th century.

Question 27

How did Linnaeus classify organisms?

Answer 27

He grouped organisms together based on their structure and characteristics

Question 28

What is the name of Linnaeus classification system?

Answer 28

Natural classification system

Question 29

What are the groups used by Linnaeus to classify organisms?

Answer 29

Kingdom, Phylum, Class, Order, Family, Genus, Species

Question 30

How did Linnaeus name organisms?

Answer 30

He named organisms in Latin using the binomial system where the scientific name of an organism is made up of two parts starting with the genus (always given a capital letter) and followed by the species (starting with a lower case letter).
The two names are underlined when written or in italics when printed

Question 31

What were the kingdom suggested by Linnaeus and why?

Answer 31

He only suggested 2 kingdoms: Animals and plants. This is because the known type of living things was less that today and also because originally, organisms were classified using morphology (the overall form and shape of the organism, e.g. whether it had wings or legs) and anatomy (the detailed body structure as determined by dissection).

Question 32

What is the system accepted today?

Answer 32

Six kingdoms

Question 33

What are species?

Answer 33

A species is defined as a group of organisms that can reproduce to produce fertile offspring

Question 34

What is a domain?

Answer 34

This is a new higher level of classification above kingdom which was introduced in the 1970s by Woese. The evidence from this idea comes from a detailed analysis of cells ribosome and the way different cells reproduce.
Woese proposed 3 domains in turn divided into 6 kingdom:
- Archaea (primitive bacteria usually living in extreme environments such as hot springs and salt lakes)
- Bacteria (true bacteria such as coli and Staphylococcus)
- Eukaryota (which includes protists, fungi, plants and animals)

Question 35

What is Archaea?

Answer 35

It is one of the domains by Woese. These are primitive forms of bacteria. This domain contains one kingdom: the archaebacteria

Question 36

What are bacteria?

Answer 36

It is one of the domains by Woese. These are true bacteria and the cyanobacteria (those that can photosynthetise). It contains one kingdom: the eubacteria

Question 37

What are eukariota?

Answer 37

It is one of the domains by Woese. organisms with a cell that contains a nucleus with genetic material. There are 4 kingdoms: protista, fungi, plants and animals

Question 38

What are evolutionary trees?

Answer 38

Evolutionary trees are diagrams that show the relationship between species over evolutionary time. They are built by looking at similarities and differences between different groups of organisms. Now scientists look at DNA to do this in a reliable manner