Topic 4 - Natural Selection And Genetic Modification

Question 1

What is Charles Darwin’s theory of evolution by natural selection?

Answer 1

More individuals are produced each generation that can survive.
Phenotypic variation exists among individuals and the variation is heritable.
Those individuals with heritable traits better suited to the environment will survive.
When reproductive isolation occurs new species will form.

Question 2

What is meant by natural selection?

Answer 2

“Survival of the fittest”
Things like predation, competition for resources and disease act as selection pressures. This means they affect an organism’s chance or surviving and reproducing.
Individuals with characteristics that make them better adapted have more chance of surviving& more likely to bread successfully.

Question 3

How does bacteria provide evidence for evolution?

Answer 3

Bacteria sometimes develop random mutations in their DNA- which can create new alleles that change the bacterias characteristics.
E.g. A bacterium could become less affected by a particular antibiotic
Antibiotic resistance provides evidence for evolution because it makes the bacteria better adapted to an environment in which antibiotics are present. As a result, antibiotic resistance becomes more common in the population over time. The emergence of other resistant organisms also provides evidence for evolution.

Question 4

How do fossils provide evidence for evolution?

Answer 4

By arranging fossils in chronological order, gradual changes in organisms can be observed. This provides evidence for evolution because it shows how species have changed and developed over billions of years.

Question 5

How do fossils relate to human ancestors?

Answer 5

Evidence from fossils suggests that humans and chimpanzees evolved from a common ancestor that existed around 6 million years ago.
These fossils have characteristics that are between apes and humans & by looking at hominid fossils you can see how humans have evolved over time

Question 6

What are hominids?

Answer 6

Human beings and their ancestors

Question 7

Who is Ardi?

Answer 7

Ardi is a fossil hominid of the species Ardipithecus ramidus. She is 4.4 million years old and she was found in Ethiopia. Ardi’s features are a mixture of human and apes

Question 8

What are Ardi’s features?

Answer 8

1) the structure of her feet suggests she climbed trees - she had an ape-like big toe to grasp branches
2) she had long arms and short legs and her brain size was about the same as a chimpanzee’s
3) the structure of her legs suggests she walked upright. The structure of her hand bones suggests she didn’t use her hands to help her walk

Question 9

Who is Lucy?

Answer 9

Lucy is a fossil hominid of the species audtralopithecus afarensis. She was found in Ethiopia and is 3.2 million years old. She had a mixture of human and ape features, however she is more human-like than Ardi.

Question 10

What are Lucy’s features?

Answer 10

1) Lucy had arched feet, more adapted to walking than climbing
2) the size of her arms and legs was between what you would expect to find in apes and humans
3) her brain was slightly larger than Ardi’s but similar in size to a chimp’s brain
4) the structure of Lucy’s leg bones and feet suggest she walked upright, more efficiently than Ardi

Question 11

Who was Leakey?

Answer 11

In 1984 scientist Richard Leakey organised an expedition to Kenya to look for hominid fossils. Leakey and his team found fossil hominids 1.6 millions years old.

Question 12

Describe the features of Turkana Boy - one of Leakey’s discoveries?

Answer 12

Turkana boy was a 1.6 million year old fossil skeleton of the species homo erectus. He has a mixture of human and ape-like features, but is more human-like than Lucy.

• His short arms and long legs are much more human than ape and his brain size was much larger than Lucy’s (similar to human)
• The structure of his legs and feet suggested he was even better adapted to walking upright than Lucy

Question 13

What’s the timeline of fossils?

Answer 13

4. 4 million years ago = Ardi = ardipithecus species
5. 2 million years ago = Lucy = Australopithecus species
6. 6 million years ago = Turkana boy = homo species

Today = us = Homo sapiens

Question 14

How do stone tools provide evidence for human evolution?

Answer 14

The different homo species continued to evolve, you can tell this because they started using stone tools and these gradually became more complex. Therefore their brains must have been getting larger

Question 15

What is the timeline of homo species and tool use?

Answer 15

2.5-1.5 million years ago = homo habilis

2-0.3 million years ago = homo erectus

300000-25000 years ago = homo neanderthalis

200000 years ago - present = Homo sapiens

Question 16

What was homo habilis (2.5-1.5million years ago) use of stone tools?

Answer 16

Made simple stone tools called pebble tools by hitting rocks together to make sharp flakes. These could be used to scrape meat from bones or crack bones open

Question 17

What was homo erectus (2-0.3million years ago) use of stone tools?

Answer 17

Sculpted rocks into shapes to produce more complex tools like simple hand-axes. These could be used to hunt, dig, chop and scrape meat from bones

Question 18

What was homo neanderthalis (300000-25000 years ago) use of stone tools?

Answer 18

More complex tools. Evidence of flint tools, pointed tools and wooden spears

Question 19

What are Homo sapiens (200000 years ago - present) use of stone tools?

Answer 19

Flint tools widely used. Pointed tools including arrowheads, fish hooks, buttons and needles appeared around 50000 years ago

Question 20

How can scientists work out how old stone tools or hominid fossils are?

Answer 20

1) looking at the structural features of the tool or fossil (simpler tools = older)
2) using stratigraphy- the study of rock layers. Older rock layers are normally found below younger layers, so tools or fossils in deeper layers are usually older
3) stone tools are often found with carbon-containing material

Question 21

What is classification?

Answer 21

Organising living organisms into groups

Question 22

How are organisms classified?

Answer 22

Organisms were classified according to similarities and difference in their observable characteristics. This now includes what can be seen with microscopes.
These characteristics were used to classify organisms in the five kingdom classification system.

Question 23

What are kingdoms?

Answer 23

Kingdoms are the five groups living things are divided into.

Animals 
Plants
Fungi
Prokaryotes
Protists

Question 24

What are examples of animals?

Answer 24

Fish, mammals, reptiles

Question 25

What are examples of plants?

Answer 25

Grasses, trees

Question 26

What are examples of fungi?

Answer 26

Mushrooms and toadstools, yeasts

Question 27

What are prokaryotes?

Answer 27

All single-felled organisms without a nucleus

Question 28

What are Protists?

Answer 28

Eukaryotic single-felled organisms

E.g algae

Question 29

What are the kingdoms subdivided into?

Answer 29

The kingdoms are then subdivided into smaller and smaller groups that have common features

Phylum
Class
Order
Family
Genus
Species

Question 30

How have classification systems changed over time? (Genetic analysis)

Answer 30

Over time, technology has developed further and our understanding of things like biochemical processes and genetics has increased. This led to a rethink in the way organisms are classified and to the proposal of the three domain system of classification by a scientist called Carl Woese. Using genetic analysis, Woese found that some members of the Prokaryote kingdom weren’t as closely related as thought. He suggested organisms should be divided into three large groups called domains. The three domains are subdivided into kingdom - species

Question 31

What are the three domains?

Answer 31

1) Archaea - organisms in this domain look similar to bacteria but are actually quite different - as differences in their genetic sequences show. They were first found in extreme places such as hot springs and salt lakes
2) Bacteria - this domain contains true bacteria. E.g. Coli
3) Eukarya - this domain includes a broad range of organisms including fungi, plants, animals and protists

Question 32

What is selective breeding?

Answer 32

Selective breeding is when humans artificially select the plants or animals that are going to breed so that the genes for particular characteristics remain in the population.

Question 33

What are examples of desirable features from being selectively bred?

Answer 33

Organisms are selectively bred to develop features that are useful or attractive:

• animals that produce more meat or milk
• crops with disease resistance
• dogs with a good, gentle temperament
• plants that produce bigger fruit

Question 34

What is the process in order to selectively breed an organism?

Answer 34

1) from your existing stock select the ones which have the characteristics you’re after
2) breed them with each other
3) select the best off the offspring and breed them together
4) continue this process over several generations and the desirable trait gets stronger and stronger. Eventually all the offspring will have the characteristics

Question 35

How is selective breeding useful in agriculture?

Answer 35

Genetic variation means some cattle will have better characteristics for producing meat than others. To improve meat yields, a farmer could select cows and bulls with these characteristics and breed them together. After doing this, the farmer would get cows with a very high meat yield

Question 36

How is selective breeding useful in medical research?

Answer 36

In several studies investigating the reasons behind alcoholism, rats have been bred with either a strong preference for alcohol or a weak preference for alcohol. This has allowed researchers to compare the differences between the two different types of rats, including difference in their behaviour and in the way their brains work

Question 37

What are the disadvantages of selective breeding?

Answer 37

• reduces the gene pool - the number of different alleles in a population. This is because the best animals or plants are always used for breeding and they are all closely related. - inbreeding
• can cause health problems - as there’s more change of the organisms inheriting harmful genetic defects when the gene pool is limited. This can lead to ethical considerations
• problem if a new disease occurs - all the stock are closely related so if one is going to be killed by a disease it’s likely the others will succumb to it

Question 38

What is genetic engineering?

Answer 38

A process which involves modifying the genome of an organism to introduce desirable characteristics

Question 39

What are restriction enzymes?

Answer 39

Restriction enzymes recognise specific sequences of DNA and cut the DNA at these points - the pieces of DNA are left with sticky ends where they have been cut

Question 40

What is ligase?

Answer 40

Ligase enzymes are used to join two pieces of DNA together at their sticky ends

Question 41

What is recombinant DNA?

Answer 41

Two different bits of DNA stuck together

Question 42

What’s the role of enzymes in genetic engineering?

Answer 42

Enzymes can be used to cute up DNA or join DNA pieces together

Question 43

What is a vector?

Answer 43

A vector is something that’s used to transfer DNA into a cell. There are two sorts - plasmids and viruses

Question 44

What are plasmids?

Answer 44

Plasmids are small, circular molecule of DNA that can be transferred between bacteria

Question 45

What are viruses?

Answer 45

Viruses insert DNA into the organisms they infect

Question 46

How does genetic engineering work?

Answer 46

1) the DNA you want to insert is cut out with a restriction enzyme. The vector DNA is then cut open using the same restriction enzyme.
2) the vector DNA and the DNA you’re inserting are left with sticky ends. They’re mixed together with ligase enzymes.
3) the ligases join the pieces of DNA together to make recombinant DNA
4) the recombinant DNA is inserted into other cells
5) these cells can now use the gene you inserted to make the protein you want

Question 47

What are the benefits of genetic engineering?

Answer 47

• crops can be genetically modified to be resistant to herbicides. Making crops herbicide resistant means farmers can spray their crops to kill weeds, without affecting the crop itself. Can increase crop yield
• In medicine, researchers have managed to transfer human genes that produce useful proteins into sheep and cows. These proteins can be extracted from the animal. Animals that have organs suitable for organ transplantation into humans might also be produced in the future

Question 48

What are the risks of genetic engineering?

Answer 48

• it can be hard to predict what effect modifying its genome will have on the organism - many genetically modified embryos don’t survive and some genetically modified animals suffer from health problems later in life
• concerns about growing genetically modified crops - transplanted genes may get out into the environment. Genetically modified crops could adversely affect food chains or human health