B14 Variation and Evolution

Question 1

What is variation?

Answer 1

Variation is defined as differences between individuals of the same species

Question 2

What can variation be caused by?

Answer 2

It can be genetic– controlled entirely by genes (this is called genetic variation)
It can be environmental – caused entirely by the environment in which the organism lives
Or it can be due to a combination of genes and the environment

Question 3

What are examples of genetic variations?

Answer 3

Examples of genetic variation in humans include:
blood group
eye colour
gender
ability to roll tongue
free or fixed ear lobes

Question 4

What are examples of environmental variation?

Answer 4

Characteristics of all species can be affected by environmental factors such as climate, diet, accidents, culture and lifestyle
In this instance, ‘environmental’ simply means “outside of the organism”.
Examples include:
An accident may lead to scarring on the body
Eating too much and not leading an active lifestyle will cause weight gain
Being raised in a certain country will cause you to speak a certain language with a certain accent
A plant in the shade of a big tree will grow taller to reach more light

Question 5

What are examples of how genes and environment mix?

Answer 5

Some features vary because of a combination of genetic and environmental causes, for
example:
Tall parents will pass genes to their children for height
Their children have the genetic potential to also be tall
However, if their diet is poor then they will not grow very well
Therefore their environment also has an impact on their height

Question 6

What is meant by natural selection?

Answer 6

In any environment, the individuals that have the best adaptive features are the ones most likely to survive and reproduce

Question 7

How does natural selection work?

Answer 7

Individuals in a species show a range of variation caused by differences in genes
When organisms reproduce, they produce more offspring than the environment is able to support
This leads to competition for food and other resources which results in a ‘struggle for survival’
Individuals with characteristics most suited to the environment have a higher chance of survival and more chances to reproduce
Therefore the alleles resulting in these characteristics are passed to their offspring at a higher rate than those with characteristics less suited to survival
This means that in the next generation, there will be a greater number of individuals with the better adapted variations in characteristics
This theory of natural selection was put forward by Charles Darwin and became known as ‘survival of the fittest’

Question 8

What is Evolution?

Answer 8

Evolution is defined as the change in adaptive features of a population over time as a result of natural selection
The theory of evolution states that all living things have evolved from simple life forms that first developed more than 3 bn years ago

Question 9

How does evolution work?

Answer 9

• Individual organisms within a species can have a wide range of phenotype and genetic variation
• Individuals with characteristics more suited to the environment are more likely to survive to breed successfully
• The alleles that have enabled these individuals to survive are then passed on to the next generation
  If two populations of one species become so different in phenotype that they can no longer interbreed to produce fertile offspring, they have formed two new species

Question 10

Exam Tip on natural selection

Answer 10

Exam Tip
There are many examples of natural selection but they ALL follow the same
sequence described above:
Within a species there is always variation and chance mutation
Some individuals will develop a phenotype (characteristic) that gives
them a survival advantage and this allows them to:
live longer
breed more
be more likely to pass their genes on
Repeated over generations, the ʻmutatedʼ phenotype will become the
norm
Remember, it is the concept you have to understand, not the specific
example.

Question 11

What is selective breeding?

Answer 11

It is the selection of individuals with desirable characteristics and breeding them together

Question 12

How does selective breeding work in animals (and plants)?

Answer 12

Individuals with the characteristics you want are bred together
Offspring that show the desired characteristics are selected and bred together
This process is repeated for many successive generations before you can definitely say you have a ʻnew breedʼ which will reliably show those selected characteristics in all offspring

Question 13

How has selective breeding helped human population to grow?

Answer 13

It has helped the human population to grow by providing increased yields (and increased quality) of plant products (such as rice, maize, fruits and vegetables) and animals products (such as meat, eggs and milk)

Question 14

What are some of the reasons animals are selectively bred?

Answer 14

Animals are commonly selectively bred for various characteristics, including:
- cows, goats and sheep that produce lots of milk or meat
- chickens that lay large eggs
- domestic dogs that have a gentle nature
- sheep with good quality wool
- horses with fine features and a very fast pace

Question 15

Why are plants selectively bred?

Answer 15

Plants are selectively bred by humans for development of many characteristics, including:
disease resistance in food crops
increased crop yield
hardiness to weather conditions (eg. drought tolerance)
better tasting fruits
large or unusual flowers

Question 16

What can be the problems with selective breeding?

Answer 16

• Reduction of alleles in a population because only individuals with chosen alleles are allowed to breed. In stable conditions this is not an issue. However, in case of a problem (for example climate change or a new disease) the lack of variation means that none of the animals in the population might survive.
• Selective breeding can lead to ‘inbreeding’, which limits the size of the gene pool, there is an increased chance of:
  organisms inheriting harmful genetic defects or diseases.

Question 17

What is meant by genetic engineering?

Answer 17

Genetic engineering is changing the genetic material of an organism by removing or altering genes within that organism, or by inserting genes from another organism

Question 18

What are the main steps of genetic engineering?

Answer 18

The main steps in the process of genetic engineering:
- Enzymes are used to isolate (cut out) the required gene
- This gene is inserted into a vector
- The vector is usually a bacterial plasmid (a piece of circular DNA found inside bacterial cells) or a virus
- The vector is used to insert the gene into the required cells of the target organism
- Genes are transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with desired characteristics

Question 19

What are genetically modified crops?

Answer 19

Genetically modified plants are plants that have had foreign DNA inserted into their genome

Question 20

Why are crops genetically modified?

Answer 20

This is usually done to improve food production in some way. Crop plants have been genetically modified to be resistant to diseases or resistant to certain herbicides (so farmers can spray and kill weeds more effectively without killing the crops)
For example:
Tomatoes have been genetically modified to make them grow larger fruit
Wild rice has been genetically modified to produce beta carotene (needed by humans to make vitamin A)

Question 21

How is insuline produced using genetic engineering?

Answer 21

• insuline gene is cut out of DNA by an enzyme
• plasmid taken out of a bacterium and split open by an enzyme
• Insuline gene inserted into plasmid using another enzyme
• The genetically engineered (recombinant) plasmid is inserted into a bacterial cell
• bacterium multiplies
• The genetically engineered bacteria can be placed in a fermenter to reproduce quickly in controlled conditions and make large quantities of the human protein

Question 22

What are the advantages and disadvantages of GM crops?

Answer 22

Advantages:
- Reduced use of chemicals and pesticides which is better for the environment and less time consuming/ cheaper for farmers
- increase yield of crops as they are not competing with weeds or damaged by diseases
Disadvantages:
- Increase cost of seeds means that smaller farmers cannot compete with large multinationals
- Reliance on herbicides which the crops are resistant to. These are made by the same companies making the GM seeds and are more expensive
- Risk that inserted genes are transferred to wild plant (this could for example make weeds resistant to herbicides as well)
- Reduced biodiversity as herbicides kill plants
- Some research has shown that some GM plants do not grow as well as non GM ones

Question 23

What is meant by tissue culture?

Answer 23

It is a more modern form of cloning a plant compared to taking cuttings

Question 24

How does tissue culture work?

Answer 24

• Cells are scraped from the parent plant
• The cells are transferred to a sterile petri dish containing nutrient agar
• Hormones (eg. auxins) are added to encourage plants to grow into small masses of tissue (callus tissue)
• Then using a different mixture of hormones and conditions you can stimulate this cells to form a tiny new plant.

Question 25

What are the advantages of tissue culture ?

Answer 25

The cloning of plants has many important commercial uses.
It allows a variety of a plant with desirable characteristics to be produced:
- cheaply
- with a greater yield (a large number of plants can be produced)
- quickly
- at any time of the year
It can also ensure diseases prevalent in other areas of the world are not imported and spread by ensuring native varieties of plants are produced in large enough quantities to supply demand in one country without importing plants from abroad
Tissue culture can also be an important process in preserving rare plant species

Question 26

How are plants cloned by taking cuttings?

Answer 26

An older and more simple method to clone plants (mainly used by gardeners) is by taking cuttings.
Gardeners take cuttings from good parent plants (eg. those that are healthiest and best-looking) – a section of the parent plant with a new bud is cut off.
These cuttings are then planted and grow into genetically identical versions of the original plant.
Plants cloned by taking cuttings can be produced cheaply and quickly.

Question 27

How does embryo cloning in animals work?

Answer 27

Embryo cloning is achieved in the following way:
- Egg cells from the best cow are artificially fertilised using sperm cells taken from the best bull
- This forms an embryo
- The developing animal embryo is then split apart many times before the cells of the embryo become specialised
- This forms many separate embryos that are genetically identical
- These cloned embryos are then transplanted into host mothers
- The calves born from these host mothers are all genetically identical

Question 28

What are the advantages and disadvantages of embryo cloning in animals?

Answer 28

• Expensive
• Skills needed
  + It is worth it because a good cow can produce 8-10 calves during their life but with cloning around 30 calves can be produced in a year
  + high quality embryos can be transported all around the world, in places where the cattle quality is low

Question 29

How is adult cell cloning performed?

Answer 29

Adult cell cloning is achieved in the following way:
- The nucleus is removed from an unfertilised egg cell
- The nucleus from an adult body cell, such as a skin cell, is inserted into the egg cell
- A very small electric shock stimulates the egg cell to divide (by mitosis) to form an embryo
- These embryo cells contain the same genetic information as the adult skin cell
- When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female (known as the surrogate mother) to continue its development until birth

This process was used to create the first clone (exact genetic copy) of a mammal in 1996
Scientists in Scotland successfully cloned an adult female sheep. The clone was called Dolly

Question 30

Risks and Benefits of cloning

Answer 30

+ Hope to clone medically useful animals when animals that have been genetically engineered to produce useful proteins in their milk are cloned
+ Help save animals from extinction or clone pets or prized animals. BUT some people are not happy with this idea
- Risk of cloning human babies or people might want a clone of themselves
- A lot of plants or animals with identical genes are produced. So the variety in a population is reduced. Hence if a change in the environment happens in the future, the population is less able to survive.

Question 31

What are the benefits of genetic engineering?

Answer 31

• In medicine:
  1. medical research is exploring the possibility of genetic modification to overcome inherited disorders
  2. human insuline and human growth hormone are mass produced using genetically engineered bacteria and fungi
  3. scientists can genetically modify mice so they can mimic human diseases. This is helpful for finding cure for many diseases from cancer to diabetes
• In agriculture:
  1. improve growth rate of plants and animals
  2. increased food values of crops as GM crops have a bigger yield
  3. crops can be engineered to grow well in dry, hot or cold parts of the world
  4. crops can be engineered to produce plants that make their own pesticides or be resistant to herbicides used to control weeds

Question 32

What are concerns around genetic engineering?

Answer 32

• It is still a new science and no one knows what the long term effects can be (for example, may be insects can become pesticide resistant of they eat constantly pestice resistant plants)
• Some peole have concerns on their impact on human health. However, we normally eat organisms with many different types of DNA every day so our enzymes should be able to break down and deal with any extra genes
• Genes from GM plants and animals might spread into wildlife. GM crops were originally made infertile. If the infertility gene spread into wildlife i could have disastrous effects
• Fears about engineering humans, ethical concerns, for example kids with desired characteristics

Question 33

Positives of GM crops

Answer 33

• they are seen as the only way to feed the growing human population and cope with global warming