B6.2- Variation and Evolution.

Question 1

How is genetic variation caused?

List some characteristics determined only by genes?

Answer 1

• It comes from the crossing over of chromosomes which leads to genetic variation.
• An organism’s characteristics are determined by the genes inherited from their parents and the genes are passed on in sex cells( gametes) from which the offspring develop and genetic variation is caused when most offspring inherit genes from their mother and some from their father; the mixing of the chromosomes and genes leads to genetic variation.
• Some characteristics determined only be genes could be eye colour, blood group, and inherited disorders.

Question 2

How do identical twins come to be?

Answer 2

Identical twins are from the same fertilised egg and divide to form 2 genetically identical embryos.

Question 3

How can characteristics be influenced by the environment? Give examples.

Answer 3

-The environment and the conditions that organisms live and grow in also causes differences between species and this is called environmental variation.

For eg, a plant growing in plenty of sunlight will be luscious and green but the same identical plant grown in darkness would grow tall and have yellow leads and this is due to environmental variation.

-Variation can be affected by nurture which is environmental factors for eg scars, accents

Question 4

Give characteristics that are both influenced by the genetic and environment?

Answer 4

• Body weight, height, skin colour.

- Max height can be determined by genes but whether it actually reaches and grows that tall depends on its environment.

Question 5

First, determine what is a mutation; how often does it occur?

How can mutation lead to variation?

Answer 5

-Mutations are changes to the sequence of bases in DNA and they can lead to changes in the protein that gene codes for. Most mutations will have no effect on the protein the gene codes and hence have no effect on the organism’s phenotype.
Some may have a small influence on phenotype so alter characteristics slightly but although it’s v rare, mutations can result in a new phenotype being seen in a species.

-If the enviro changes, the new phenotype makes an individual more suited to a new environment, it can become common throughout the species relatively quickly by natural selection.

Question 6

What is the theory of evolution?

How does it relate to ‘survival of the fittest’?

Answer 6

States that all of today’s species have evolved from simple life forms that first started to develop over 3 billion years ago.

-‘Survival of the fittest’ concluded that the organisms with the most suitable characteristics for the environment would be more successful competitors and would be more likely to survive due to having an advantage. The successful organisms that survive are more likely to reproduce and pass on the genes for the characteristics that make them successful to their offspring. The organisms that are less adapted will be less likely to survive and reproduce so they will be less likely to pass on the genes to the next generation. Over time, the allele frequency will increase

Question 7

When answering a 6 marker on Natural selection, what are the 6 points to consider?

Answer 7

1) Variation occurs so natural selection occurs.
2) Competition due to the environment or surroundings.
3) ‘Survival of the fittest’ as variation will give the species an advantage over others.
4) Reproduction- reproduce to pass on the useful alleles to the offspring.
5) Over time, the allele frequency would increase as the offspring with the useful, desired genes would reproduce.
5) Speciation can also occur if a species evolved from another which would help create a new frequency.

Question 8

How does a mouse get to have good hearing?

Answer 8

A mouse gets to have good hearing due to variation which leads to them having an advantage in the competition by being able to hear predators. This will allow them to survive in the survival of the fittest as variation gives the mouse an advantage over others. They will then reproduce to pass the useful desired alleles to the offspring and overtime, the allele frequency will increase as the offspring will then further reproduce to pass on the desired alleles so on and so forth.

Question 9

What is the development of new species called?

Answer 9

• Development of new species is called speciation and over a long period of time, the phenotype of an organism can change so much that a completely new species is formed.
• Speciation happens when the populations of the same species change enough to become reproductively isolates and they can’t interbreed to produce fertile offspring.

Question 10

How can extinction occur?(5)

Answer 10

Extinction can occur:

• the environment changes too quickly.
• new predator kills them all.
• new disease.
• they can’t compete with another new species for food.
• a catastrophic event that kills them all such as a volcanic explosion.

Question 11

Define selective breeding.

Answer 11

Selective breeding is when humans artifically breed selective plants and animals for desired characteristic.

Question 12

Why may humans selectively breed plants and animals? (4)

Answer 12

They may selectively breed plants and animals to have features such as:

• disease resistance.
• dogs with good, gentle temperament.
• animals produce more milk or meat.
• decorative plants with big or unsual flowers.

Question 13

Describe the process of selective breeding?

Answer 13

1) From the exisiting stock, select the desirable trait or characteristics.
2) Breed them with each other.
3) Select the best of the offspring with the desirable traits and breed them together.
4) Continue this process over several generations anf the desirable trait gets stronger and stronger so eventually, overtime, all the offspring will have the characteristic.

Question 14

How can selective breeding be used in agriculture;

• Wheat
• Cows
• Chickens.

Answer 14

• Wheat: large SA available to give a higher yiled, bred them to be shorter so they are heavier at the top and don’t fall, larger ear so there is more position for more grain.
• Cows: quality of meat- docile cows, high yield of milk, high yield of meat.
• Chickens- breed them to have less feathers, breed for quality and yield of meat, high yield and consistency of eggs.

Question 15

Main drawbacks of selective breeding? (4)

Answer 15

• Reduces the gene pool and the number of different alleles in a population as the farmer keeps breeding from the best animals or plants which are all closesly related- inbreeding.
• Inbreeding can cause healthy problems because more of a chance of organisms inheriting harmful genetic defects when the gene pool is limited
• Serious problem is new disease- lack of variation as all sstock are closely related to each other.
• dependancy on humans- creates docile animals.

Question 16

Descrive how to breed chickens for high egg yield? (4)

Answer 16

1) select desirable traits from the female chicken that produces high yield of eggs and find a male chicken whose mother produces a large number of eggs.
2) breed the chickens together.
3) Select the best femae offspring that have a high yiled of eggs and a male whose mother produced a large yield off eggs and breed them together.
4) Continue this process overtime so all the offspring of the chicken will have the characteristic of producing a high yiled of eggs.

Question 17

What is genetic engineering?

Answer 17

Genetic engineering is modifying or alternating the genetic material of an organism. The gene for a desirable charcteristic is cut out of one organism and transferred to the genetic material in the cells of another organism.

Question 18

Describe the steps to genetic engineering. (6)

When is the gene transferred? when in plants?

Answer 18

1) Choose a gene( section of the code).
2) Remove the gene from the organism and use restrictive enzymes to cut only the desirable gene.
3) The recombinant gene is transferred into a vector and the vector is either a plasmid or viruses.
4) Use ligase to ‘stick’ the DNA strand back together.
5) The vector is then used to insert the genes into the required cells AND THIS HAPPENS IN THE EARLY STAGE OF AN ORGANISM’S LIFE.
6) Check the gene works in the transgenic organism.

The transfer of the gene is carried out when the organism recieving the gene is at an early stage of development(eg, egg or embryo) and this means that it allows the organism to develop with the characteristic coded for by the gene. In plants, the desired genes are often inserted into the meristem cells which are then used to produce identical clones of the genetically modified plant.

Question 19

Give examples of genetic engineering?(3)

Answer 19

-Bacteria have been GM to produce human insulin that can be used to treat diabetes.
- GM cropes have genes modified eg. to improve the size and quality of their fruit or make them resistane to disease, insects and herbicides
- Sheep have been GM to produce subst like drugs in milk to treat human disease.
-

Question 20

How can genetic engineering offer treatment for genetic disorders. (2)

Answer 20

-Using viral vectors as viruses can be used to transfer the corect desirable gene in the genome to cure a disease or fix a faulty gene and the body cellss with chance to incorporate in the genome.
-Viral vectors can be used to cure diseases such as cystic fibrosis or replace and fix faulty genes.
However they are still a work in progress

Question 21

What are the advantages and disadvantages of genetic engineering?

Answer 21

Adv- increase crop yield, GM crops could be engineered to contain the nutrient that’s missing from the people’s diets and can help improve the healthiness of different food and diet.

Disadv: make farming more expensive as farmers have to repurchase the seeds from the companies and if unable to do that= famine,

• cross polinate GM crops with non GM crops,
• raised health issues of mixing of genes, not fully understand the effects of eating them on human health

Question 22

What is Cloning?

Answer 22

A clone is an individual that has been produced asexually and is genetically identical to the parent.

Question 23

How can you clone plants through cuttings? (2)

Answer 23

It’s a form of artificial asexual reproduction

1) Take a cutting of the plant where we remove part of the plant and place it into the soil.
2) This process relies on meristem tissue and the plants produced will be genetically identical.

Question 24

What are the advantages of cloning plants? (4)

Answer 24

• Easy to do and easy process.
• Genetically identical clone to plant.
• Cheap.
• Make a large number from 1 plants.

Question 25

What are the disadvantages of cloning plants? (4)

Answer 25

• they will be more susceptible to disease killing the lot.
• smaller gene pool-wouldn’t be able to adapt to new surroundings as there is no variation.
• risk of genetic disorder or mutation and all can be susceptible to mutation
• limited to the size of the plant.

Question 26

Describe the process of tissue culture.

Answer 26

This is where a small group of cells taken from part of a plant to grow identical new plants. Grow it on A GROWTH MEDIUM WITH HORMONES AND THEY GROW INTO NEW PLANTS- CLONES OF THE PARENT PLANT. TISSUE CULTURE IS USED BY SCIENTISTS TO PRESERVE RARE PLANTS THAT ARE HARD TO REPRODUCE NATURALLY AND BY PLANT NURSERIES TO PRODUCE STOCK QUICKLY.

Question 27

(5) Adv and (4) Disadv of tissue culture?

Answer 27

Adv:- huge yield from a small sample as it can be used for endangered species.

• the technique can be used for a very expensive plant.
• allows to do a process that is seasonal and do all year round.
• only require a small sample.
• aseptic technique stops diseases.

Disadv:

• require specialist training and equipment.
• an expensive technique.
• more sussceptivle to the same disease.
• requires aseptic technique.

Question 28

What are the 2 forms of animal cloning?

Answer 28

1) Embryo transplant.

2) Adult stem cell cloning.

Question 29

Describe the process of embryo cloning? (5)

Answer 29

1) Remove egg and sperm from individuals we select.
2) In a petri dish, combine egg and sperm to form an embryo AND THE SPERM WILL ARTIFICIALLY FERTILISE THE EGG CELL.
3) Split the embryo so each new set of cells can develop.
4) Transplant into the surrogate.
5) All offspring will be identical to each other.

Question 30

What are the adv for embryo cloning? (6)

Answer 30

Adv:

• all genetically identical to each other.
• make many offspring from a small sample and this can be a benefit to endangered species.
• reproduce from an animal without letting them breed and it reduces the risk for mother.
• allows the farmer to produce offspring from an existing stock.
• select gender.
• genetically screen from beforehand.

Question 31

What are the disadv for embryo cloning? (7)

Answer 31

• combination of genetic material produces variation in offspring.
• ethical.
• more expensive.
• smaller gene pool.
• lower success rate.
• requires specialist.
• done in aseptic technique

Question 32

What is the process of adult stem cell cloning? (5)

Answer 32

1) The adult that is to be cloned, you remove the nucleus from a body cell.
2) You have a female donor animal and select an egg from the donor and remove the nucleus.
3) Combine the egg and the nucleus and give it an electric shock.
4) Embryo will develop into a ball of cells.
5) The embryo is implanted in a surrogate animal and the cells of the embryo contain the same genetic information as the adult skin cells.

Question 33

1 bIG Adv(2) and disadv (5) of adult stem cell cloning?

Answer 33

Adv:

• animals that have been genetically engineered to produce useful proteins can be cloned and this would give us a good way of producing large numbers of cloned, medically useful animals.
• help save animals from extinction.

Disadv

• process is v expensive and time consuming.
• need a lot of donor eggs.
• low successful rates.
• small gene pool so higher risk to genetic disorders
• clones are more likely to have damaged cells as they may have old cells or the DNA can have mutation which can lead to a shorter life spam.

Question 34

Emrbyo transplant vs ASC? Max 3 points for each.

Answer 34

-Embryo transplant- creates more identical clones from one single embryo, less invasive and exact clones are produced
whereas
-ASC- could bring back extinct species and produces genetic clones of an existing animal.

Question 35

Why is plant cloning easier than animal cloning?

Answer 35

It’s a much cheaper process and requires simpler equipment and less expertise. Plant cloning can make a large number of plants from a small sample as it’s easier to obtain stem cells from plants. There’s also less of an ethical problem with plant cloning.
-Success rates are higher and no other organism is involved whereas in embryo and ASC are dependant on an organism whereas plant cloning can sustain itself.

Question 36

Advantages of genetic engineering in agriculture? (4)

Answer 36

1) Improved growth rates of plants and animals.
2) GM crops have a much bigger yield than ordinary crops.
3) Crops can be designed to grow in specific climates.
4) Crops can be engineered to be resistant to pesticides or diseases.