Topic 6 - Inheritance, Variation and Evolution Flashcards
(146 cards)
1
Q
What does DNA stand for?
A
Deoxyribonucleic acid.
2
Q
What is DNA?
A
The chemical that all of the genetic material in a cell is made up from. It contains coded information, that determines what inherited charcteristics you have.
3
Q
Where is DNA found?
A
In the nucleus of animal and plant cells, in really long structures called chromosomes.
4
Q
How are chromosomes normally found?
A
In pairs.
5
Q
What is DNA made up of?
A
Polymer - made up of two strands coiled together in the shape of a double helix.
6
Q
What is a gene?
A
A small section of DNA found on a chromosone.
7
Q
What does each gene code for?
A
A particular sequence of amino acids which are put together to make a specific protein. Only 20 amino acids are used, but they make up thousands of different proteins. They tell cells what order to put the amino acids in.
8
Q
What determines what proteins the cell produces?
A
DNA and genes.
9
Q
What does genome mean?
A
The entire set of genetic material in an organism.
10
Q
Why is understanding the human genome important?
A
- identify genes linked to types of diseases
- what genes link to inherited diseases which could help develop effective treatments.
- trace the migration of populations - investigate the difference in genome to work out when new populations split off in a different direction and what route they took.
11
Q
What are DNA strands?
A
Polymers made up of lots of repeating units called nucleotides.
12
Q
What does each nucleotide consist of?
A
One sugar molecule, one phosphate molecule and one ‘base’.
13
Q
What do the sugar and phosphate molecules in the nucleotides form?
A
A ‘backbone’ to the DNA strands. The sugar and phosphate molecule alternate. One of four different bases joins to each sugar.
14
Q
What is complementary base sharing?
A
A always pairs up with T.
C always pairs up with G.
15
Q
What decides the order of amino acids in a protein?
A
The order of bases in a gene.
16
Q
What is each amino acid coded by?
A
A sequence of three bases in the gene.
17
Q
What do the proteins amino acids make when joined together depend on?
A
The order of the genes bases.
18
Q
What do the parts of DNA that don’t code for proteins do?
A
Switch genes on and off, so they can control whether or not a gene is expressed.
19
Q
Where a proteins made?
A
In the cell cytoplasm on tiny structures called ribosomes.
20
Q
How are proteins made?
A
Ribosomes use the code in the DNA.
21
Q
How is the code moved from the DNA to the ribosome?
A
Through a molecule called mRNA - which is made by copying the code from DNA. It acts as a messenger between the DNA and the ribosome - carries the code between the two.
22
Q
How are the correct amino acids brought to the ribosome?
A
In the correct order by carrier molecules.
23
Q
What happens when a chain of amino acids have been assembled?
A
It folds into a unique shape which allows the protein to perform the task it’s meant to.
24
Q
Give examples of proteins.
A
- Enzymes - act as biological catalysts to speed up chemical reactions in the body.
- Hormones - used to carry messages around the body.
- Structural proteins - are physically strong. eg. collagen strengthens ligaments and cartilage.
25
What is a mutation?
A random change in an organism's DNA.
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Can mutations be inherited?
Yes.
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What is the chance of a mutation increased by?
Exposure to certain substances or some types of radiation.
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How do mutations affect DNA?
They change the sequence of the DNA bases in a gene, which produces a genetic varient.
29
Why can mutations to a gene sometimes lead to changes in the protein that it codes for?
As the sequence of DNA bases codes for the sequence of amino acids that made up a protein and mutations change the sequence.
30
Why do most mutations have very little or no effet on the protein.
They may only change it to such a small extent that its function or appearance is unaffected. hi xoxo
31
Why can some mutations seriously affect a protein?
They may code for an altered protein with a change in its shape which could affect its abiltiy to perform its function.
32
Give an example of how a mutation can affect a proteins function.
1. If the shape of an enzyme's active site is changed, its substrate may no longer be able to find it.
2. Structural proteins like collagen could lose their strength if their shape is changed, making them useless at providing strucuture and support.
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What can happen if there is a mutation in non coding DNA?
It can alter how the gene is expressed.
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What are three different types of mutation?
Insertions, deletions and substitutions.
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What are insertions?
Where a new base is inserted into the DNA base sequence where it shouldn't be. This changes the way the groups of three bases are read which can change the amino acid they code for. This an change more than one amino acid as they have a knock on effect on the bases further on in the sequence.
36
What are deletions?
When a random base is deleted from the DNA base sequence. They change the way that the base sequence is 'read' and have a knock on effecr fown the sequence.
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What are substitution mutations?
When a random base in the DNA base sequence is changed to a different base.
38
What is sexual reproduction?
Where genetic information from two organisms is combined to produce offspring which are genetically different to either parent.
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What do the mother and father produce in sexual reproduction/
Gametes (by meiosis), eg. egg and sperm in animals.
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How many chromosomes does each gamete contain in humans?
23 chromosomes - half the number in a normal cell.
| They have one of each chromosome instead of two.
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What is fertilisation?
When the egg and sperm cells fuse together to form a cell with the full number of chromosomes.
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What does sexual reproduction involve?
The fusion of male and female gametes. Becuase there are two parents, the offspring contains a mixture of their parents' genes.
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Why do offspring inherit features from both parents?
It has recieved a mixture of chromosomes from its mum and dad.
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What produces variation in the offspring?
The mixture of genetic information.
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Can flowing plants reproduce via sexual reproduction?
Yes. They have egg cells and pollen.
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What is asexual reproduction?
When there's only one parent so the offspring are genetically identical to that parent.
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Does asexual reproduction happen via meiosis or mitosis?
Mitosis - an ordinary cell makes new cells by diving into two.
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Why are cells produced via asexual reproduction a clone?
It happens by mitosis so the new cell has exactly the same genetic information as the parent cell.
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What is the definiton of asexual reproduction?
There is only one parent. There is no fusion of gametes, no mixing of chromosomes and no genetic variation between parent and offspring, The offspring are genetically identical to the parent - they're clones.
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What reproduces asexually?
Bacteria, some plants and some animals.
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How are gametes produced?
Cell division by mitosis. The process involves two cell divisions, and in humans, only happens in reproductive organs (ovaries and testes).
52
Describe the process of Meiosis.
1. Before the cells start to divide, it duplicated its genetic information, forming two armed chromosomes- one arm of each chromosome is an exact copy of the other arm. After replication, the chromosomes rearrange themselves into pairs.
2. In the first division in meiosis the chromosome pairs line up in the centre of the cell.
3. The pairs are then pulled apart so each new cell only has one copy of each chromosome.
4. In the second division, the chromosomes line up again in the centre of the cell. The arms of the chromosomes are pulled apart.
5. You get four gametes, each with only a single set of chromosomes in it. Each gamete is genetically different from the others because the chromosomes all get shuffled up during meiosis and each gamete only gets half of them, at random.
53
How are whole organisms made by two gametes?
After two gametes have fused during fertilisation, the new cell divides by mitosis to make a copy of itself. Mitosis repeats many times to produce lots of new cells in an embryo. As the embryo develops, these cells start to differentiate into the different types of specialised cell that make up a whole organism.
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What is an advantage of sexual reproduction?
Offspring from sexual reproduction have a mixture of two sets of chromosomes. Genes are inherited from both parents, producing variation. - survival advantage.
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Why is variation an advantage of sexual reproduction?
Variation increases the chance of a species surviving a change in the environment. A change in environment could kill some individuals, but variation will have led to some of the offspring to survive in the new environement. They have a survival advantage. These individuals are more likely to pass on their characteristics - natural selection.
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How can we speed up natural selection?
Using selective breeding. We can produce animals with desirable characteristics.
Individuals with desirable characteristics are bred to produce offspring that have the same characteristics. This means we can increase food production...
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What are advantages of asexual reproduction?
Only needs to be one parent so uses less energy than sexual reproduction, because organisms don't need to find a mate. So is also faster.
Many identical offspring can be produced in favourable conditions.
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Which organisms can reproduce both sexually and asexually?
Malaria, fungus and plants.
59
Describe how malaria can reproduce.
Caused by a parasite that is spread by mosquitoes. When a mosquito carrying the parasite bites a human, the parasite can be transferred to the human. The parasite reproduces sexually when in the mosquito and asexually when in the human host.
60
Describe how fungi reproduce.
The species can release spores which can become new fungi when they land in a suitable place. Spores can be produced sexually and asexually.
Asexually produced spores form fungi that are genetically identical to the parent fungus.
Sexually produced spores introduce variation and are often produced in response to an unfavourable change in the environment, increasing the chance that the population will survive that change.
61
Describe how many species of plant reproduce.
Many plants can produce seeds sexually and asexually.
Asexual reproduction- Strawberry plants produce 'runners', which are stems that grow horizontally on the surface of the soil away from the plant. At various points on the runner, a new strawberry plant forms that is genetically identical to the original plant. Another example is plants that grown bulbs. New bulbs can form from the main bulb and divide off. Each new bulb can grow into a new identical plant.
62
How many pairs of chromosomes are in every human body cell?
23 pairs.
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What are 22 of the chromosomes?
Matched pairs just controlling characteristics.
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What is the 23rd chromosome pair?
Labelled XX or XY. They are the chromosome that decide your sex.
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What chromosome do males have?
X and Y - the Y chromosome causes male characteristics.
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What chromosomes do females have?
Two X chromosomes - the XX combination allows female characteristics to develop.
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What happens when making sperm?
The X and Y chromosomes are drawn apart in the first division in meiosis. There is a 50% chance each chromosome gets an X chromosome and 50% chance it's a Y.
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How can you find the probability of getting a boy or girl?
By drawing a genetic diagram.
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What are genetic diagrams?
Models that are used to show all thge possible genetic outcomes when you cross together different genes or chromosomes.
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What is a type of genetic diagram besides a Punnett square?
A diagram with the parents at the top and criss cross lines showing all the possible ways/ combinations of the offspring.
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What are most characteristics controlled by?
Several genes interacting.
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What characteristics are controlled by a single gene?
Mouse fur colour, red- green colour blindness.
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How do genes exist?
In different versions called alleles.
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What is an allele?
You have two versions of every gene in the body - one on each chromosome pair. An allele is a different version of a gene.
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What does homozygous mean?
The organism has two alleles that are the same for a particular gene.
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What does heterozygous mean?
The organism have two alleles for a particular gene that are different.
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What is a dominant allele?
The allele for the characteristic that is shown. Shown by using a capital letter.
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What is a recessive allele?
The allele for the characteristic that is not shown. Shown by using a lowercase letter.
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What must happen for an organism to display recessive characteristics?
Both its allels must be recessive.
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What must happen for an organism to display dominant characteristics?
They can either be CC or Cc, since the dominant allele overrules the recessive one if the organism is heterozygous.
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What is your genotype?
The combination of alleles you have.
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What is your phenotype?
Characteristics (alleles work at a molecular level to determine what characteristics you have).
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What do genetic diagrams tell you/ don't tell you?
Only tell you probabilities, not definitely what will happen.
84
What would you expect the alleles of the parents to be when there is a ratio of 1:1.
Hh and hh. Heterozygous and homozygous recessive.
85
What are the alleles for someone who is affected by cystic fybrosis?
ff.
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What are the alleles for someone who is unaffected by cystic fybrosis but still a carrier?
Ff.
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What are the alleles of someone unaffected by cystic fybrosis and not carriers?
FF.
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What is cystic fybrosis?
A genetic disorder of the cell membrane resulting in the body producing a lot of thick sticky mucus in the air passages and in the pancreas.
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What allele causes cystic fybrosis?
Recessive allele 'f'.
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Why are people with only one copy of the cystic fybrosis allele unnaffected? What are these people known as?
It is recessive. Known as carriers.
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What is polydactyly?
A genetic disorder where a baby is born with extra fingers or toes.
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Is polydactyly life threatening?
No - doesn't usually cause any other problems.
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What allele is polydactyly caused by?
Dominant allele 'D', so can be inherited if just one parent carries the defective allele.
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Will the parent who has the defective allele be affected?
Yes. The allele is dominant.
95
How are many genetic disorders detected before birth?
During IVF, embroyos are fertilised in the lab before being implanted. It is possible to remove a cell from each embroyo and analyse its genes before being implanted.
It is also possible to get DNA from the embryo in the womb to test for disorders.
96
Why are people against embryonic screening?
- It implies that people with genetic problems are undesirable - could increas prejudice.
- May come to a point where everyone wants to screen their embryos so they can pick the most 'desirable' ones.
- Screening is expensive.
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What are people in favour of embryonic screening?
- It will help to stop people suffering.
- Treating disorders cost the Government a lot of money.
- There are laws to stop it going too far.
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What are the two types of variation?
Genetic and environmental variation.
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What causes genetic varation?
Combining genes from two parents. - not two of the species are identical
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What characteristics are only determined by genes?
Eye colour, blood group and inherited disorders
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What is environmental variation?
The environment, including conditions that organisms live and grow in, causes differences between members of the same species.
102
What is an example of environmental variation in plants?
A plant grown in sunlight would be lucious and green but the same plant grown in darkness would grow tall and spindly and have yellow leaves.
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What are characteristic examples that are a mixture of both environmental and genetic variation?
Weight, height, skin colour, condition of teeth, academic or athletic prowess.
104
What is the maximum height that an animal or plant could grow to determined by?
Genes - however whether it actually grows that tall depends on its environment.
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Why do most mutations have no/ very little effect on the organism's phenotype?
Most mutations have no effect on the protein the gene codes for. They may have a small influence on the phenotype so may only alter characteristics slightly.
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Why can mutations introduce variation?
If the environment changes, and the new phenotype makes an individual more suited to the new environment, it can become common throughout the species relatively quickly by natural selection.
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What is the theory of evolution?
All of today's species have evolved from simple life forms that first started to develop over three billion years ago.
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What is phenotypic variation?
Organisms in a species show wide variation in their characteristics.
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What is 'survival of the fittest'?
Organisms with the most suitable characteristics for the environment would be more successful competitors and would be more likely to survive.
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Describe how species evolve over time?
Organisms with the most suitable characteristics for the environment would be more successful competitors and would be more likely to survive. These organisms are more likely to reproduce and pass on the genes to their offspring. Organisms that are less well adapted are less likely to survive and reproduce, so less likely to pass their genes to the next generation. Over time, these beneficial characteristics become more common in the population and the species changes.
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Why wasn't Dawins theory of evolution perfect?
The relevant scientific knowledge was not available at the time so he couldn't give a good explanation.
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What is speciation?
Over a long period of time, the phenotype of organisms can change so much because of natural selection that a completely new species is formed.
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Why does speciation happen?
When populations of the same species change enough to become reproductively isolated so they cant' interbreed to produce fertile offspring.
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What is meant by extinct?
A species does not exist anymore.
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Why may species become extinct?
1. Environment changes too quickly.
2. New predator kills them all.
3. A new disease kills them all.
4. They can't compete with another (new) species for food.
5. A catastrophic event happens killing them all.
116
What was Dawin's theory controversal?
Went against common religious beliefs about how life on earth developed.
He couldn't explain why the new, useful characteristics appeared or how they were passed on, as he didn't know about genes and mutations.
There was not enough scientific evidene to convince many scientists.
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What was Lamarck's hypotheses?
Changes that an organism acquires during its lifetime will be passed on to its offspring. If a characteristic was used a lot by an organism it would become more developed during its lifetime and the offspring would inherit these acquired characteristics.
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Why is Dawin's theory now accepted?
Discovery of genetics, fossils, antibiotic resistant bacteria and natural selection.
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How are plants cloned by tissue culture?
A few plant cells are put into a growth medium with hormones and they grow into new plants - clones of the parent plant.
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What are advantages of growing plant clones in a growth medium?
Can be made very quickly, in very little space and be grown all year.
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Why do scientists and plant nurseries use tissue culture?
To preserve rare plants that are hard to reproduce naturally and by plant nurseries to produce lots of stock quickly.
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How are plants cloned by cuttings?
Gardeners can take cuttings from good parent plants, and then plant them to produce genetically identical clones of the parent plant.
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What are advantages of growing plant clones by cuttings?
Plants can be produced quickly and cheaply. This is an older, simpler method than tissue culture.
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How can farmers produce cloned offspring of their bulls/ cows?
Using embryo transplants.
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How do embryo transplants work?
- Sperm cells are taken from the bull and egg cells are taken from the cow. The sperm is used to artificially fertilise the egg cell. The embryo that develops is then split many times to form clones before any cells become specialised.
- The cloned embryos can then be implanted into lots of other cows where they grow into baby calves.
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What is an advantage of embryo transplants?
Hundereds of ideal offspring can be produced every year from the best bull and cow.
127
Describe the process of adult cell cloning.
- Remove the nucleus from an unfertilised egg cell. The nucleus is then removed from an adult body cell and is inserted into the 'empty' egg cell.
- The egg cell is stimulated with an electric show causing it to divide.
- When the embryo is a ball of cells it's implanted into the womb of an adult female. It grows into a genetically identical copy of the original adult body cell as it has the same genetic information.
128
How was Dolly the sheep created?
By adult cell cloning.
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What are advantages of cloning?
- Quickly gets you 'ideal' offspring.
- Study of animal clones leads to greater understanding of the development of the embryo, and of ageing and age related disorders.
- Help preserve endangered species.
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What are disadvantages of cloning?
- You get a 'reduced gene pool' so there are fewer alleles in a population. Since the population is so closely related, a new disease could wipe them all out as there may be no allele giving resistance to it.
- Cloned animals may not be as healthy as the normal ones.
- Possibility of human cloning in the future.
131
What are fossils?
The remains of organisms from many thousands of years ago, which are found in rocks. They provide the evidence that organisms lived ages ago.
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What can fossils tell us?
How much or how little organisms have evolved over time.
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What are the three ways fossils form in rocks?
Gradual replacement by minerals, casts/ impressions and presevation in places where no decay happens.
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How are fossils formed from gradual replacement by minerals?
1. Things like teeth, shells, bones, which don't decay easily can last a long time when buried.
2. They are eventually replaced by minerals as they decay, forming a rock-like substance shaped like the original hard part.
3. The surrounding sediments also turn to rock, but the fossil stays distinct inside the rock and eventually someone digs it up.
135
How are fossils formed by casts and impressions?
Fossils are formed when an organism is buried in soft materials like clay. The clay layer hardens around it and the organism decays, leaving a cast of itself.
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What are examples of casts and impressions?
An animals burrow or plant's roots can be preserved in casts.
Footprints can be pressed into materials when soft leaving an impression when it hardens.
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How are fossils formed from presevation?
1. In amber and tar pits there is no oxygem or moisture so decay microbes can't suvive.
2. In glaciers it is too cold for the decay microbes to work.
3. Peat bogs are too acidic for decay microbes.
138
Why is the fossil record incomplete?
- Many early life forms were soft bodied and soft tisue tends to decay away completely.
- Fossils formed millions of years ago may have been destroyed by geological activity.
139
What happens when bacteria develops random mutations in their DNA?
Changes in the bacteria's characteristics, eg. being less affected by a particular antibiotic. This can lead to anti-biotic resistant strains forming as the gene for antibiotic resistance becomes more common in a population.
140
Why can antibiotic strains of bacteria evolve quite quickly?
Rapid at reproducing.
141
Why is antibiotic resistance a big advantage, for the bacteria?
It's better able to survive, even in a host who's being treated to get rid of the infection, so it lives for longer and reproduces many more times. This increases the population size of the resistant strain.
142
Why are antibiotic strains a problem for people who have been infected?
They aren't immune to the new strain and there is no effective treatement, so infections can spread easily from person to person.
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What is a superbug?
One that is resistant to most known antibiotics.
144
What is an example of a relatively common superbug?
MRSA - often infects people in hospitals and can be fatal if it eneters their bloodstream.
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Why is the problem of antibiotic resistance getting worse?
- Overuse and inappropriate use of antibiotics. eg. doctors prescribing them for non-serious conditions or infections caused by viruses.
- Not taking the full course - you are supposed to make sure all the bacteria is destroyed so none are left to mutate and develop strains.
146
Why are antibiotics used in farming? How can this lead to resistance?
To prevent animals from becoming ill and make them grow faster. Antibiotic-resistant bacteria in animals can then spread to humans, eg. during meat preperation/ comsumption.
