T6: Inheritance, variation, evolution Flashcards
What is DNA?
The genetic material in the nucleus of a cell is composed of a chemical called DNA.
What does DNA contain?
DNA contains coded information. What is in your DNA determines what characteristics you have.
Where is DNA contained/ found?
- DNA is found in the nucleus of animals and plant cells.
- the DNA is contained in structures called chromosomes.
How are chromosomes found?
Chromosomes normally comes in pairs.
What is DNA’s in terms of its structure?
DNA is a polymer made up of two strands (coiled together) forming a double helix.
What is a gene?
A gene is a small section of DNA found on a chromosome.
What does each gene do?
Each gene codes for a particular sequence of amino acids, to make a specific protein. (genes simply tell cells in what order to put the amino acids together)
How many amino acids have been used overall?
Only 20 amino acids are used but they make up thousands of different proteins.
What does DNA do in terms of proteins?
DNA also determines what proteins the cells produces e.g. haemoglobin, keratin. This in turn determines what type of cell it is.
What is the genome?
The genome of an organism is the entire genetic material of that organism.
Why is understanding the human importance really important for science and medicine?
1) it allows scientists to IDENTIFY GENES that are linked to different types of disease.
2) understanding and developing effective treatment of inherited disorders.
3) use in tracing human migration patterns from the past.
What are DNA strands?
polymers made up of lots of repeating units called nucleotides.
The long strands of DNA consist of alternating sugar and phosphate sections. Attached to each sugar is one of the four bases.
The DNA polymer is made up of repeating nucleotide units.
What does each nucleotide consist of?
a sugar, a phosphate group and one ‘base’.
- The sugar and phosphate groups in the nucleotides form a ‘backbone’ to the DNA strands. The sugar and phosphate groups alternate/
How many different bases are there and what are they?
4 different bases, A, T, C or G.
One of the bases joins to each sugar.
What does each base link to?
a base on the opposite stand in the helix.
What is the complementary base pairing?
In the complementary strands a C is always linked to a G on the opposite strand and a T to an A.
What is each amino acid coded for?
A sequence of three bases is the code for a particular amino acid.
(The amino acids are joined together to form various proteins, depending on the order of the gene’s bases)
What does the order of bases control?
The order of bases controls the order in which amino acids are assembled to produce a particular protein.
What do the parts of DNA that don’t control for proteins do?
Some of the non coding parts switch genes on and off, so they control whether or not a gene is expressed.
What does mRNA do?
1) Proteins are made in the cell cytoplasm on tiny structure called ribosomes.
2) To make proteins, ribosomes use the code in the DNA. DNA found in the cell nucleus and can’t move out of it because it is really big. So the cell needs to get the code from the DNA to the ribosomes.
3) This is done using a molecule called mRNA; which is made by copying the code from DNA. The mRNA acts as a messenger between the DNA and the ribosomes- it carries the code between the 2.
4) The correct amino acids are brought to the ribosomes in the correct order by carrier molecules.
What allows a protein to perform the task it is meant to do?
When the protein chain is complete it folds up to form a unique shape. This unique shape enables the proteins to do their job as enzymes, hormones or forming structures in the body such as collagen.
What are 3 examples of protein?
1) ENZYME: act as biological catalysts to speed up chemical reactions in the body.
2) HORMONES: used to carry messages around the body.
3) STRUCTURAL PROTEINS: are physically strong
Give an example of a structural protein and its function.
Collagen is a structural protein that strengthens connective tissues (like ligaments + cartilage).
What is a mutation?
A mutation is a random change in an organism’s DNA. They can sometimes be inherited.
How often do mutations occur?
Mutations occur continuously but they can occur spontaneously e.g. when a chromosome isn’t quite replicated properly.
How can the chance of a mutation increase?
exposure to certain substances or some types of radiation.
What do mutations change?
Mutations change the sequence of the DNA bases in gene, which produces a genetic variant.
Why do mutations sometimes lead to changes in the protein it codes for?
As the sequence of DNA bases codes for the sequence of amino acids that make up a protein, mutations can sometimes lead to changes in the protein it codes for.
What is the effect of most mutations?
Most do not alter the protein, or only alter it slightly so that its appearance or function is not changed.
How can mutations be dangerous?
- Some mutations can seriously affect a protein. Sometimes, the mutation will code for an altered protein with a change in its shape. This can affect its ability to perform its function e.g.
1) if the shape of an enzyme’s active site is changed, its substrate may no longer be able to bind to it.
2) Structural proteins like collagen could lose their strength if their shape is changed, making them pretty useless at providing structure and support.
What happens if there is a mutation in a noncoding DNA?
it can alter how the genes are expressed.
What are the 3 types of mutations?
- Insertions
- Deletions
- Substitutions
What are insertions?
Insertions are where a new base is inserted into the DNA base sequence where it shouldn’t be
What is the effect of insertions?
- every three bases in a DNA base sequence codes for a particular amino acid.
-an insertion changes the way the groups of three bases are ‘read’ which can change the amino acids that they code for.
How can insertions change more than one amino acid?
- Insertions can change more than one amino acid as they have a knock on effect on the bases further on the sequence.
What are deletions and what is the effect of deletions?
- deletions are where a random base is deleted from the DNA base sequence.
- they change the way that the base sequence is ‘read’ and have knock on effects further down the sequence.
What are substitutions?
Substitution mutations are when a random base in the DNA base sequence is changed to a different base.
What is sexual reproduction?
where genetic information from 2 organisms (a father and a mother) is combined to produce offspring which are genetically different to either parent.
What happens in sexual reproduction?
The mother and father produce gametes by meiosis (an egg and sperm cells in animals).
The egg and the sperm cell then fuse together fertilisation) to form a cell with the full number of chromosomes.
How chromosomes are in each gamete in humans?
23 (instead of having 2 of each chromosomes, a gamete has just one of each)
What does sexual reproduction involve?
The fusion of male and female games. Because there are 2 parents, the offspring contain a mixture of their parent’s genes.
What produces variation in sexual reproduction?
this mixture of genetic information
What are the gametes of sexual reproduction of flowering plants?
egg cells but their version of sperm is known as pollen.
What happens in asexual reproduction?
In asexual reproduction there’s 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.
By what process does asexual reproduction occur?
mitosis
Give examples of organisms that reproduce asexually.
bacteria, some plants and some animals.
How are gametes which only have half of the original number of chromosomes made?
by cells dividing by meiosis. This process involves 2 cell divisions. In humans, it only happens in the reproductive organs.
What is a haploid cell?
A cell that only has half the normal amount of genetic material
When does a diploid cell form?
When two haploid cells join,
What are the 4 steps of meiosis?
1) Before the cell starts to divide, it duplicates its genetic information, forming 2 armed chromosomes- one arm of each chromosomes is an exact copy of the other arm. After replication the chromosomes arrange 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 have one copy of each chromosome. Some of the father’s chromosomes and some of the mother’s chromosomes go into each new cell.
4) In the second division, the chromosomes line up again in the centre of the cell. The arms of the chromosomes are pulled apart.
Are the games produced by meiosis genetical identical or different and why?
You get four gametes: each with only a single set of chromosomes in it. Each of the games 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.
What happens after 2 gametes have fused during fertilisation?
- the resulting cell divides by mitosis to make a copy itself.
-mitosis repeats many times to produce lots of new cells in an embryo. - as the embryo develops these cells then start to differentiate into the different types of specialised cell that make up a whole organism.
What are the advantages of sexual reproduction?
1) Offspring from sexual reproduction has a mixture of 2 sets of chromosomes. The organism inherits genes from both parents, which PRODUCES VARIATION in the offspring.
2) Variation increases the chance of a species surviving a change in the environment. They have a survival advantage.
3) Because individuals with characteristics that make them better adapted to the environment have a better chance of survival, they are more likely to breed successfully and pass the genes for the characteristics on. This is known as natural selection.
4) We use selective breeding to SPEED UP natural selection.
aqa spec:
produces variation in the offspring
if the environment changes variation gives a survival advantage by natural selection
natural selection can be speeded up by humans in selective breeding to increase food production.
What does speeding up natural selection allow us to produce?
This allows us to produce animals with desirable characteristics. Selective breeding is where individuals with a desirable characteristics are bred to produce offspring that have the desirable characteristics too. This means that we can increase food production.
What are the advantaged of asexual reproduction?
-only one parent needed
-more time and energy efficient as do not need to find a mate
-faster than sexual reproduction
-many identical offspring can be produced when conditions are favourable.
What are the 3 examples of organisms that can reproduce both sexually and asexually?
- malaria
-many fungal species
-species of plants
How can malaria reproduce both sexually and asexually?
Malaria is caused by a parasite that’s spread by mosquitos. Malarial parasites reproduce asexually in the human host, but sexually in the mosquito.
How can species of fungus reproduce both sexually and asexually?
- Many fungi reproduce asexually by spores but also reproduce sexually to give variation.
- Asexually produces spores produced 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 in survive the change.
How can species of plants reproduce both sexually and asexually?
Many plants produce seeds sexually, but also reproduce asexually by runners such as strawberry plants, or bulb division such as daffodils.
The runners of strawberry plants are stems that grow horizontally on the surface of the soil away from the plant. At various points along the runner a new strawberry plant forms that is identical to the original plant.
New bulbs form from the main bulb and divide off. Each bulb can grow into a new identical plant.
What do the different pairs of chromosomes in the total 23 in the human body control?
Ordinary human body cells contain 23 pairs of chromosomes.
22 pairs control characteristics only, but one of the pairs (the 23rd pair) carries the genes that determine sex.
What are the 23rd pair of chromosomes called and what does the represent?
XY or XX
- males have an X and a Y chromosome: XY. The Y chromosomes causes male characteristics.
- Females have 2 X chromosomes: XX. The XX chromosomes allows female characteristics to develop.
What happens when making sperm?
The X and Y chromosomes are drawn apart in the first division in meiosis. There’s 50% chance each sperm cell gets and X chromosomes and a 50% chance it gets a Y chromosome.
What happens when making eggs?
A similar things happens when making eggs. But the original cell has 2 chromosomes, so all the eggs have one X chromosomes.
What are genetic diagrams?
models that are used to show all the possible genetic outcomes when you cross together different genes or chromosomes.
What characteristics are controlled by a single gene?
Some characteristics are controlled by a single gene, such as: fur colour in mice; and red-green colour blindness in humans.
What are alleles?
Each gene may have different forms /versions called alleles.
What is a homozygous trait?
If an organism has 2 alleles for a particular gene that are all the same then it’s homozygous for that trait.
What happens if the 2 alleles are different?
Only one can determine what characteristics is present. The allele for the characteristics that’s shown is called the dominical allele. The other one is recessive.
What is a heterozygous trait?
If its two alleles for a particular gene are different then it’s heterozygous.
How are dominant and recessive alleles shown?
- dominant are shown using capital letters
-recessive are shown using small laters
What must happen for an organism to display the recessive characteristic?
- both its alleles must be recessive
What must happen for an organism to display the dominant characteristic?
The organism can be either CC or Cc because the dominant allele overuses the recessive one if the plant/animal/organism is heterozygous.
What is genotype?
Your genotype is the combination of alleles you have.
What is phenotype?
Your alleles work at a molecular level to determine what characteristics you have.
What are most phenotype features a result of?
most phenotype features are the result of multiple genes rather than single gene inheritance.
What are inherited diseases caused by?
Some disorders are inherited. These disorders are caused by the inheritance of certain alleles.
What are 2 examples of inherited diseases?
- Polydactyly (having extra fingers or toes) is caused by a dominant allele.
- Cystic fibrosis (a disorder of cell membranes) is caused by a recessive allele.
What does cystic fibrosis cause?
It results in the body producing a lot of sticky mucus in the air passages and in the pancreas.
How is cystic fibrosis caused? (4)
1) The allele which causes cystic fibrosis is a recessive allele “f” carried by about 1 person in 25.
2) Because it’s recessive people with only one copy of the allele won’t have the disorder; they’re known as carriers.
3) For a child to have the disorder, both parents must be either carriers or have the disorder themselves.
4) A child has a 1 in 4 chance of having the disorder if both parents are carriers.
How is polydactyly caused?
1) The disorder is caused by a dominant allele “D” and so can be inherited if just one parent carries the defective allele.
2) The parent that has the defective allele will have the condition too since the allele is dominant.
3) There is a 50% chance of a child having the disorder if one parent has one D allele.
What happens during in vitro fertilisation (IVF)?
embryos are fertilised in a laboratory and then implanted into the mother’s womb.
How can embryos be scanned?
1) Before being implanted, it’s possible to remove a cell from each embryo and analyse its genes.
2) Many genetic disorders can be detected in this way, such as cystic fibrosis.
3) It’s also possible to get DNA from an embryo in the womb and test that for disorders.
Why can embryo screening be seen as controversial?
- For embryos produced by IVF: after screening the embryos with “bad” alleles would be destroyed.
- For embryos produced in the womb: screening could lead to the decision to terminate the pregnancy.
What are 3 arguments against embryonic screening?
1) It implies that people with genetic problems are ‘undesirable’- this could increase prejudice.
2) There may come a point where everyone wants to screen their embryo so they can pick the most ‘desirable’ one.
3) Screening is expensive.
What are 3 arguments for embryonic screening?
1) It will help to stop people suffering.
2) Treating disorders costs the government (and the taxpayers) a lot of money.
3) There are laws to stop it going too far. At the moment parent cannot even select the sex of the baby (even if it’s for health problems).
What did Gregor Mendel note during his genetic experiment with pea plants?
He noted how characteristics in plants were passed on from one generation to the next. There results of his research were published in 1866 and eventually become the foundation of modern genetics.
What had Mendel shown?
Mendel had shown that the height characteristics in pea plants was determined by separately inherited “hereditary units” passed on from each parent. The ratios of tall and dwarf plants in the offspring showed that the unit for tall plants, T, was dominant over the unit for the dwarf plants, t.
What were the 3 important conclusions Mendel reached?
1) Characteristics in plants are determined by “hereditary units”.
2) Hereditary units are passed on to offspring unchanged from both parents, one unit from each parent.
3) Hereditary units can be dominant and recessive: if an individual has both the dominant and the recessive unit for a characteristic, the dominant characteristic will be expressed.
Why was Mendel’s work’s significance not realised until after his death?
They didn’t have the background knowledge to properly understand his findings- they had no idea about genes, DNA and chromosomes.
How was Mendel’s work as starting point for the different observations of scientists about the understanding of genes?
- In the late 1800s, scientists became familiar with chromosomes. They were able to observe how they behaved during cell division.
-In the early 20th Century it was observed that chromosomes and Mendel’s ‘units’ behaved in similar ways. This led to the idea that the ‘units’, now called genes, were located on chromosomes. - In the mid-20th Century the structure of DNA was determined and the mechanism of gene function worked out.
-In 1953, the structure of DNA was determined. This allowed scientists to go on and find out exactly how genes worked.
What is variation?
Differences in the characteristics of individuals in a population is called variation.
What are the 2 types of variation?
genetic variation end environmental variation.
What is variation due to?
- the genes they have inherited (genetic causes)
- the conditions in which they have developed (environmental causes)
- a combination of genes and the environment.
Why do animals and plants have characteristics that are in some ways similar to their ‘parents.’
An organism’s characteristics are determined by the genes inherited from their parents. (genes are the codes inside your cells that control how you’re made)
How is genetic variation caused?
- these genes are passed on in sex cells (gametes) from which the offspring develop.
- most animals get some genes from the mother and some from the father.
- this combining of genes from 2 parents causes genetic variation; no two of the species are genetically identical.
What are some characteristics determined only by genes in animals?
-eye colour
-blood group
-inherited disorders (haemophilia or cystic fibrosis)
What is environmental variation?
The environment, including the conditions that organisms live and grow in, also causes difference between members of the same species- this is called environmental variation.
What are some examples of characteristics influenced by the environment?
- a plant grown in plenty of sunlight would be luscious and green.
- a plant grown in darkness would grow tall and spindly and have yellow leaves.
-getting a suntan.
What are most characteristics due to?
Most characteristics (e.g. body weight, height, skin colour, condition of teeth, academic/athletic prowess etc) are determined by a mixture of genetic and environmental factors.
The maximum height that an animal or plant could grow is determined to its genes but whether it actually grows that tall depends on its environment.
What do all variants arise from and what does this mean?
all variants arise from mutations
- most mutations have no affect on the protein the gene codes for so have no effect on the phenotype
- some influence phenotype so alter characteristics very slightly.
- very few determine phenotype. (New phenotype being seen in a species).
How can a new phenotype become common throughout the species quickly?
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.
What is evolution?
a change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species.
What is the theory of evolution?
The theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago.
What is Charles Darwin known for?
Charles Darwin, as a result of observations on a round the world expedition, backed by years of experimentation and discussion and linked to developing knowledge of geology and fossils, proposed the theory of evolution by natural selection.
What was Charles Darwin’s idea?
- he knew that organism in a species show wide variation in their characteristics (phenotypic variation). He also knew that organisms have to compete for limited resources in ecosystem.
-Darwin concluded that organisms with the most suitable characteristics for the environment. This called the “SURVIVAL OF THE FITTEST.”
What happens in the idea of survival of the fittest?
- the successful organisms that Survive and more likely to REPRODUCE and pass on the genes for the characteristics that made them successful to their offspring.
- the organisms that are less well adapted would be less likely to survive and reproduce so they are less likely to pass on the genes.
What happens to the beneficial characteristics over time (survival of the fittest)?
become more common in the population and the species changes- it evolves.
Why was Darwin’s theory not perfect when he made it and published his ideas in On the Origin of Species (1859)?
the relevant scientific knowledge wasn’t available at the time, he couldn’t give a good explanation for why new characteristics appeared or exactly how individual organisms passed on beneficial adaptations to their offspring.
How have new discoveries helped to develop the theory?
We know that phenotype is controlled by genes. New phenotypic variations arise because of genetic variants produced by mutations. Beneficial variations are passed on to future generations in the genes that parents contribute to their offspring.
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- this is called speciation.
How does speciation occur?
Speciation happens when populations of the same species change enough the become reproductively isolated- this means that they can’t interbreed to produce fertile offspring.
What are the 5 reasons why a species becomes extinct?
1) The environment changes too quickly (e.g. destruction of a habitat).
2) A new predator kills them all (e.g. humans hunting them).
3) A new disease kills them all.
4) They can’t compete with another (new) species for food.
5) A catastrophic event happens that kills them all (e.g. a volcanic eruption or a collision with an asteroid).
When does extinction occur?
Extinctions occur when there are no remaining individuals of a species still alive.
What were the 3 reasons why the theory of evolution by natural selection was only gradually accepted because?
- 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
- the mechanism of inheritance and variation was not known until 50 years after the theory was published.
What was Lamarck’s theory?
Lamarck argued that changes that an organisms acquires during its lifetime will be passed on to its offspring,- e.g. he thought that if a characteristic was used a lot by an organism then it would become more developed during its lifetime and the organism’s offspring would inherit the acquired characteristic.
How can a hypothesis be checked to see if it is right or wrong?
by finding evidence that supports or disproves it.
What eventually happened to Lamarck’s theory and why?
rejected as experiments didn’t support his hypothesis.
Example; if you dye a hamster’s fur bright pink, its offspring will still be born with the normal fur colour because the new characteristic won’t have been passed on.
How did the discovery of genetics support Darwin’s idea?
- It provided an explanation of how organisms born with beneficial characteristics can pass them on.
- Other evidence was also found by looking at fossils of different ages; this allows you to see how changes in organism developed over time. The relatively recent discovery of how bacteria are able to evolve to become resistant to antibiotics also further supports evolution by natural selection.
(there is so much evidence for Darwin’s idea that it’s now an accepted hypothesis).
What is selective breeding?
Selective breeding (artificial selection) is the process by which humans breed plants and animals for particular genetic characteristics. Humans have been doing this for thousands of years since they first bred food crops from wild plants and domesticated animals.
What are 3 examples of selective breeding?
- animals that produce more meat or milk.
- crops with disease resistance.
- dogs with a good, gentle temperament.
- decorative plants with big or unusual flowers.
What is the basic process involved in selective breeding?
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 of 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 characteristic.
What is the main problem of selective breeding?
- it reduces the gene pool; the number of different alleles in a population.
Why does the gene pool reduce in selective breeding?
as the farmer keeps breeding from the “best” animals or plants; which are all closely related- this is known as inbreeding.
Why does inbreeding cause health problems?
there’s more chance of the organism inheriting harmful genetic defects when the gene pool is limited.
(some dog breeds are particularly susceptible to certain defects due to inbreeding.
Why is a new disease appearing paired with inbreeding a serious problem?
there’s not much variation in the population. All the stock are closely related to each other so if one of them is going to be killed by a new disease, the others are also likely to succumb to it.
What is genetic engineering?
a process which involves modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic.
What happens in genetic engineering?
In genetic engineering, genes from the chromosomes of humans and other organisms can be ‘cut out’ and transferred to cells of other organisms.
What is the process of genetic engineering?
- enzymes are used to isolate the required gene; this gene is inserted into a vector, usually a bacterial plasmid or a virus depending on the type of organism that the gene is being transferred to.
- the vector is used to insert the gene into the required cells.
- 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.
Give examples of genetic engineering?
- Plant crops have been genetically engineered to be resistant to diseases or to produce bigger better fruits. (GM crops)
- Bacterial cells have been genetically engineered to produce useful substances such as human insulin to treat diabetes.
- Sheep have been genetically engineered to produce substances like drugs in their milk that can be used to treat human diseases.
- Scientists are researching genetic modification treatment for inherited diseases caused by faulty genes e.g. by gene therapy.
What is gene therapy?
by inserting working genes into people with a disease caused by a faulty gene.
What are GM crops?
Crops that have had their genes modified in this way are called genetically modified (GM) crops. GM crops include ones that are resistant to insect attack or to herbicides. GM crops generally show increased yields.
What are the cons for GM crops?
- some say it will affect the number of wild flowers and so the population of insects that live in and around the crops reducing farmland biodiversity.
-Some people feel the effects of eating GM crops on human health have not been fully explored.
-A big concern is that transplanted genes may get out into the natural environment. (herbicide resistance gene may be picked up by weeds)
What are the pros for GM crops?
- the characteristics chosen for GM crops can increase the yield, making more food.
-People living in developing nations often lack nutrients and this can provide this missing nutrient.
-GM crops are already being grown in some places often without any problems.
Give an example of a GM crop.
‘Golden rice’ is a GM rice crop that contains beta carotenes, lack of this substance causes blindness.
What are the 2 ways plants can be cloned?
tissue culture and cuttings.
What is tissue culture?
This is where a few plant cells are put in a growth medium with hormones and they grow into new plants- clones of the parent plant. These plants can be made very quickly, in very little space and be grown all year. Tissue culture is used to preserve rare plants that are hard to be reproduce naturally or commercially in nurseries.
How are cuttings used for cloning?
1) Gardeners can take cuttings from good parent plants and then plant them to produce genetically identical copies/clones of the parent plant.
2) These plants can be produced quickly and cheaply. This is an older, simpler method than tissue culture.
How can animal clones be made using embryo transplants?
splitting apart cells from a developing animal embryo before they become specialised, then transplanting the identical embryos into host mothers.
What is the process of embryo transplants that farmers use to produce cloned offspring from their best bull and cow?
1) Sperm cells are taken from a prize bull and egg cells are taken from a prize cow. The sperm are then used to artificially fertilise an egg cell. The embryo that develops is then split many times (to form clones) before any cells become specialised.
2) These cloned embryos cam then be implanted into lots of other cows where they grow into baby calves (which will all be genetically identical to each other).
3) Hundreds of “ideal” offspring can be produced every year from the best bull and cow.
How is adult cloning another way to make a clone?
1) The nucleus is removed from an unfertilised egg cell.
2) The nucleus from an adult body cell, such as a skin cell, is inserted into the egg cell.
3) An electric shock stimulates the egg cell to divide to form an embryo.
4) These embryo cells contain the same genetic information as the adult skin cell.
5) When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue its development.
What are the concerns surrounding cloning?
- gives a “reduced gene pool”
-it’s possible that cloned animals might not be as healthy as normal ones e.g. dolly the sheep had arthritis. - some people work that humans might be cloned: if it was allowed, any success may follow many unsuccessful attempts.
What are the advantages of cloning?
- the study of animal clones could lead to greater understanding of the development of the embryo and of ageing and age related disorders.
- cloning could be used to help preserve endangered species.
What are fossils?
Fossils are the ‘remains’ of organisms from millions of years ago, which are found in rocks
What do fossils tell us/ provide evidence for?
We can learn from fossils how much or how little different organisms have changed as life developed on Earth.
What are the 3 ways that fossils form in rocks?
1) From gradual replacement by minerals.
2) from casts and impressions.
3) from preservation in places where no decay happens.
How are fossils formed from gradual replacement by minerals?
1) Things like teeth, shells, bones etc., which don’t decay easily can last a long time when buried.
2) They’re 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 rick, but the fossil stays distinct inside the rock and eventually someone digs it up.
How are fossils formed from casts and impressions?
1) Sometimes fossils are formed when an organism is buried in a soft material like clay. The clay later hardens around it and the organism decays leaving a cast of itself. An animal’s burrow or a plant’s roots can be preserved as casts.
2) Things like footprints can also be pressed into these materials when soft, leaving an impression when it hardens.
How are fossils from preservation in places where no decay happens?
1) In amber (a clear yellow ‘stone’ made from fossilised resin) and tar pits there’s no oxygen or moisture so decay microbes can’t survive.
2) In glaciers it’s cold for the decay microbes to work.
3) Peat bogs are too acidic for decay microbes.
Why cannot scientists be certain about how life began on Earth?
Many early forms of life were soft-bodied, which means that they have left few traces behind.
What traces (fossils that did form millions of years ago) there were have been mainly destroyed by geological activity. (e.g. the movement of tectonic plates may have crushed fossils already formed in the rock).
What is a species?
a group of similar organisms that can reproduce to give fertile offspring.
What is speciation?
the development of a new species.
When does speciation occur?
When population of the same species become so different that they can no longer successfully interbreed to produce fertile offspring.
What are the two parts to speciation?
1) SEPARATION (physical/ geographical barrier): this means the two groups cannot interbreed. Conditions on either side are different.
2) NATURAL SELECTION now occurs on each side:
-mutations cause variations on each side
-this leads to competition to get resources on each side
-those better adapted will survive and reproduce on each side.
- they will pass on genes to the next generation. (the alleys that control the beneficial characteristics are more likely to be passed on to the next generation).
How does speciation result in the development of a new species?
Over time each populations will change genetically and if brought back together again they cannot breed to produce FERTILE and VIABLE offspring.
Who was Alfred Russel Wallace?
a scientist working at the same time as Charles Darwin. He was one of the early scientists working the idea of speciation. His observations greatly contributed to how we understand speciation today. Our current understanding developed as more evidence became available over time.
What idea did Wallace independently come up with?
Alfred Russel Wallace independently proposed the theory of evolution by natural selection. He published joint writings with Darwin in 1858 which prompted Darwin to publish On the Origin of Species (1859) the following year.
What did Wallace observe as he travelled the world and what is he best known for?
Wallace worked worldwide gathering evidence for evolutionary theory. He is best known for his work on warning colouration in animals (to deter prey from eating them) and his theory of speciation.
How can bacteria become resistant to antibiotics.
Bacteria can evolve rapidly because they reproduce at a fast rate.
Mutations of bacterial pathogens produce new strains. Some strains might be resistant to antibiotics, and so are not killed. They survive and reproduce, so the population of the resistant strain rises.
How is being able to resist antibiotics is a big advantage to the bacteria?
It’s better able to survive even in a host who is being treated to get rid of the infection and so it lives for longer and reproduces many more times. This increases the population size of the antibiotic resistant strain.
Why are antibiotic resistant strains a problem for people who become infected?
The resistant strain will then spread because people are not immune to it and there is no effective treatment. This means that the infection spreads easily between people.
What is an example of a bacterial ‘superbug’ that is resistant to most known antibiotics?
MRSA is resistant to antibiotics.
It often affects people in hospitals and can be fatal if it enters their bloodstream.
What can be done by doctors/patients to reduce the rate of development of antibiotic resistant strains?
- doctors should not prescribe antibiotics inappropriately, such as treating non-serious or viral infections.
- patients should complete their course of antibiotics so all bacteria are killed and none survive to mutate and form resistant strains.
What can be done be farmers to reduce the rate of development of antibiotic resistant strains?
the agricultural use of antibiotics should be restricted:
- in farming antibiotics can be given to animals to prevent them becoming ill and make them grow faster.
- this can lead to the development of antibiotics resistant bacteria in the animals which can then spread to to humans (during meat preparation and consumption).
Why is it difficult for antibiotics that work against bacteria to be produced?
The rate of development of new antibiotics is costly and slow. It is unlikely to keep up with the emergence of new resistant strains more antibiotic resistant strains develop and spread.
How have living things traditionally been classified and why?
Traditionally living things have been classified into groups depending on their structure and characteristics in a system developed by Carl Linnaeus.
What system is living organisms grouped in and what is the order?
Linnaeus classified living things into the Linnaean system:
kingdom, phylum, class, order, family, genus and species.
(kings play chess on fancy green stools)
Why were new models of classification were proposed?
As evidence of internal structures became more developed due to improvements in microscopes, and the understanding of biochemical processes progressed.
What did Carl Woese propose in 1990 and why?
- three domain system.
- using evidence gathered from new chemical analysis techniques such as RNA sequence analysis, he found that in some cases species thought to be closely related in traditional classification systems are in fact not as closely related as first thought.
What does the three domain system consist of?
1) Archaea (primitive bacteria usually living in extreme environments such as hot springs + salt lakes).
2) Bacteria (true bacteria like E coli and staphylococcus). Although they look similar to archaea there is a lot of biochemical differences between them.
3) Eukaryota (a broad range of organisms including protists, fungi, plants and animals).
(they are then subdivided into smaller groups, kingdom, phylum, class, order, family, genus and species.)
What are organisms named by?
Organisms are named by the binomial system of genus and species.
1st part refers to the genus (provides information on the organism’s ancestry) , the 2nd part refers to the species.
What is the binomial name for humans?
Homosapiens
homo= human’s genus
sapiens=human’s species
What do evolutionary trees show?
Evolutionary trees are a method used by scientists to show how they believe organisms are related.
How do evolutionary trees show a close evolutionary relationship?
The more common ancestors they have and the more recent the common ancestor, the more closely they are related- and so share more likely they are to share more characteristics.
What do scientists analyse for evolutionary trees?
they use current classification data for living organisms and fossil data for extinct organisms.
