Flashcards in B6:Inheritance, Variation And Evolution Deck (168):
What is DNA?
A chemical that all of the genetic material in a cell is made up from.
What does DNA contain?
Coded information - All the instructions to put an organism together and make it work.
What is in your DNA determines...
What inherted characteristics you have.
DNA is found…
In the nucleus of animal and plant cells in your chromosomes.
Chromosomes normally come in...
DNA is a...
It is made of...
Polymer - made up of two strands coiled together in the shape of a double helix.
What is a gene?
A small section of DNA found on a chromosome.
Each gene codes for...
A particular sequence of amino acids which are put together to make a specific protein.
How many amino acids are used?
20 but they make up thousands of different proteins.
What do genes do?
Simply tell cells in what order to put the amino acids together.
DNA also determines...
What proteins the cell produces - which determines the type of cell it is.
The entire set of genetic material in an organism.
How is the human genome useful for medicine? (2)
- scientists can see genes that are linked to different diseases.
- this could help us to understand them and get effective treatments for them.
Scientists can look at genomes to...
Trace the migration of certain populations of people around the world.
Explain how the human genome has changed: (2)
By investigating these differences...
- All humans descended from a common ancestor in Africa.
- The human genome is identical but we have developed tiny differences as we have migrated from Africa.
- By investigating these differences, scientists can work out when new populations split up and what route they took.
What is Sexual Reproduction?
Where genetic information from two organisms is combined to produce genetically different offspring.
What do the mother and father produce during Sexual Reproduction? By what?
Gametes - egg and sperm cells. By Meiosis.
In humans, each gamete contains...
23 chromosomes - half the number in a normal cell.
What happens to the egg and sperm during Sexual Reproduction?
They fuse together (fertilisation) to form a cell with the full number of chromosomes.
So, Sexual Reproduction involves...
The fusion of male and female gametes.
Why does the offspring inherit features from both parents in Sexual Reproduction?
Because it has received a mixture of chromosomes from its Mum and Dad.
What produces variation in the offspring?
The mixture of genetic information.
What else reproduces sexually?
Flowering plants - their version of sperm is pollen.
In Asexual Reproduction: (3)
- Only one parent.
- No fusion of games.
- No mixing of chromosomes.
What are the offspring genetically like in Asexual Reproduction?
Clones - the exact same genetic information as the parent cell.
What cell division does Asexual Reproduction happen by?
Mitosis - an ordinary cell makes a new cell by dividing in two.
Give 3 examples of things that reproduce Asexually:
- some plants.
- some animals.
Why do gametes only have one copy of each chromosome?
So that when gamete fusion happens, you get the right amount of chromosomes again.
2 cell divisions.
Give the first 2 steps of Meiosis:
1) cell = duplicates genetic info, forms 2 armed chromosomes (exact copies rearranged in pairs)
2) 1st division = chromosome pairs line up in the centre of the cell.
Give the last 2 steps of Meiosis:
3) pairs are pulled apart so each new cell only has one copy of each chromosome (some of the fathers and some of the mothers chromosomes go in each cell)
4) 2nd Division: chromosomes line up again in the centre and the arms of the chromosomes are pulled apart.
What is the result of Meiosis?
What are the gametes like?
You get 4 gametes each with only a single set of Chromosomes.
Each of the gametes are genetically different because the chromosomes gets shuffled up during Meiosis and each gamete only gets half of them at random.
What happens after two gametes have fused during fertilisation?
The resulting 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, what happens to the cells?
They start to differentiate into different types of specialised cells that make up a whole organism.
What is so special about the 23rd pair of chromosomes in our cells?
They determine our sex.
What is a males genotype?
What is a females genotype?
What is the probability a sperm cell gets an X chromosomes and a Y?
What are Genetic Diagrams?
Models that are used to show all the possible genetic outcomes when you cross together different genes or chromosomes.
What genes you inherit control...
What characteristics you develop.
Different genes control...
Different characteristics e.g. hair colour.
SOME characteristics are controlled by a single gene. Give 2 examples:
- mouse fur colour.
- red-green colour blindness in humans.
Most characteristics are controlled by...
Several genes interacting.
What does it mean if an organism has two of the same alleles for a particular gene?
They are homozygous for that trait.
What does it mean if an organism has two different alleles for a particular gene?
They are heterozygous for that trait.
What are alleles?
Different versions of genes.
If two alleles are different, which determines what characteristics is present?
The dominant allele. (Represented by a capital letter)
What is a recessive allele?
For an organism to display this, both alleles must be recessive.
What is a dominant allele?
Only one dominant allele is needed to overrule the recessive one.
Your genotype is..
The combination of alleles you have.
Your phenotype is...
The characteristics you have.
What do genetic diagrams show?
The possible alleles of offspring.
What is Cystic Fibrosis?
A genetic disorder of the cell membranes.
What does Cystic Fibrosis result in?
The body producing a lot of thick sticky mucus in the air passages and in the pancreas.
The allele which causes Cystic Fibrosis is...
A recessive and is carried by about 1 in 25 people.
What if you only had one copy of the recessive allele that causes Cystic Fibrosis?
You are just a carrier.
For a child to have the disorder of Cystic Fibrosis...
Both parents must be carriers or have the disorder themselves.
What is Polydactyly?
A genetic disorder where a baby’s born with extra fingers or toes.
Polydactyly is caused by... (what allele?)
A dominant allele, so it can be inherited if just one person carries the defective allele.
Before an embryo is important planted in the womb for IVF, what can you do?
It’s possible to remove a cell from each embryo and analyse its genes.
What does Embryo Screening mean you can do?
Detect genetic disorders e.g. Cystic Fibrosis.
How else can you test an embryo for disorders?
Get the DNA and test it.
Embryo Screening is quite...
For embryos produced by IVF, what would happen if a genetic disorder was found?
Embryos with ‘bad’ alleles would be destroyed.
For embryos in the womb, what would happen if a genetic disorder was found?
To terminate the pregnancy.
Give 3 reasons for being AGAINST Embryonic Screening:
- Implies people with genetic problems are undesirable.
- Screening is expensive.
- People may want to screen so they can pick the most desirable embryos.
Give 3 reasons for being FOR Embryonic Screening:
- It will help to stop people suffering.
- Treating disorders costs the Government a lot of money.
- There are laws to stop things going too far e.g. parents cannot select the sex of their baby.
What is Variation?
Differences within a species.
Most variation in phenotype is determined by a mix of... (2)
- your genotype. (genetics)
- environmental conditions.
An organism’s genotype affects its...
Occasionally, what can happen to a gene?
It can mutate.
What is a mutation?
A mutation is a rare, random change in an organism’s DNA that can be inherited.
What do mutations mean?
That the gene is altered - which produces a genetic variant. (a different form of the gene)
What happens as the gene codes for a sequence of amino acids that make up a protein?
Gene mutations sometimes lead to changes in the protein that it codes for.
What effect do most genetic variants have on the protein the gene codes for?
Very little or no effect. Some will change it to such a small extent that its function is unaffected.
Most mutations have no effect on an organism’s...
Some variations have...
A small influence on the organism’s phenotype - they alter the individual’s characteristics.
Give an example of a small influence made on the organism’s influence:
E.G. Eye colour is controlled by more than one gene. A mutation in one of the genes may change the eye colour a bit but the difference may not be huge.
Variants can have a dramatic effect that they determine phenotype.
Give an example of a variant having such a dramatic effect that it determines phenotype:
Cystic Fibrosis - gene codes for a protein that controls the movement of salt/water in and out cells.
Protein produced by mutated gene = doesn’t work properly.
Leads to excess mucus production in the lungs and digestive system - difficult to breathe and to digest food.
What is the Theory of Evolution?
All of today’s species have evolved from simple life forms that first started to develop over 3 billion years ago.
Who came up with ‘Evolution by Natural Selection’?
Darwin knew that...
Organisms in a species show wide variation in their characteristics and that they have to compete for limited resources.
Darwin concluded that...
Organisms with the most suitable characteristics for the environment are more successful competitors and end up surviving.
The successful organism that survive are...
More likely to reproduce and pass on the genes for the characteristics that made them successful to their offspring.
What happens to the organism that are less well adapted?
They are less likely to survive and reproduce.
Beneficial characteristics become more common in the population.
Why was Darwin’s theory not perfect? (2)
- there wasn’t enough scientific knowledge to explain why new characteristics developed.
- or how organisms passed them on their offspring.
How did the discovery of genetics support Darwin’s idea?
It provided an explanation of how organisms born with certain characteristics can pass them on (via their genes) and that it is genetic variants that give rise to the phenotypes better suited.
What other evidence supported Darwin’s theory?
- fossil record - showed how organisms developed slowly over time.
- how bacteria can evolve and become resistant supports evolution.
Over a long period of time, what can happen to a species?
Their phenotype can change so much because of natural selection that a completely new species is formed.
What is Speciation?
The development of new species.
Speciation happens when...
Populations of the same species change enough to become reproductively isolated.
What does it mean if a species is reproductively isolated?
They can’t interbreed to produce fertile offspring.
How can species be extinct? (5)
- environment changes e.g. destruction of habitat.
- new predator kills them.
- new disease kills them.
- can’t compete with other species for food.
- a catastrophic event kills them all.
What is Selective Breeding?
When humans artificially select the plants/animals that are going to breed so that the genes for a particular characteristics remains in the population.
Organisms are selectively bred to...
Develop features that are useful or attractive.
Give an example of things that can be selectively bred: (4)
- Animals that produce more meat or milk.
- Crops with disease resistance.
- Dogs with good gentle temperament.
- Decorative plants with big or unusual flowers.
Give the 4 steps to selective breeding:
1) Select, from your stock, the ones which have the characteristics you’re after.
2) Breed them with each-other.
3) Select the best offspring and breed them together.
4) Continue this over several generations and the desirable trait gets stronger.
What is the result of Selective Breeding?
Eventually, all the offspring will have the characteristic.
What can Selective Breeding be used for in farming?
To improve yields e.g. a farmer could breed cows/bulls with the best characteristics for producing meat.
Selective breeding has been going on for...
Thousands of years.
Selective Breeding is how we ended up with... (2)
- edible crops from wild plants.
- domesticated animals like cows and dogs.
The main problem with selective breeding is that...
It reduces the gene pool - the number of different alleles in a population.
Why does Selective Breeding reduce the gene pool?
Because the farmer keeps breeding from the “best” animals/plants which are all closely related - this is known as “inbreeding.”
Inbreeding can cause...
Health problems because there’s more chance of the organisms inheriting harmful genetic defects when the gene pool is limited.
Why is it a problem if a new disease appears in a population of selectively bred things?
There’s not much variation in the population so if one of them is going to be killed by the disease, the others will too.
What is Genetic Engineering?
It transfers a gene responsible for a desirable characteristic from one organisms genotype into another organism so that it also has the desired characteristics.
Give the 2 steps to Genetic Engineering:
1) A useful gene is isolated from one organism’s genome using enzymes and is inserted into a vector.
2) When the vector is introduced to the target organism, the useful gene is inserted into its cells.
The vector is usually...
A virus or a bacterial plasmid depending on the type of organism that the gene is being transferred to.
How have Bacteria been genetically modified?
To produce human insulin that can be used to treat diabetes.
How have GM Crops been modified?
To improve the size and quality of their fruit or make them resistant to disease, insects and herbicides.
How have Sheep been genetically engineered?
To produce substances like drugs in their milk that can be used to treat human diseases.
Scientists are researching genetic modification treatments for...
Inherited diseases caused by faulty genes - this is called gene therapy.
In some cases, when is the transfer of gene in Genetic Engineering carried out?
When the organism receiving it is at an early stage of development - so the organism develops with he characteristic.
Genetic Engineering has the potential for...
Solving many of our problems but not everyone thing it’s a great idea.
Disadvantages of GM Crops: (2)
- GM Crops will affect the number of wild flowers that live around the crops - reducing farmland biodiversity.
- Transplanted genes may get out into the natural environment.
Explain why people think GM Crops aren’t safe: (Disadvantage)
They’re concerned we might not fully understand the effects of eating them on human health e.g. developing allergies.
Advantages of GM Crops: (2)
- The characteristics chosen for them will increase the yield.
- GM Crops are already being grown in some places without problems.
Explain how GM Crops could help people with a lack of nutrients: (Advantage)
People may lack nutrients - GM Crops could be engineered to contain the nutrient that’s missing.
Give a disadvantage of Genetic Engineering:
Changing an organism’s genes might accidentally create unplanned problems which will get passed on to future generations.
What are Fossils?
The remains of organisms from many thousands of years ago which are found in rocks.
Fossils provide evidence that...
Organisms lived ages ago and they can tell use how much or how little organisms have changed over time.
Name the 3 ways Fossils can be made:
- From gradual replacement by minerals.
- From casts and impressions.
Give the 3 points about Fossils happening from “Gradual Replacement by Minerals”:
1) Things like teeth, shells, bones etc won’t decay easily and can last a long time.
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 rock, but the fossil stays distinct inside the rock and eventually someone digs it up.
Give the 2 points about Fossils forming from “Casts and Impressions”:
1) Sometimes they form when something is buried in a soft material like clay. The clay hardens as the organism decays leaving a cast.
2) Things like footprints can also be pressed into these materials when soft, leaving an impression when it hardens.
Give 2 examples of things that can be preserved as casts:
- An animal’s burrow.
- A plant’s roots.
Give the 3 points about Mummification:
1) In amber and tar pits, there’s no oxygen or moisture so decay microbes can’t survive.
2) In glaciers, it’s too cold for them to work.
3) Peat bogs are too acidic for decay microbes.
Give 2 hypotheses on how life first came into being:
1) Maybe then came in a primordial swamp.
2) Maybe simple organic molecules were brought on comets - these could have became complex then eventually very simple life forms.
Why can’t hypotheses about how life began be supported?
Because there’s a lack of good, valid evidence.
Why is there a lack of good, valid evidence for how life began? (2)
- Many early forms of life were soft bodied and soft tissue decays away completely.
- Fossils that did form millions of years ago may have been destroyed by geological activity.
What is Classification?
Organising living organisms into groups.
Traditionally, how have organisms been classified?
According to a system proposed in the 1700’s by Carl Linnaeus known as the Linnaean System.
How does the Linnaean system group living things?
According to their characteristics and the structures that make them up.
In the Linnaean system, what groups are they divided into?
(Smaller and smaller)
Why have scientists been able to put forward new models of classification?
As knowledge of the biochemical processes taking place inside organisms developed and microscopes improved.
In 1990, what was proposed?
Carl Woese proposed the three-domain system.
What did Carl Woese find and how?
That species thought to be closely related or in fact not as closely related as first thought.
By using evidence from new chemical analysis techniques such as RNA sequence analysis.
How are organisms split in the three-domain system?
The three domain system
Where are they found?
Organisms in this domain are primitive bacteria. Often found in extreme places such as hot springs and salt lakes.
The three domain system
There are lots...
This domain contains true bacteria like E.coli and Staphylococcus.
There are lots of biochemical differences between them and Archaea although they look similar.
The three domain system
This domain includes a broad range of organisms including fungi, plants, animals and protists.
Organisms are named according to the...
Binomial system. Each organism is given its own two part Latin name.
The first part of an organism’s name refers to...
The Genus that the organism belongs to.
Tells you information on its ancestry.
The second part of an organism’s name refers to...
Humans are known as...
The binomial system is used...
Worldwide meaning scientists in different countries/speak other languages all refer to a species by the same name - avoiding confusion.
What do evolutionary trees show?
How scientists think different species are related to each other by showing common ancestors and relationships.
The more recent the common ancestor...
The more closely related the two species - the more characteristics they share.
How do scientists work out evolutionary relationships for living organisms?
They use the current classification data e.g. DNA analysis.
How do scientists work out the evolutionary relationships for extinct species?
They use information from the fossil record.
What is the death rate from infectious bacterial diseases like?
It has fallen dramatically.
Why is the problem of antibiotic resistance getting worse?
Because of the overuse and inappropriate use of antibiotics.
The more often antibiotics are used...
The bigger the problem of antibiotic resistance becomes so doctors should only prescribe them when needed.
Do antibiotics directly cause resistance?
No - they create a situation where naturally resistance bacteria have an advantage and so increase in numbers.
What can we do, as patients, to prevent antibiotic resistance?
Take the full course - so all the bacteria is destroyed meaning none is left to mutate and develop into antibiotic resistant strains.
In farming, how is antibiotics used?
To prevent them becoming ill and to make them grow faster.
Why is it bad for farmers to give their animals antibiotics?
It can lead to the development of antibiotic resistant bacteria in animals which can spread to humans.
The increase in antibiotic resistance has...
Encouraged drug companies to work on developing new antibiotics that are effective against resistant strains.
What is wrong with the rate of development for antibiotics that are effective against resistant strains?
It is slow meaning we are unlikely to be able to keep up with the demand. It’s also very costly.
How do antibiotic resistant strains form?
Bacteria can develop random mutations in their DNA leading to changes in their characteristics e.g. being less affected by an antibiotic. This gene becomes more common.
To make matter worse, bacteria are...
So rapid at reproducing so they can evolve quite quickly.
For the bacterium, the ability to resist antibiotics is...
A big advantage - is it better to be able to survive and be able to reproduce which increases their population size.
Why are antibiotic resistant strains a problem for patients infected with them?
Because they aren’t immune to the new strain and there’s no effective treatment - they easily spread.
Are superbugs becoming more common?
What is MRSA?
A relatively common ‘superbug’ that’s really hard to get rid of.