Inheritance, Variation & Evolution Flashcards
What is DNA?
Its a polymer made up of two strands forming a double helix which is contained in a chromosome
What is the generic material of a cell composed of?
DNA
What else is dna also made up of?
Repeating units called nucleotides
What does each nucleotide consist of?
One sugar molecule, a phosphate group with one of four different bases attached to the sugar
What are the bases? What do strands of DNA consist of?
The bases are A, C, G and T
- the strands consist of alternating sugar and phosphate sections which form the backbone to the DNA strands, attached to each sugar is one of the four bases
What is each base linked to? How do the bases linked?
Each base is linked to a base on the opposite strand in the helix
- A pairs with T, and G pairs with C
What forms a amino acid?
A sequence of three bases is the code for a particular amino acid, the order of bases controls the order in which amino acids are assembled to produce a particular protein
How does coding for an amino acid work?
1) . Proteins are made in the cell cytoplasm on tiny structures called ribosomes
2) . To make proteins, ribosomes uses the code in the DNA. DNA is found in the cell nucleus and can’t move out of it as its too big. So the cell needs to get the code from the DNA to the ribosome
3) . This is done by using a molecule called mRNA, which is made by copying the code from the DNA, the mRNA acts as a messenger between the DNA and the ribosome; it carries the code between the two
4) . The correct amino acids are brought to the ribosomes in the correct order by carrier molecules
How can the structure of DNA affect the protein made?
The sequence of amino acids in a protein determines its function. The DNA sequence of a gene determines the amino acid sequence of the resulting protein. Therefore, any changes in DNA sequence can result in changes im protein function -> a mutation.
What happens when a chain of amino acids has been assembled?
It folds into a unique shape which allows the protein to perform the job its meant to do
What are the three examples of proteins?
1) . Enzymes - act as biological catalysts to speed up chemical reactions
2) . Hormones - used to carry messages around the body eg insulin
3) . Structural proteins - are physically strong eg collagen is a structural protein that strengthens connective tissue
What are mutations?
They’re random changes in the sequence of bases, they occur spontaneously and continuously
What dont most mutations do?
Dont alter the protein, or they only alter it slighty so that its appearance ot function is not changed
What do other mutations code for?
They code for an altered protein with a different shape. A enzyme may no longer fit the substrate binding site or a structural protein may lose its strength.
What happens in an insertion?
Where a new base is inserted into the code, where it shouldn’t be. This changes the way the groups of three bases are ‘read’, which can change the amino acids they code for
What happens in a deletion?
Deletions are when a base is randomly deleted from the DNA sequence. This changes the triplet codes, meaning that different amino acids may be produced
What do insertions and deletions both do?
Both may change the initial amino acid its coded for, they also have a knock on effect meaning that the base sequences after the mutation are also affected
What happens in a substitution?
When a base is randomly changed to a different base
What do the parts that dont code DNA for proteins do?
They can switch genes on and off, so variations in these codes of DNA may affect how genes are exposed
What is the genome of a organism?
The entire genetic material of that organism
By understanding the human genome what does it allows scientists to do?
1) . Identify genes in the genome that are linked to different types of disease
2) . Knowing which genes are linked to inherited disease could help us to understand them better & develop effective treatments for them
3) . Trace human migration patterns from the past
What is sexual reproduction?
Where the genetic information from two organisms is combined to produce offspring which are genetically different to either parent
In humans what do both the mum and dad produce?
Produce gametes which are sex cells
What does each gamete include?
24 chromosomes, when they fuse together there are 36 chromosomes which is the correct amount to create a person!
What is variation?
The differnces in the characteristics of individuals in a population
- the mixture of genetic information from both parents produces variation in the offspring
What is asexual reproduction? What does it occur in
Needs only ome parent, so as there’s only one parent there is no fusion of gametes and no mixing of genetic information
- occurs in bacteria, fungi and plants
What is the result of asexual reproduction?
The offspring are genetically identical to the parent and each other, they are clones
In the Mid-19th century what did Mendel do?
Carried out breeding experiments on plants, one of his observations was that the inheritance of each characteristic is determined by units that are passed on to descendants unchanged.
- in late 19th century behaviour of chromosomes during cell division was observed too
What was observed by Mendel 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
What was observed by Mendel in the mid 20th century?
The structure of DNA was determined and the mechanism of gene function worked out
Why was it until after Mendel’s death people realised how significant his work was?
His work was new to the day, scientists had no background information to properly understand his findings, they didnt know what DNA, genes and chromosomes were
What did Mendel’s experiment of the peas consist of?
Mendel bred red flowered pea plants with white flowered pea plants, all of the offspring produced had red flowers
What were the results of Mendel breeding the pea plants together?
Most of the new offspring had red flowers but some also had white
What are the genes for the red and white flowers?
Red -> dominant
White -> recessive
- each plant had two genes (alleles) the control the flower colour
What is an allele?
When a gene can exist in more than one form eg eye colour
What is a chromosome?
A DNA molecule that is contained in the cell nucleus
What is a gene?
A short sequence of DNA
What is a dominant allele?
A allele that alwayd shows, as long as there is one copy from one parent in order to express characteristics
What is a recessive allele?
A allele that only shows if there are two copies, one from each parent in order to express characteristics
What is homozygous?
Two identical alleles
What is heterozygous?
Two different alleles
What is a genotype?
Set of genes in our DNA
What is a phenotype?
The physical characteristics resulting from the gene
How did Darwin propose the ‘Theory of evolution by Natural Selection’?
As a result, of observations on a round the world expedition, backed by years of experimentation and discussion; linked to developing knowledge of geology and fossils lead to the theory.
What three principles was the theory of evolution by natural selection based on?
1) . Individual organisms of a species shows a wide range of variation for a characteristic
2) . Individuals with characteristics most suited to the environment are more likely to survive to breed successfully
3) . The characteristics that have enables these individuals to survive are then passed on to the next generation
What Darwin publish his ideas in?
‘On the origin of Species (1859)’. There was much controversy surrounding these revolutionary new ideas
Why wasn’t Darwin’s theory accepted?
1) . The theory challenged the idea that God made all the animals and plants live on Earth
2) . There was insufficient evidence at the time the theory was published to convince many scientists
3) . The mechanism of inheritance and variation was not known until 50 years after the theory was published
What do we know about Natural selection?
- there is variation amongst individuals in a species
- some individuals possess characteristics that help them to survive
- they achieve reproductive success
- genes are passed on and increase the population
What was Jean-Baptiste Lamarack’s theory?
Based on the idea that changes that occur in an organism during its lifetime can be inherited.
- we know now that vast majority of cases this type of inheritance cannot occur
Why was Lamarack’s hypothesis rejected?
His experiments didn’t support his hypothesis
What supported Darwin’s idea/theory?
Discovery of genetics supported his idea as it provided an explanation of how organisms born with beneficial characteristics can pass them on.
- evidence from fossil records supported gradual changes of ‘evolution.’
- the development of antibiotic resistance in bacteria futher supported natural selection
What are fossils?
The remains of organisms from millions of years ago, which are formed in rocks
How may fossils be formed?
1) . From parts of organisms that have not decayed because one or more of the conditions needed for the decay are absent
2) . When parts of the organism are replaced by minerals as they decay
3) . As preserved traces of organisms such as footprints, burrows and rootler traces
What were many of the early forms of life?
They were soft bodied, which means that they have left a few traces behind. What traces were left have been mainly destroyed by geological activity. -> this is why scientists cannot be certain about how life began on earth.
What can we learn from fossil fuels?
How much or how little different organisms have changed as life developed on earth
What are the hypothesis’ for how life began?
- first life forms came from a swamp under the sea on earth
- organic material evolved from comets that landed on earth
Why can hypothesis’ that suggest how life began be supported?
- lack of valid evidence
1) . Many life forms were soft bodied and soft tissue tends to decay away completely-> so fossil record is incomplete
2) . Fossils that did form from millions of years ago may have been destroyed by geological activity
What are the main of Darwins theory of evolution by natural selection?
1) . Individuals compete for resources eg food
2) . Individuals in a population show variation due to sexual reproduction
3) . Individuals with characteristics best suited to the environment survive to reproduce
4) . ‘Successful’ characteristics are inherited by the offspring
5) . Species unable to compete eventually become extinct
What is extinction?
Extinction occurs when there’s no remaining individuals of a species still alive
What are the biological causes of extinction?
- increased predation
- new disease
- habitat destruction
- hunting/fishing
- competition with others for food/mates
- isolation/speciation
What are the physical causes of extinction?
- volcanic activity
- ice age
- flooding
- changes to temperature (global warming)
- drought
- asteroid collision
Who is alfred russel wallace?
- wallace independtly proposed the theory of evolution by natural selection and published his joint writings with darwin in 1858 a year later, which prompted darwin to publish ‘on the origin of species’ (1859) the following year
What is Alfred wallace russell most known for?
His work on warning colouration in animals and his theory of speciation, which withe more evidence over time has led to our current understanding of the theory of speciation
How does speciation occur?
1) . Population becomes separated due to geological processes
2) . Each population shows genetic variation as they have a wide range of alleles
3) . Environmental pressures allows individuals wirh characteristics that are better adapted to survive - survive and breed successfully
4) . New species evolve that are infertile due to adaption by natural selection
What is selective breeding?
Selective breeding (artificial selection) is the process bt which humans breed plants and animals for particular genetic characteristics
What is the process of selective breeding?
1) . Out of the exisiting stock of animals/plants you select the individuals with the most desirable characteristic
2) . Breed the male and female together
3) . From the offspring, those with the desired characteristics are bred together
4) . This continues over many generations until all of the offspring show the desired characteristic
What are the advantages of selective breeding?
- increase in the yield and health of crops or plants
- more profit for farmer/sellers
- domesticated pets have a good temperament
- decorative, large bright flowers/plants
- edible crops from wild flowers
What are the disadvantages of selective breeding?
- reduces the amount of variation in a population as you’re breeding from a reduced number of favourite individuals which leads to reducing gene pool or inbreeding
- less disease resistance if one individual is susceptible to a disease they all may be
- increased chance of harmful genetic defects being passed on
What are the characteristics that people want for selective breeding?
- disease resistance in crops
- animals which produce more meat or milk
- domestic dogs with a gentle nature
- large or unusual flowers
Traditionally how are all things classified?
Into groups depending on their structure and characteristics in a system developed by carl linneaus, who classified things into kingdom, phylum, class, order, family, genus and species
What is the binomial system?
A two part latin name that every organism has.
The first part refers to the genus that the organism belongs to and the last part refers to the species
Why were new models of classification proposed?
Evidence of internal structures became more developed due to improvements in microscopes, and the understanding of biochemical processes progressed
Why is there now a three domain system?
Developed by Carl woese due to evidence available from chemical analysis
What is the three domain system divided into?
1) . Archaea - primitive bacteria usually living in extreme confidence
2) . Bacteria - true bacteria
3) . Eykaryota - includes protists, fungi, plants and animals
Why are evolutionary trees used by scientists?
To show how they believe organisms are related. They use chrrent classification data for living organisms and fossil data for extinct organisms
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 is the process of genetic engineering?
1) . Identify the gene responsible for the desired characteristic
2) . Isolate and cut out the gene using enzymes
3) . Transfer the gene to vector usually bacteria plasmid or virus
4) . Vector is used to insert the gene into the hosts required cells
5) . Genes are transferred to the cells of the organism at an early stage of development so that they develop with the desired characteristic
How have plants and bacteria cells been genetically engineered?
Plants - to be resistant to diseases or to produce larger fruits
Bacterial cells - to produce useful substances such as human insulin to treat diabetes
What are crops that have been genetically engineered called?
Genetically modified crops, they include ones that are resistant to insect attacks or herbicides
What are the advantages of GM crops?
- increase yield
- increase profit
- in developing countries GM foods could be produced to contain vital nutrients
What are the disadvantages of GM crops?
1) affect number of wild flowers - reducing farming biodiversity
2) unsafe to eat? Humans havent fully explored the effect of eating them on human health
3) transplanted genes may get out to natural environment
What are the advantage and disadvantage to genetic engineering?
A:
- could solve many problems eg treating diseases and more efficient food production
D:
- changing an organisms gene may accidentally create unplanned problems which could get passed on
What is modern medical research exploring the possibility of?
Genetic modification to overcome some inherited diseases
How plants cloned by tissue culture?
Uses a small grouo of cells that are put into a growth medium with hormones, that produces identical new plants
- important for preserving rare plant species or comercially in plant nuseries
How are plants cloned with cuttings?
- an older and simpler method where the gardner takes cutting from good parent plants to produce many new identical plants
- cheap and quick
How do you make animal clones using embryo transplants?
Involves splitting apart artificially fertilised cells from a developing animal embryo (clones) before they become specialised
- then the identical embryos are transplanted into host mothers, it produces many ‘ideal’ offspring from the ‘best’ animals
How does adult cell cloning work?
1) . Nucleus is removed from unfertilised egg cell
2) . Nucleus from an adult body cell eg skin cell is inserted into egg cell
3) . An electric shock stimulates the egg cell to divide to form an embryo
4) . These embryo cells contian the same genetic information as an adult skin cell
5) . When embryo has developed into a ball of cells, its inserted into the womb of an adult female to continue its development, its a clone
What are the advantages of cloning?
1) study of animal clones has led to greater understanding of the development of an embryo, ageing and sge related diseases
2) . Helps preserve endangered species
What are the disadvantage of cloning?
1) reduced gene pool - fewer alleles in a population, if theres a new disease they could all be wiped out and there may be no allele in the population giving resistance to it
2) cloned animals may not be as healthy as normal ones
what does meiosis do?
it halves the number of chromosomes in gametes
describe the process of meiosis?
- before the cell divides, it copies the genetic information
- in the first division, the chromosome pairs line up in the centre of the cell
- the pairs are then pulled apart, so each new cell only has one copy of each chromosome
- in the second division, the chromosomes line up again in the centre of the cell.
- you get four gametes, each with only a single set of chromosomes in it. each of the gametes is genetically different from the others.
why do gametes join at fertilisation?
they join to restore the normal number of chromosomes, the new cell divides by mitosis, the number of cells increases as the embryo develops cells differentiate
what are the advantages for asxual reproduction?
- only needs one parent
- uses less energy than sexual reproduction, as organisms don’t have to find a mate
- its faster
- many identical offspring can be produced when conditions are favourable
what are the advantages for sexual reproduction?
- 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
how do malaria, fungi and plants reproduce?
- malarial parasites reproduce asexually in human host, but sexually in the mosquito
- fungi reproduce asexually by spores but also asexually to give variation
- plants produce seeds sexually, but also asexually by runners such as strawberry plants, or bulb division in daffodils
what is cystic fibrosis and polydactyl caused by?
- cystic fibrosis is a disorder of the cell membrane and is caused by recessive allele
- polydactyl is a disorder in which you are bor with extra fingers or toes, its caused by a dominant allele
what are the pros and against for embryonic screening?
FOR:
- will help people stop suffering
-treating disroders cost the government a lot of money
- there are laws to stop it going too far such as you cannot choose the sex of their baby
CONS:
- it implies that people with disorders are undesirable which leads to prejudice
- there may come a point where people may screen babies for desired characteristics
- its expensive
What do mutations of bacterial pathogens produce?
They produce new strains, some might be resistant to antibiotics and so are not killed. They survive and reproduce so the population of the resistant strain rises, the resistant strain will then spread because people are not immune to it and there’s no effective treatment
How can you reduce tge rate of development of antibiotic resistant strains?
- doctors shouldn’t prescribe antibiotics inappropriately such as treating non serious or viral infections
- patients should complete their course of antibiotics so all bacteria killed and none survive to mutate and form resistant strains
- the agricultural use of antibiotics should be restricted, as they can spread to humans during meat production
What is the disadvantage of antibiotics?
Its costly and slow, it’s unlikely to keep up with the emergence of new resistant strains
