meiosis and stuff Flashcards
What is meiosis?
Meiosis occurs when sex cells (gametes) are formed in the ovaries and testes.
what happens during meiosis
4 gametes are produced from one daughter cell
Each gamete has half the number of chromosomes as the parent cell (in humans, 23 chromosomes, not 23 pairs)
its important to produce gametes with half the chromosome number because Human body cells need 46 chromosomes. If each gamete contained 46, after fertilisation, body cells would contain 92 chromosomes (not viable). By halving the number in meiosis, after fertilisation each cell has the correct number of chromosomes
interphase
DNA duplicates - this means that each chromosone now consists of 2 sister chromatids
2 chromosones
1 chromatids each
prophase 1
Nuclear membrane disappears
homologus chromosones (which code for the same thing) pair up - Crossing over occurs - this meaans that non-sister chromatids exchange some genetic material CREATING VARIATION
Spindle fibres form
2 chromosones
2 chromatids each
metaphase 1
Homologous chromosome pairs line up along the equator of the cell.
Spindle fibres attach to the chromosomes at the centromere
2 chromosones
2 chromatids each
anaphase 1
2Homologous chromosome pairs are pulled apart to opposite poles – the 2 sister chromatids stay together.
Any swapped genetic material is pulled apart too. This creates genetic differenciation
2 chromosones
2 chromatids each
telophase 1 & cytokinesis
snuclear membranes form around the now divided genetic material.
After cytokinesis, 2 daughter cells are formed WITH HALF THE CHROMOSOME NUMBER OF THE PARENT CELL.
Each chromosome still consists of 2 chromatids, but the chromosome number is half of the original cell
1 chromosones
2 chromatids each
prophase 2
Nuclear membrane disappears
Spindle fibres form
1 chromosones
2 chromatids each
metaphase 2
chromosomes (still consisting of chromatids) line up along the equator.
Spindle fibres attach to the chromosome at the centromere
1 chromosones
2 chromatids each
anaphase 2
chromatids are pulled apart towards opposite poles by spindle fibres
1 chromosones
2 chromatids each
telophase 2 & cytokinesis
nuclear membranes form around the now divided genetic material
Post-cytokinesis four daughter cells are formed. Each is genetically different to one another, and different to the parent cell.
Each daughter cell also has half the chromosomes number of the parent cell – haploid
1 chromosones
1 chromatids each
Sexual reproduction
Sexual reproduction is where genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different to either parent.
This involves the fusion of male and female gametes. Because there are two parents, the offspring contain a mixture of their parents’ genes and are genetically different to their parents.
Gametes
In sexual reproduction the mother and father produce gametes by meiosis - e.g. egg and sperm cells in animals. In humans, each gamete contains 23 chromosomes half the number of chromosomes in a normal cell. (Instead of having two of each chromosome, a gamete has just one of each.)
This is why the offspring inherits features from both parents - it’s received a mixture of chromosomes from its mother and its father (and it’s the chromosomes that decide how you turn out). This mixture of genetic information produces variation in the offspring.
Asexual reproduction
In asexual reproduction there’s only one parent so the offspring are genetically identical to that parent. Asexual reproduction happens by mitosis - an ordinary cell makes a new cell by dividing in two. The new cell has exactly the same genetic information as the parent cell - it’s called a clone.
Advantages of sexual reproduction
Produces variation - If the environment changes, variation gives a survival advantage by natural selection
disadvantages of sexual reproduction
Can be time consuming and energy inefficient
Advantages of asexual reproduction
There only needs to be one parent. This means that asexual reproduction uses less energy than sexual reproduction, because organisms don’t have to find a mate. This also means that asexual reproduction is faster than sexual reproduction.
Another advantage is that many identical offspring can be produced in favourable conditions.
disadvantages of asexual reproduction
If all offspring are identical, they could all be at risk, e.g. if a new disease develops
rerproduction with both sexual and asexual reproduction
fungi, malarial parasites and some plants can do both sexual and asexual reproduction.
Fungi
Fungi are made of masses of threads called hyphae (haploid)
In ideal conditions, fungi produce spores asexually. Spores disperse and germinate to produce clones of the parent
When conditions are not good, hyphae from 2 different fungi join to create a diploid hypha (sexual reproduction). The diploid hypha undergoes meiosis to produce haploid spores. These spores will be different to spores of either of the original parents
Plants e.g. strawberries
Sexually – gametes combine in pollination to form diploid seeds that germinate to produce a new plant. It will be genetically different to either parent
Asexually – can produce ‘runners’, that will create genetically identical plants. Can still produce new plants even is flowers are destroyed in frost, are eaten or are not pollinated.
Malarial parasite
Malaria is caused by a parasite that’s 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 it’s in the mosquito and asexually when it’s in the human host
Chromosomes
long Thread-like structures in the nucleus of a cell that contain DNA
DNA double helix
Shape of the DNA. 2 strands of nucleotides that wind up around each other like a twisted ladder to protect the bases.
DNA
DNA stands for deoxyribonucleic acid. It’s the chemical that all of the genetic material in a cell is made up from. It contains coded information - basically all the instructions to put an organism together and make it work. So it’s what’s in your DNA that determines what inherited characteristics you have and its sequence determines how our bodies are made.
Gene
Section of DNA found on a chromosone that contains the instructions for a particular characteristic.
DNA bases
Four chemicals found in DNA that make up the base sequence (A, T, C, G)
Genetic code
The sequence of bases within the DNA that ultimately codes for proteins
Structure of DNA - nucleotides
DNA is made up of a series of repeated units called nucleotides. Therefore, we call DNA a polymer
Structure of DNA
Each strand of DNA is made of a sugar-phosphate backbone (held together by phosphodiester bonds)
The two halves of the helix are held together by weak hydrogen bonds.
C-G = 3 H bonds
A-T = 2 H bonds
complementary base pairing
A and T always are complementary (they are always linked together on opposite strands)
C and G are complementary.
The bases consist of
A Adenine
T Thymine
G Guanine
C Cytosine
Genome
The Genome is the entire genetic material of an organism
benefits of nderstanding the human genome
Search for genes linked to different diseases
Better understand and possibly treat inherited disorders
Trace human migration patterns from prehistory - The human genome is mostly identical in all individuals, but as different populations of people migrated away from Africa, they gradually developed tiny differences in their genomes. By investigating these differences, scientists can work out when new populations split off in a different direction and what route they took.
When do Mutations occur?
Mutations occur continuously. They can occur spontaneously, e.g. when a chromosome isn’t quite replicated properly. However, the chance of mutation is increased by exposure to certain substances or some types of radiation.
Examples of mutations
Enzymes are proteins, if the shape of an enzyme’s active site is changed, its substrate may no longer be able to bind to it - see page 120.
Structural proteins like collagen could lose their strength if their shape is changed, making them pretty useless at providing structure and support.
silent mutations (in exons - coding pieces of DNA)
Not all mutations have a serious effect. We have two copies of every gene so if one is faulty, one may be okay. Sometimes if a base is changed in the DNA it does not code for a different amino acid/protein (silent mutation). If it is coding for an enzyme it may not lose its function.
mutations (in exons - coding pieces of DNA)
Some mutations change the DNA base sequence, and a different
amino acid is coded for, so we get a different protein. If this is an enzyme, it may mean it is not folded correctly (it would alter the intermolecular forces holding it in its 3D shape). This means the shape of the active site may be incorrect, so the enzyme doesn’t work.
mutations in body cells
If a mutation occurs in a body cell it may lead to cancer.
mutations in gametes
If a mutation occurs in the egg or sperm it can lead to the offspring having a genetic disorder
mutations (in introns - non-coding pieces of DNA)
mutations in introns could cause the gene to be switched on or off when it should not be. This would affect how genes are expressed.
E.g. we might get no protein synthesis when we need it, or we could get proteins made unnecessarily. Why may this be bad?
- We may lack a protein we need
- We may make a protein when we don’t need it. If this is an enzyme it
may catalyze a reaction we don’t want to happen, or simply waste energy making proteins we do not need.
introns
Introns are non-coding pieces of DNA – but they are used in gene expression. They ‘switch on’ genes, meaning they control whether their respective exon needs to undergo protein synthesis.
Cystic fibrosis - what is it?
Cystic fibrosis is an inherited disorder of the cell membranes. It results in the body producing a lot of thick sticky mucus in the air passages (which makes breathing difficult). It also results in movement of substances in and out of a cell becoming more difficult
Cystic fibrosis - type of allele
Its caused by a recessive allele.
Therefore, the presence of two alleles will be needed
to cause the characteristic to be seen in the
phenotype . because its recessive, people with only 1 copy of the allele won’t have the disorder - they’re known as carriers - they carry the faulty allele, but don’t have any symptoms.
Polydactyly - what is it?
Polydactyly is an inherited disorder where a baby’s born with extra fingers or toes. It doesn’t usually cause any other problems so isn’t life-threatening.
Polydactyly - type of allele
Its caused by a dominant allele and so can be inherited if just one parent carries the defective allele. The parent that has the defective allele will have the condition too since the allele is dominant.
Types of embryonic screening - Pre-implantation genetic diagnosis (PGD)
During IVF, it’s possible to remove a cell from each embryo and analyse its genes. Embryos with ‘healthy’ alleles would be implanted into the mother - the ones with ‘faulty’ alleles destroyed.
Types of embryonic screening - Chorionic villus sampling (CVS)
CVS involves taking a sample of cells from part of the placenta (where the baby’s umbillical cord joins with the mothers uterus) and analysing their genes. The part of the placenta that’s taken and the embryo develop from the same original cell - so they have the same genes. If the embryo is found to have an inherited disorder, the parents can decide whether or not to terminate (end) the pregnancy.
Embryonic screening
Embryonic screening is a way of detecting inherited disorders in embryos
pros of embryonic screening
- It helps to stop people having certain inherited disorders that could negatively affect their health
- Treating disorders costs the Government (and the taxpayers) a lot of money, so screening embryos could reduce healthcare costs.
- During IVF, most of the embryos are destroyed anyway. PGD just ensures that the selected one is healthy.
cons of embryonic screening
- Implies those with genetic disorders are undesirable – could increase prejudice
- Screening embryos is expensive
- Could lead to screening to select desirable traits - e.g. they want a green-eyed, black-haired, intelligent boy.
- After PGD, the rejected embryos are destroyed-they could have developed into humans, so some people think destroying them is unethical.
- There’s a risk that CVS could cause a miscarriage. And if an inherited disorder is diagnosed through CVS, it could lead to a termination (abortion).
protein synthesis - transcription
DNA unzips (this is done using RNA polymerase enzymes & only the gene that needs transcribing is unzipped)
RNA polymerase binds to and starts ‘reading’ the DNA template strand
Complementary RNA nucleotides line up alongside the DNA template strand - In RNA, the base T is replaced with U
e.g. mRNA: AGCUCA
DNA template strand TCGAGT
A single stranded copy of the DNA is made – this copy is called mRNA. We only make mRNA of the genes that we need – not the whole DNA strand. (The double stranded DNA is too large to leave the nucleus so a smaller single stranded mRNA is needed to fit through the nuclear membrane)
Once the mRNA is made, it is released from the DNA, and the DNA reforms the double helix
The introns (non-coding regions) are cut out
mRNA leaves the nucleus and moves to the ribosomes in the cytoplasm
protein synthesis - transalation
mRNA binds to the ribosomes.
Here, the ribosome reads the mRNA in groups of 3 bases – a triplet (codon). 3 bases codes for 1 amino acid
Carrier molecules (tRNA) with the complementary base sequence to the mRNA triplet bind to the mRNA at the ribosome. Attached to the other end of the carrier molecule is an amino acid.
The next three bases are read and another carrier molecule (with a complementary base sequence to the mRNA) brings in another amino acid
A peptide bond forms between the amino acid. The first carrier can now leave.
A third amino acid is brought in by another carrier molecule, which forms a peptide bond to the growing chain.
Once all the mRNA has been read, we are left with a sequence of amino acids. We call this a polypeptide chain (primary structure).
It can then fold into a 3D shape
Factors to assess in sexual asexual reproduction qns
Type of reproduction - sexual/asexual
Type of cell division - meiosis/mitosis
No of parents - 2/1
Is there variation - yes/no
What are alleles?
All genes exist in different versions called alleles. Gametes only have one allele of each gene, but all the other cells in an organism have two one on each chromosome in a pair. This is because we inherit half of our alleles from our mother and half from our father. In genetic diagrams, letters are usually used to represent alleles.
TT
Homozygus dominant
Tt
hetrozygus
tt
Homozygus recessive
dominant needs…
at least 1 copy of the dominant allele
Dominant musks recessive
Recessive needs…
at least 2 copies of the recessive allele
Sex chromosomes
There are 23 pairs of chromosomes in every human body cell. Of these, 22 are matched pairs of chromosomes these just control your characteristics. The 23rd pair are labelled XY or XX. They’re the two chromosomes that decide your sex whether you turn out male or female.
Male genotype
Males have an X and a Y chromosome: XY
The Y chromosome causes male characteristics.
Female genotype
Females have two X chromosomes: XX
The XX combination allows female characteristics to develop.
if the recessive disease allele is on the y chromosone…
only males can get it because only males have the Y chromosones.
if the recessive disease allele is on the x chromosone then for the male…
Whatever allele is on the x chromosone of the male is inherited. If its recessive there is no opportunity for it to be musked by a dominant
if the recessive disease allele is on the x chromosone then for the female…
There are 2 x chromosones so the only way to get the disease is for it to be rr to not get the disease it can be RR or Rr
Variation
differences in the characteristics of individuals in a population
interspecific variation
There are many variations between organisms that belong to different species. These differences can help us to classify them.
Intraspecific variation
Organisms that are in the same species also show variation, although they will always have more in common with each other than they will with members of another species.
examples of variation caused by the environment
Hair colour and length
Language
Scars
Tattoos
examples of variation caused by genes
Blood group
Eye colour
Natural colour of hair
Shape of earlobe
examples of variation caused by both the environment and genes
Height
Skin colour
Weight
Sporting achievements
continuous variation
Properties:
- No distinct categories
- No limit on the value
- Tends to be quantative
Examples:
- Height
- Weight
- heart Rate
- Finger length
- leaf length
continuous variation is represented by a line graph
discontinuous variation
Properties:
- distinct categories
- No in between categories
- Tends to be qualitative
Examples:
- Tongue rolling
- finger prints
- eye color
- blood groups
discontinuous variation is represented by a bar graph
What 3 processes can lead to genetic variation
Meiosis -crossing over
Sexual Reproduction - random fertilisation
Mutations
Evolution
Evolution is described as a ‘change in the inherited characteristics of a population over time through a process of natural selection.’ Evolution may result in the formation of a new species.
The theory of evolution states that the species alive today have evolved from simple life forms that first developed more than 3 billion years ago
Evolution requires three ‘ingredients’?
1. Variation
2. Selection
3. Time
Larmarck’s theory
Within a species, organisms all start off looking very similar
Some individuals would change as a result of use or disuse of a part of the body
e.g. repeated use of an arm would increase its size. This gives the individual an acquired characteristic
Offspring would inherit their parent’s acquired characteristics (the trait is inherited by the offspring) and develop it further
Eventually, over time, the environment would have directly affected individuals so changing the nature of the species
similar
change- use/disuse
inherit acuired charicteristic from parent
Charles Darwin - theory of evolution - natural selection
1) Within a species, there is always variation
2) A random, chance mutation occurs that alters the genotype and the phenotype of some individuals
3) Those with the mutation (altered phenotype) have a survival advantagein that particular environment
4) These individuals are more likely to survive, reproduce and pass on the gene for the desirable characteristic to their offspring. It is an inherited characteristic.
5) Over time, the ‘mutated’/new phenotype becomes the normal.
6) This is called natural selection. Nature is effectively selecting the organism with the most useful genes.
Wallace and Warning colouration
Use of brightly colours to deter predators
Predators learned to avoid animals with these colourations – they are likely to taste bad, be poisonous or cause injury
Wallace realised warning colouration must be passed on by natural selection
Wallace’s ideas led to our modern understanding of mimicry
Alfred Russel Wallace
During his career, Wallace independently came up with the idea of natural selection and published work on the subject together with Darwin in 1858. This then prompted Darwin to publish ‘On the Origin of Species’ in 1859.
species
A species is groups of organisms which have similar characteristics, and can successfully breed with each other (interbreed) to produce fertile offspring.
If a donkey and a horse mate then a mule is produced.
A mule is infertile. A donkey and horse are separate species.
Why may mules be infertile?
Speciation
Formation of a new species over a long period of time, through separation of a population
Speciation - Isolation Mechanisms
Continental drift (islands splitting apart)
Mountain formation
Splitting of habitats
Building of roads
Deforestation
speciation - process
A population becomes geographically isolated from the original population.
E.g. by continental drift or a mountain.
The new population is exposed to different environmental conditions e.g. different habitats or food sources on the other side of the mountain.
Mutations may occur, creating variation in the new population, there will be new phenotypes.
**Natural selection **occurs, whereby the best adapted individuals in the new population survive and reproduce. Others will not survive
Over a long period of time the new population changes to the point where it can no longer interbreed with the old population to give fertile offspring.
Speciation has occurred.
geog isolated
different conditions
mutations - variation
natural selection
cant breed w old population
fossil
A fossil is the remains of organisms that lived millions of years ago
ways fossils can form
- mineral replacement - hard body parts, such asbones and shells, which do not decay easily or are replaced by minerals as they decay
- parts of organisms that have not decayed because one or more of the conditions needed for decay are absent. For example,dead animals and plantscan be preserved inamber, peat bogs, tar pits, or in ice
- preserved traces of organisms, such asfootprints,burrowsand rootlet traces - these become covered by layers ofsediment, which eventually become rock
ways fossils can form - mineral replacement
- An organism dies and sinks to the bottom of the water
- The organism becomes covered in sediment, the soft parts of the body decay, the sediment begins to turn to rock.
- More sediment settles, more organisms die and the sediment is compressed as more layers are added. Minerals replace the bone and the skeleton turns to rock.
- Rock layers become lifted up, they are eroded by wind and rain, faults in the rocks expose the fossils.
ways fossils can form - preserved traces
As preserved traces of organisms, such as footprints, burrows and rootlet traces can be buried under layers of sediment that eventually become rock
parts of organisms that have not decayedways fossils can form - parts of organisms that have not decayed
Whole insects or plant parts become trapped in resin/sap from a tree
The resin must fall into water and become covered in sediment (oxygenless)
Organisms can also be preserved in ice
Volcanic ash can cover a tree branch and prevent it from decaying
Evidence from the fossil record
As each layer of rock is added the one on top must be younger than the one below so we can tell the relative ages of rocks.
It also shows us how organisms that lived in the past differ from those living today
It shows us how long a species existed for – when does it disappear from the fossil record?
Why is the Fossil record incomplete?
- Fossils are formed under very specific conditions. The remains of the organisms are usually washed into water and buried by the mud or silt. If there is any oxygen at all, the remains would decay and there would be nothing left.
- The hard parts of the organism are replaced by minerals. If an organism is completely soft bodied like an earthworm, there are no hard parts and a fossil will not be formed. It is a very rare event for all these conditions to be met.
- Finally the fossils need to be found. They are usually in rocks beneath the sea or river bed, or brought to the surface by tectonic plate movement. Only weathering and erosion can expose them here, which takes a long time.
Extinctions
Extinctions occur when there are no remaining individuals of a species still alive…
What might cause a species to become extinct?
Changes to the earths environment is believed to have caused the dinosaurs to become extinct, other reasons
Illegal wildlife trade
Overfishing
Exponential population growth
Overconsumption
Pollution
Destruction of natural habitats / Habitat loss
Climate change
Invasive or alien species (be new predators, competition for food or introducing new diseases)
Classification
Classification is the grouping of organisms according to differences and similarities in their structure and characteristics
5 kingdom system
Linnaeus created the 5 kingdom system. Below kingdom there are smaller subdivisions…
As you descend the classification system, organisms grouped within it get more similar.
Traditionally, organisms have been classified according to a system first proposed in the 1700s by Carl Linnaeus, which groups living things according to their characteristics and the structures that make them up.
In this system (known as the Linnaean system), living things are first divided into the 5 kingdoms (e.g. Animals, plants, Fungi, Protists, Prokaryotes). The kingdoms are then subdivided into smaller and smaller groups - phylum, class, order, family, genus, species.
Binomial system
In the binomial system, every organism is given its own two-part Latin name.
The first part refers to the genus that the organism belongs to. This gives you information on the organism’s ancestry. The second part refers to the species. They are written in italics and the genus starts with a capital letter
e.g - Humans are known as Homo sapiens. Homo is the genus and ‘sapiens’ is the species.
The binomial system is used worldwide and means that scientists in different countries or who speak different languages all refer to a particular species by the same name avoiding potential confusion.
three-domain system
n 1990, Carl Woese proposed the 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 - Archaea & bacteria
In the three-domain system, organisms are first of all split into three large groups called domains:
- Archaea
Organisms in this domain were once thought to be primitive bacteria, but they’re actually a different type of prokaryotic cell. They can be found in extreme places such as hot springs and salt lakes.
- Bacteria
This domain contains true bacteria like E. coli and Staphylococcus. Although they often look similar to Archaea, there are lots of biochemical differences between them.
- Eukaryota
This domain includes a broad range of organisms including fungi, plants, animals and protists (page 136).
These are then subdivided into smaller groups kingdom, phylum, class, order, family, genus, species.
Evolutionary trees
Evolutionary trees show how scientists think different species are related to each other.
They show common ancestors and relationships between species. The more recent the common ancestor, the more closely related the two species and the more characteristics they’re likely to share.
Scientists analyse lots of different types of data to work out evolutionary relationships. For living organisms, they use the current classification data (e.g. DNA analysis and structural similarities). For extinct species, they use information from the fossil record
process of selective breeding
- Animals within a population show genetic variation. Humans select two individuals that have the required characteristics - e.g. speed.
2.These individuals are allowed to mate; if they are from different breeds this is known as cross-breeding.
3.When the offspring are produced the ones with the most desirable characteristics are chosen and mated
4.This happens for many generations until the animal with all the right characteristics is produced.
What is selective breeding?
Selective breeding is when humans artificially select the plants
or animals that are going to breed so that the genes for particular
characteristics remain in the population. Organisms are
selectively bred to develop features that are useful or attractive:
e.g.
. Animals that produce more meat or milk.
. Crops with disease resistance.
· Dogs with a good, gentle temperament.
· Decorative plants with big or unusual flowers.
process of selective breeding - adapted for increaseed milk yield
A breeder selects the individual from the group with most muscle
Offspring are produced from the chosen parents
Some of the offspring are more muscular than others
Most muscular offspring are selected (after checking that they are healthy) and bred together to produce offspring
An increased number of the population will be muscular
selective breeding - Reducing the gene pool
The main problem with selective breeding is that it reduces the gene pool - the number of different alleles (forms of a gene) in a population. This is because the farmer keeps breeding from the “best” animals or 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. Some dog breeds are particularly susceptible to certain defects because of inbreeding - e.g. heart disease is common in boxer dogs.
There can also be serious problems if a new disease appears, because 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.
Benefits of selective breeding
Produces individuals with desired characteristics
New varieties may be economically important
Animals can be selected that cannot cause harm, for example cattle without horns
risks of selective breeding
Inbreeding will reduce variation (reduced gene pool)
Reduced genetic variation can lead to disease susceptibility of all offspring, which could be extremely destructive
rare disease genes can be unknowingly selected as part of a positive trait, leading to problems with specific organisms, e.g., a high percentage of Dalmatian dogs are deaf
selective breeding - plants
Selective breeding is also used to produce new plant varieties. Plants may be bred for their:
* disease resistance
* Increased yield
* Increased quality
* Quick growing and mature quickly
* Have a distinctive taste, aroma and or color
* Have a long shelf life, store well or can be frozen
cloning plants
There are two main methods for cloning plants:
Taking cuttings – original method
Tissue culture – more modern method
cloning plants -Taking cuttings
- Choose the parent plant with the most desirable charicteristics
- cut a small section of the plant e.g. Shoots, sections of stems
- trim the end - make sure the equipment is clean to avoid infection by microbes
- dip it in hormonal rooting powder to encourage root growth
- plant in moist compost & keep in humid atmosphere until roots develop to reduce water loss through leaves
cloning plants - Tissue culture
- Take a few cells from a plant.
- Grow them with ‘plant hormones’ to stimulate them to divide.
- Grow in different hormones to stimulate them to grow into small plants.
- Expensive but you can grow thousands of plants from a small amount of tissue.
- Guarantees the plants you grow have the characteristics you want.
cloning animals - embryo transplants
Farmers can use embryo transplants to produce cloned offspring from their best bull and cow:
- 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.
- These cloned embryos can then be implanted into lots of other cows…
- where they grow into calves (which will all be genetically identical to each other).
cloning animals - Adult cell cloning
Adult cell cloning can also be used to make animal clones. Adult cell cloning involves taking an unfertilised egg cell and removing its nucleus. The nucleus is then removed from an adult body cell (e.g. skin cell) and is inserted into the ‘empty’ egg cell. The egg cell is then stimulated by an electric shock - this makes it divide, just like a normal embryo.
When the embryo is a ball of cells, it’s implanted into the uterus (womb) of an adult female (the surrogate mother). Here the embryo grows into a clone of the original adult body cell as it has the same genetic information.
Benefits of cloning
- Cloning quickly gets you lots of “ideal” offspring with known characteristics. This can benefit farmers, e.g. if a farmer has a cow that produces lots of milk, he could clone it and create a whole herd of cows that all produce lots of milk relatively quickly.
- 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.
Concerns of cloning
Cloning gives you a “reduced gene pool” - this means there are fewer different alleles in a population. If a population are all closely related and a new disease appears, they could all be wiped out no allele in the population giving resistance to the disease.
It’s possible that cloned animals might not be as healthy as normal ones, e.g. Dolly the sheep had arthritis, which tends to occur in older sheep (but the jury’s still out on if this was due to cloning).
Some people worry that humans might be cloned in the future. If it was allowed, any success may follow many unsuccessful attempts, e.g. children born severely disabled. Also, you’d need to consider the human rights of the clone - the clone wouldn’t have a say in whether it wanted to be a clone or not, so is it fair to produce one?
Antibiotic resistance
Like all organisms, bacteria sometimes develop random mutations in their DNA. These can lead to changes in the bacteria’s Characteristics, e.g. being less affected by a particular antibiotic. This can lead to antibiotic-resistant strains forming as the gene for antibiotic resistance becomes more common in the population.
To make matters worse, because bacteria are so rapid at reproducing, they can evolve quite quickly.
For the bacterium, the ability to resist antibiotics is a big advantage. Non-resistant bacteria will be killed by antibiotics, but a resistant bacterium is better able to survive, even in a host who’s being treated to get rid of the infection. This means it lives for longer and reproduces many more times. This increases the population size of the antibiotic-resistant strain.
Antibiotic-resistant strains are a problem for people who become infected with these bacteria because they aren’t immune to the new strain and there is no effective treatment. This means that the infection easily spreads between people. Sometimes drug companies can come up with a new antibiotic that’s effective, but ‘superbugs’ that are resistant to most known antibiotics are becoming more common.
Examples
MRSA (methicillin-resistant Staphylococcus aureus) is a relatively common ‘superbug’ that’s really hard to get rid of. It often affects people in hospitals and can be fatal if it enters their bloodstream.
TB is a very serious lung disease caused by a bacterial infection. Multi-drug-resistant TB (also known as MDR-TB) is a form of TB that has developed resistance to multiple antibiotics, making it hard to treat. Scientists in China have reported an MDR-TB epidemic there tens of thousands of Chinese people develop MDR-TB each year.
The spread of antibiotic resistance
For the last few decades, we’ve been able to deal with bacterial infections pretty easily using antibiotics. The death rate from infectious bacterial diseases (e.g. pneumonia) has fallen dramatically.
But the problem of antibiotic resistance is getting worse partly because of the overuse and inappropriate use of antibiotics.
Examples
- Doctors prescribing antibiotics for non-serious conditions.
- Doctors prescribing antibiotics for infections caused by viruses.
The more often antibiotics are used, the bigger the problem of antibiotic resistance becomes, so it’s important that doctors only prescribe antibiotics when they really need to.
It’s not that antibiotics actually cause resistance they create a situation where naturally resistant bacteria have an advantage and so increase in numbers. If they’re not doing you any good, it’s pointless to take antibiotics - and it could be harmful for everyone else.
It’s also important that you take all the antibiotics a doctor prescribes for you. Lots of people stop taking their antibiotics as soon as they feel better, but this can increase the risk of antibiotic-resistant bacteria emerging. Taking the full course makes sure that all the bacteria are destroyed, which means that there are none left to mutate and develop into antibiotic-resistant strains.
In farming, antibiotics can be given to animals to prevent them becoming ill and to make them grow faster. This can lead to the development of antibiotic-resistant bacteria in the animals which can then spread to humans, e.g. during meat preparation and consumption. Increasing concern about the overuse of antibiotics in agriculture has led to some countries restricting their use.
The increase in antibiotic resistance has encouraged drug companies to work on developing new antibiotics that are effective against the resistant strains. Unfortunately, the rate of development is slow, which means we’re unlikely to be able to keep up with the demand for new drugs as more antibiotic-resistant strains develop and spread. It’s also a very costly process.
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
Restriction enzymes
Restriction enzymes cut open the plasmid leaving ‘sticky ends’ – one strand of the dsDNA has an overhang
genetic engineering - process
- A plasmid (vector) is obtained from within a bacterium
- It is cut open using restriction enzymes
- At the same time, the required gene (e.g. coding for the desired characteristic) is cut from the donor organism using the same restriction enzymes used to cut open the vector.
- The two sticky ends can overlap and be joined together using DNA ligase.
- This is now called recombinant DNA
- The recombinant DNA (plasmid + required gene) is inserted into a new bacterium through heat shock, or electroporation - the bacterium is now transgenic
- The transgenic organism is checked to check it is expressing the required gene. This is done by inserting a genetic marker gene which could be a fluorescence gene or an antibiotic resistance gene (i.e. if the flourescence gene is inserted, it’ll glow OR it’ll survive exposure to antibiotics). The assumption is, that if the marker gene has been inserted and expressed, so have the desired gene)
- The bacterium is allowed to divide and begins producing the desired protein (insulin)
- Insulin can be extracted and purified for use in humans
Uses of genetic engineering
Scientists use genetic engineering to do all sorts of things:
Genetically modified (GM) crops have had their genes modified, e.g. to improve the size and quality of their fruit, or make them resistant to disease, insects and herbicides (chemicals used to kill weeds).
Bacteria have been genetically modified to produce human insulin that can be used 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 treatments for inherited disorders caused by faulty genes, e.g. by inserting working genes into people with the disorder. This is called gene therapy.
The issues surrounding genetic engineering
Genetic engineering is an exciting new area in science which has the potential for solving many of our problems (e.g. treating diseases, more efficient food production, etc.) but not everyone thinks it’s a great idea.
There are worries about the long-term effects of genetic engineering that changing a person’s genes might accidentally create unplanned problems, which could then get passed on to future generations.
It’s the same with GM crops…
GM crops - Benefits
On the plus side, the characteristics chosen for GM crops can increase the yield / quality, making more food.
Quick way of obtaining desired trait/product - Faster than selective breeding
People living in developing nations often lack nutrients in their diets. GM crops could be engineered to contain the nutrient that’s missing. For example, ‘Golden Rice’ is a GM rice crop that contains beta-carotene lack of this substance causes blindness.
GM crops - Concerns
GM foods are more expensive
Limited long term testing for risks of GM foods - Not everyone is convinced that GM crops are safe and some people are concerned that we might not fully understand the effects of eating them on human health. e.g. Risk of allergic reactions for GM foods – different properties/chemicals to the original food
Risk of transgenic genes being transferred by pollinators to non-GM crops. - A big concern is that transplanted genes may get out into the natural environment. For example, the herbicide resistance gene may be picked up by weeds, creating a new ‘superweed’ variety.
Could reduce biodiversity – what if a new disease occurs?
Mycoprotein
As the population of the world increases, it’ll be important to find new food sources to add to those that currently exist. Using modern biotechnology techniques, large amounts of microorganisms can be cultured (grown) industrially under controlled conditions in large vats for use as a food source.
A fairly modern food source that is becoming increasingly popular is mycoprotein. Mycoprotein means protein from fungi. It’s used to make high-protein meat substitutes for vegetarian meals, e.g. Quorn™. A fungus called Fusarium is the main source of mycoprotein. It is grown in large vats on glucose syrup, which acts as food for the fungus.
The fungus respires aerobically, so oxygen is supplied, together with nitrogen (as ammonia) and other minerals. The mixture is also kept at the right temperature and pH. Once ready, the fungal biomass is harvested, purified and dried to make the mycoprotein. It’s then processed further by adding flavourings and other ingredients.
