P2- Inheritance, variation and evolution Flashcards
2 types of reproduction
Sexual
Asexual
What is sexual reproduction?
Genetic information from 2 organisms (mother and father) are combined to produce offspring not genetically identical to parents
How many parents are there in sexual reproduction?
2
What do the mother and father produce in sexual reproduction?
Gametes (by meiosis)
What does each gamete contain in humans?
23 chromosomes
What do the egg and sperm cells do in sexual reproduction?
Fuse together/ Fertilise to form a cell with the full number of chromosomes (half from mother and half from father)
Why do the offspring of sexual reproduction contain a mixture of their parents’ genes?
Because there are TWO parents
What does a mixture of genetic information produce?
A variation in the offspring
What is asexual reproduction?
Where there is only one parent therefore the offspring are genetically identical to that parent
How many parents does asexual reproduction involve?
1
What process does asexual reproduction happen by?
Mitosis (ordinary cell divides)
What are the new cells created by asexual reproduction to their parent?
Clones
What is produced by meiosis?
Gametes
What is meiosis?
A process involving 2 cell divisions to make gametes which only have half the original number of chromosomes
Where is the only place meiosis happens in humans?
The reproductive organs (ovaries or testes)
How many cell divisions happen in meiosis?
2
Meiosis step by step
1) DNA duplicates
2) Chromosomes line up at equator in pairs
3) Chromosomes pulled apart (some of mother, some of father= variation)
4) Chromosomes line up at equator in both cells again
5) 2nd division where arms of chromosomes are pulled apart
6) Gametes are made as 4 haploid daughter cells
4 advantages of sexual reproduction over asexual
1) Offspring have a mix of 2 sets of chromosomes= variation
2) Variation increases chances of surviving a change in environment (survival advantage)
3) More likely to breed successfully and pass genes on as their characteristics give them a better chance of survival (natural selection)
4) Can use selective breeding to speed up natural selection allowing us to produce animals with the desired characteristics. Means food production can increase
4 advantages of asexual reproduction over sexual
1) Only needs one parent
2) Uses less energy as organisms don’t need to find a mate
3) Faster than sexual
4) Many identical offspring can be produced if in favourable conditions
Can some organisms reproduce both sexually and asexually?
Yes
3 examples of organisms that can reproduce both sexually and asexually?
1) Malarial parasites
2) Fungi
3) Plants
How do malarial parasites reproduce sexually?
The parasite produces sexually when its in the MOSQUITO
How do malarial parasites reproduce asexually?
The parasite produces asexually when its in the HUMAN HOST
How does fungi reproduce sexually?
Sexually-produced spores introduce variation
How does fungi reproduce asexually?
Asexually-produced spores form fungi genetically identical to the parent fungus
How do plants reproduce sexually?
Many plants produce seeds sexually
How do plants reproduce asexually?
1) By runners (strawberry plants)
2) Bulb division (daffodils)
What does DNA stand for?
Deoxyribonucleic acid
What is DNA?
-The chemical that all genetic material in a cell is made up from
-Contains coded information
-Found in chromosomes (in the nucleus)
-It is a polymer
What does your DNA determine?
The inherited characteristics you have
What is a genome?
The entire genetic information of an organism
3 reasons why it is important to understand the human genome?
1) Allows scientists to identify genes in the genome that link to different types of diseases
2) Knowing what genes link to inherited diseases could help develop effective treatments for them
3) Scientists can look at them to trace the migration of certain populations around the world
What do DNA molecules contain?
A genetic code that determines which proteins are built
What is the monomer of DNA called?
Nucleotides
What are DNA strands?
Polymers made up of lots of repeating units called nucleotides
What does each nucleotide consist of? What shapes are each one?
- A sugar (pentagon)
-A phosphate group (circle)
-A base (square)
What are the 4 different bases of DNA?
A, T, C, G
What do the 4 different bases of DNA attach to?
One of the 4 different bases joins to each sugar
What does base A always pair up with?
T
What does base C always pair up with?
G
What is complementary base pairing?
When A always pairs with T, and C always pairs with G
What does the order of bases in a gene decide?
The order of amino acids in a protein
What is each amino acid coded for by?
A sequence of 3 bases in the gene
What are the 2 stages of proteinsynthesis?
1) Transcription
2) Translation
What is Transcription?
mRNA copy of the DNA is made in the nucleus and then mRNA travels to the ribosome where translation then takes place
What is Translation?
-Ribosome reads mRNA sequence
-tRNA molecules bring amino acids to form a polypeptide chain
-This chain then folds into a functional protein
What is Proteinsynthesis?
-Process by which cells build proteins
-Involves transcription and translation
What do the non-coding parts of DNA control?
-Whether or not a gene is expressed
-Can switch genes on or off
How do ribosomes make proteins?
They use the code in the DNA
How is mRNA made?
Copying the code from DNA
What does the molecule mRNA help do?
Acts as a messenger between the DNA and the ribosomes and carries the code between the two
What happens after a chain of amino acids has been assembled?
It folds into a unique shape which allows the protein to perform the task its meant to do
3 examples of types of proteins
1) Enymes
2) Hormones
3) Structural proteins
What are mutations in DNA?
A random change in an organisms DNA
How often do mutations occur?
Continously
What do mutations change?
The sequence of the DNA bases in a gene to produce a genetic variant
Do most mutations have a big effect on the protein?
No
How can a mutation seriously affect a protein? What might happen as a result?
-Sometimes, the mutation will code for an altered protein with a change in its shape
-Could affect its ability to perform its function
What can happen if there is a mutation in the non-coding DNA?
It can alter how genes are expressed
What is the definition of gametes?
Sex cells (sperm and egg cells)
What is the definition of chromosomes?
Structures in a cell that contain genetic material (DNA)
What is the definition of gene?
Small sections of a chromosomes that codes for a protein
What is the definition of allele?
Different forms of the same gene (e.g AA/Aa/aa)
What is the definition of dominant?
Always expressed, even if only one copy is present
What is the definition of recessive?
Only expressed if two copies are present
What is the definition of homozygous?
Same alleles
What is the definition of heterozygous?
Different alleles
What is the definition of phenotype?
Physical characteristics
What is the definition of genotype?
Genetic information
Examples of characteristics controlled by a single gene
Red/Green colour blindness
Mouse fur colour
2 examples of inherited disorders
Cystic Fibrosis
Polydactyly
What allele is cystic fibrosis caused by?
Recessive
What is cystic fibrosis?
A genetic disorder of the cell membranes causing thick sticky mucus in the lungs and pancreas
What allele is polydactyly caused by?
Dominant
What is polydactyly?
A genetic disorder where a baby is born with extra fingers or toes
3 reasons for embryonic screening
1) Help to stop people suffering
2) Treating the disorders costs the govt and taxpayers a lot of money
3) There are laws that stop it going too far e.g parents cannot select the sex of their baby
3 reasons against embryonic screening
1) Implies that people with genetic problems are ‘undesirable’
2) May come to a point where everyone wants to screen their embryos for the most desirable
3) Screening is expensive
What are the female sex chromosomes?
XX
What are the male sex chromosomes?
XY
What are species?
A group of living organisms consisting of similar individuals capable of breeding with one another to produce fertile offspring
What is variation?
The differences within a species
What are the 2 types of variation?
Genetic
Environmental
What is genetic variation?
The combination of genes an offspring gets from their 2 parents
Can characteristics be determined by both genetic and environmental variation?
Yes
What is environmental variation?
The environment (including the conditions an organism lives and grows in) can cause differences between members of the same species
What does variation arise from?
Mutations
What did Charles Darwin conclude from his findings (Survival of the Fittest)?
Organisms with the most suitable characteristics for their environment would be more successful competitors and would be more likely to survive
What is the Theory of Evolution by natural selection?
All of today’s species have evolved from simple life forms that first started to develop over 3 billion years ago
5 key elements of natural selection (for an exam q)
1) Mutation - Genetic variation
2) Application- Say why the mutation is good
3) Survival- Explain why they survive
4) Reproduce
5) Pass on allele/ mutation to their offspring
What happens if two populations of one species become so different in phenotype?
A completely new species is formed (this is called speciation)
What is Selective Breeding?
Humans artificially select the plants or animals that are going to breed so that the genes for particular characteristics remain in the population.
What is the step by step process of selective breeding?
1) Choose parents with the desired characteristics
2) Breed them together
3) Select the best of their offspring and breed them together
4) This continues over many generations so the desirable traits gets stronger and stronger until all have the characteristic
4 examples of having the desired characteristic due to selective breeding?
1) Animals that produce more meat and milk
2) Crops with disease resistance
3) Domestic dogs with good temperament
4) Large or unusual flowers
What is the problem with selective breeding?
It reduces the gene pool and therefore can lead to interbreeding. This can cause health problems as there’s more chance of the organisms inheriting harmful genetic defects
What is genetic engineering?
Transfers a gene that is responsible for a desirable characteristic from one organism’s genome to another so it also has the desired characteristic
What is the step by step process of genetic engineering?
1) Enzymes are used to isolate the required gene;
2) This gene is inserted into a vector, usually a bacterial plasmid or a virus
3) The vector is used to insert the gene into the required cells
4) 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.
Why have plant crops been genetically engineered?
To be resistant to diseases or to produce bigger better fruits.
Why have bacterial cells been genetically engineered?
To produce human insulin that can be used to treat diabetes
What are the benefits of genetic engineering?
It is an exciting area of science which has the potential for solving many problems like treating diseases and for more efficient food production
What are the risks of genetic engineering?
Changing an organism’s genes might accidentally create unplanned problems which could get passed on to future generations
What are Genetically Modified (GM) crops?
Crops engineered to be resistant to insects and herbicides
Pros of GM crops?
1) The characteristics chosen can increase the yield and make more food
2) They could be engineered to contain the nutrients that people in developing countries are lacking
3) They are already being grown in some places without any problems
Cons of GM crops?
1) May affect the number of flowers that live in and around crops
2) Not everyone is convinced they are safe and we might not fully understand the effects eating them could have on human health
3) Transplanted genes may get out in the natural environment
2 ways plants can be cloned
Tissue culture
Cuttings
What are cuttings?
Gardeners take cuttings from good parent plants and plant them to produce genetically identical copies of the parent plant
What is tissue culture?
Where a few plant cells are put in a growth medium with hormones and they grow into new plants which are clones of the parent plant
What can you use to make animal embryos?
Embryo transplants
What are embryo transplants? How do they work?
Sperm cell taken from a prize bull and egg cell taken from a prize cow. Sperm is then artificially fertilised with an egg. The embryo that develops is split many times to form clones before any cells become specialised.
What is adult cell cloning? How does it work?
It involves taking an unfertilised egg cell and removing its nucleus. The nucleus is then removed from an adult body cell and is inserted into the ‘empty’ egg cell. This is then stimulated by an electric shock which makes it divide just like a normal embryo
Benefits of cloning
-Quickly gets you lots of ideal offspring
-Could lead to greater understanding of the development of the embryo
-Help preserve endangered species from going extinct
Risks of cloning
-Reduced gene pool (new diseases)
-Expensive
-Cloned animals might not be as healthy as normal ones
3 reasons why Charles Darwin’s theory from ‘On the Origin of Species’ was controversial
1) Against common religious beliefs about how life on earth developed
2) Couldn’t explain why these new and useful characteristics appeared or how they passed on from individual organisms to their offspring
3) Wasn’t enough evidence to convince many scientists
Who was the person that had different ideas to Charles Darwin?
Jean-Baptiste Lamarck
What was Jean-Baptiste Lamarck’s opposing theory to evolution?
Changes an organism acquires during its life will be passed on to its offspring
-If a characteristic was used a lot by an organism, it would become more developed during its lifetime
Why was Lamarck’s hypothesis eventually rejected?
Experiments didn’t support his hypothesis (if a hamster was dyed pink, its offspring would still be born with brown fur)
What is speciation?
The development of a new species
What 2 factors lead to speciation?
Isolation
Mutation
What are the 4 stages of forming a new species (speciation)?
Isolation
Mutation
Natural selection
Speciation
What is isolation?
Where populations of a species are separated due to a physical barrier (e.g floods)
What is the step by step process which gives rise to new species? (speciation)
1) 2 populations of the same species
2) A physical barrier separates the populations
3) Populations adapt to the new environments
4) Development of new species
Who was Alfred Russel Wallace? What did he discover?
-Scientist at same time as Darwin
-Worked on the idea of speciation
-Came up with natural selection and published his work together with Darwin
What did Gregor Mendel experiment with?
Pea plants
What did Gregor Mendel discover?
-Characteristics in plants were passed on from one generation to the next and his results
-Eventually becoming the foundation of modern genetics
What three important conclusions did Mendel reach about herdity in plants?
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 or recessive and if an individual has both for a characteristic, the dominant one will be expressed
Why was Mendel’s discovery only recognised after his death?
Scientists of the time didn’t have the background knowledge to properly understand his findings as they had no idea about genes, DNA and chromosomes
What did scientists become familiar with in the late 1800s?
Chromosomes, they were able to observe how they behaved during cell division
What did scientists realise and discover about chromosomes and Mendel’s ‘units’?
-Striking similarities in the way chromosomes and Mendel’s “units” acted
-It was proposed that the units were found on chromosomes and now known as genes
What was determined in the mid 1900s?
The structure of DNA
2 pieces of evidence for evolution
1) Fossils
2) Antibiotic resistance in bacteria
What are fossils?
The remains of organisms from many thousands of years ago, which are found in rocks
What do fossils provide us with information about?
-The evidence that organisms lived ages ago
-Tell us a lot about how much/little organisms have evolved over time
What are the 3 ways fossils form in rocks?
1) Gradual replacement by minerals
2) From casts and impressions
3) From preservation in places where no decay happens
How are fossils found from gradual replacement by minerals?
1) Things like teeth and bones which don’t decay easily are eventually replaced by minerals as they decay
2) This forms 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
How are fossils found from casts and impressions?
1) When an organism is buried in a soft material like clay
2) The clay later hardens around it and the organism decays which leaves a cast of itself
How are fossils found from preservation in places where no decay happens?
1) In amber (clear yellow stone) and tar pits, there’s no oxygen or moisture so decay microbes can’t survive
2) In glaciers, it’s too cold for the decay microbes to work
Why is the fossil record incomplete?
Many early forms of life were soft-bodied and soft tissue tends to decay away completely
How may fossils formed millions of years ago have been destroyed?
Geological activity (e.g movement of tectonic plates crushing fossils already formed in the rock)
Why do extinctions occur?
When there are no remaining individuals of a species still alive.
5 factors that contribute to the extinction of species
1) The environment changes too quickly
2) A new predator kills them all
3) A new disease kills them all
4) Can’t compete with another species for food
5) A catastrophic event kills them all
What can random mutations in bacteria lead to?
Changes in bacteria’s characteristics
What can changes in bacteria’s characteristics lead to?
Antibiotic resistant strains
Why can bacteria evolve quite quickly?
Bacteria are so rapid at reproducing
Who are antibiotic strains a problem to?
People who become infected with these bacteria because they aren’t immune to the new strain and there is no effective treatment meaning the infection easily spreads
What happens when the resistant bacteria reproduces more?
The population size of the antibiotic resistant strain increases
What is MRSA?
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
Why is antibiotic resistance getting worse?
The overuse and inappropriate use of antibiotics
3 ways to reduce the rate of development of antibiotic resistant strains
1) Doctors should not prescribe antibiotics inappropriately (non-serious or viral infections)
2) Complete their course of antibiotics so all bacteria are killed and none survive to mutate and form resistant strains
3) The agricultural use of antibiotics should be restricted
Why is it a problem that development of new antibiotics is costly and slow?
We are unlikely to be able to keep up with the demand for new drugs as more antibiotic-resistant strains develop and spread
What is classification?
Organising living organisms into groups
What is the Linnaean system?
A system by Carl Linnaeus which groups living things according to their characteristics and the structures that make them up
What is the order for the Linnaean system?
Kingdom
Phylum
Class
Order
Family
Genus
Species
How are organisms named from the Linnaean system?
According to the Binomial system- first part referring to the genus and the second part referring to the species
What 2 things allowed scientists to put forward new modes of classification?
1) Knowledge of the biochemical processes
2) Microscopes improving
What did Carl Woese propose in 1990?
The three-domain system
What are the 3 large groups in the Three-Domain system?
Archaea (primitive bacteria usually living in extreme environments)
Bacteria (true bacteria)
Eukaryota (includes protists, fungi, plants and animals)
What do evolutionary trees show?
A method used by scientists to show how they believe organisms are related. They use current classification data for living organisms and fossil data for extinct organisms.
