Variation and evolution Flashcards
what is variation
all the differences in the characteristics of individuals in a population
what are the three causes of variation
- the alleles that individuals have inherited (genetic factors)
- environmental factors
- a combination of both
examples of genetic variation
hair colour
eye colour
examples of environmental variation
- colour of flowers, these depend on the pH of the soil
- language
what causes genetic variation
mutations
what are mutations
random changes to DNA
why dont most mutations change an organisms phenotype
because most of them don’t have an affect on proteins
why would beneficial mutations help organisms
- they may make them more likely to reproduce and pass on their genes to the next generation
- they may be more likely to survive
What theory did Charles Darwin invent
‘Survival of the fittest’
Summarise ‘survival of the fittest’ theory
- traits were being passed on from parent to child
- useful traits were passed on the most
summarise natural selection
the fittest individuals being selected to survive
what did the theory of evolution by natural selection state
states that all species of living things have evolved from simples life forms that first developed more than 3 billion years ago
what is evolution
a change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of new species
why might two populations of one specie not be able to reproduce
because they may have become so different in phenotype that they are unable to interbreed and produce fertile offspring
why are domestic dogs selectively bred
- to be more gentle
why have food crops been selectively bred
to be resistant to disease
why have cows been selectively bred
to produce more meat or milk
why have plants been selectively bred
to have larger or unusual flowers
how is selective breeding carried out - Large cows for meat)
- Take a mixed population of cows and select the largest male and female
- Breed these together
- Since sexual reproduction produces variation in the offspring, the offspring will consist of larger and smaller animals
- Select the largest male and female from the offspring and breed them together
- Continue doing this over many generations until all the offspring are large
what are problems with selective breeding
- if we breed closely related animals or plants, we can get inbreeding, and these may make some breeds prone to health problems or inherited defects (this is because the gene pool is reduced)
- if a new disease appears, since there’s not much variation, all of the species may die out
what is genetic engineering
when genes from one organisms genome are cut out and transferred to cells of a different organism
examples of things that use genetic engineering
- Bacteria have been genetically modified to produce insulin that can be used to treat type 1 diabetes
- GM crops are modified to improve the size or quality of their fruit, or make them resistant to disease, also increase yield
- Sheep have been genetically engineered to produce substances in their milk that can be used to treat human diseases
disadvantages of genetic engineering
- some people say growing GM crops will affect the number of wild flowers that live in and around the crop, reducing farmland biodiversity
- people are concerned about the effects of eating GM crops on human health
- transplanted genes may get into the natural environment, eg a herbicide resistant gene may be picked up be weeds
advantages of genetic engineering
- GM crops increase yield, making more food
- GM crops could be engineered to contain nutrients that are missing from people’s diets
what is gene therapy
using genetic modification to treat inherited disorders in humans
Steps of genetic engineering
- Identify the gene you want to transfer
- Use enzymes to isolate this gene
- Transfer the gene into a small circle of DNA called a plasmid (a vector)
- Finally, the desired gene is transferred into the cells of the target organism (animal, plant, microorganism)
what can we use instead of a plasmid in genetic engineering
a virus
why do we always transfer the gene at an early stage in the organisms development
to make sure all of the cells receive the transferred gene, so the organism develops all the characteristics we want
advantages of cloning plants
- we know exactly what the clone’s characteristics will be as it is genetically identical to the original plant
how to clone plants using cuttings
- A small piece of the plant is removed and dipped in rooting powder
- Plant the cutting to produce clones of the parent plant
why do we use rooting powder when cloning plants
rooting powder contains plant hormones, and this encourages the plant to develop roots
how to clone plants using tissue culture
- Take the plant you want to clone
- Divide the plant into hundreds of tiny pieces
- Each of these pieces contains a small number of cells
- these small groups of cells are then incubated with plant hormones
why are cells incubated with plant hormones when cloning with tissue culture
because the plant hormones stimulate the plant to grow and develop into fully grown clones
why must the conditions we use for tissue culture be sterile
because we dont want to introduce any microorganisms such as bacteria or fungi
why is tissue culture useful
allows growers to produce thousands of genetically identical plants quickly and cheaply
- they can preserve rare species of plant
- because all the plants are clones, gardeners can be certain that they’ll get the characteristics they want, eg flower colour
how to clone mammals step by step (Horses) with embryo cloning method
- Start with a sperm and egg cell from horses with the characteristics we want, these are used to artificially fertilise an egg
- Allow the fertilised egg to develop into an early stage embryo (NOT SPECIALISED)
- Use a glass rod to split this embryo into two
- Transplant the two embryos into host mothers, where the embryo will grow and develop
- When the animals are born, we will get two identical offspring
problems with embryo transplants
- because we start with a sperm and an egg, we cannot be certain that the offspring will have the characteristics that we want
steps of adult cell cloning
- Start by removing a cell from the animal we want to clone
- Remove the nucleus from this cell, as it contains the genetic info from the animal we are cloning
- Take an unfertilised egg cell from the same species
- Remove the nucleus from the unfertilised egg cell so it has no genetic material
5.insert the nucleus from the original adult body cell into the empty egg cell, so that the egg cell only contains genetic info from the animal we are cloning - Electric shock the egg cell
- when the embryo has developed into a ball of cells, it is inserted into the womb of an adult female
what advantage does adult cell cloning have over embryo cloning
- we are cloning from an adult so that means we know what characteristics the clone will have
why do we electric shock the egg cell in adult cell cloning
to make the cell divide to form an embryo
why does the clone look nothing like the host mother in cloning
because the clone contains none of her genetic material
what are some issues with cloning
- reduced gene pool, if a population ate closely related and a new disease appears, they can all be wiped out
- clones may not be as healthy as normal ones
- some people worry that humans may be cloned in the future
advantages if cloning
- could lead to greater understanding of the development of an embryo, and of ageing and age related disorders
- cloning could hep preserve endangered species
what were the three conclusions that Darwin came up with
- individual organisms within a particular species show a wide range of variation for a characteristic
- individuals with characteristics most suited to the environment are more likely to survive to breed successfully
- the characteristics that have enabled these individuals to survive are then passed onto the next generation
what book did Darwin publish in 1859
On the Origin of species
Why was Darwins theory extremely controversial and only gradually accepted
- at the time, a lot of people strongly believed that God made all the animals and plants that lived on Earth and Darwins theory challenged this idea
- at the time, scientists felt that Darwin did not have enough evidence to back up his theory
- people did not understand how characteristics were inherited, genetics were not understood until 50 years after Darwins theory was published
what was Lamarck’s theory
that when a characteristic is regularly used, it becomes more developed, and this strengthened characteristic is then passed onto the offspring
problems with Lamarck’s theory
changes that occur during an organisms lifetime, cannot be passed onto offspring
What did Alfred Russel Wallace work on
- gathering evidence for the theory of evolution independently
- working on warning colours in animals
- the theory of speciation
what is speciation
the development of a new species
when does speciation occur
when populations of the same species become so different that they can no longer successfully interbreed to produce fertile offspring
how do new species form (snails)
- On an island, there are one species of snails which can interbreed, so any beneficial mutation spreads through the whole population
- A geographical barrier such as a river, then separates/isolates the population of snails into 2 groups
- Because the two populations are now separate, theres no interbreeding between the two groups of snails
- Over time, natural selection will favour different alleles on the two sides of the island (eg - the food sources on one side might be different to the other)
- Because there is no interbreeding, any mutations that occur cannot spread between the two populations, meaning over many generations, the two populations of snails will begin to change
what happens if the geographical barrier is removed and species are able to mix
(using snails as example)
- the phenotypes are so different so the two species of snails cannot reproduce to make fertile offspring, now the snails are two different species
what needs to happen in order for speciation to take place
we need a geographical barrier to separate the population into two, and prevent interbreeding between the two populations
what did Gregor Mendel do
- he looked at lots of characteristics in pea plants like the shape of the pod
what conclusions did Mendel come to from his experiments
- characteristics are not blended during inheritance - eg the shape of a pea pod has no effect on the colour of the flower
- Mendel said that characteristics in a plant are determined by hereditary units and these units dont change when passed onto descendants
(we call these units genes) - some characteristics can be masked, then can reappear in later generations (recessive alleles)
why wasnt Mendel accepted
- many scientists still held onto the idea that characteristics are blended when they are inherited
- they did not understand Mendel major discovery, so soon his work was forgotten
Why was Mendels discovery accepted by the early 1900s
- In the late 1800s, behaviour of chromosomes during cell division was observed
- in the 1900s, they realised that Mendel’s units acted in a similar way to chromosomes, by this time his units were called genes, and scientists realised that genes were located on chromosomes
- ## in the mid 1900s, scientists determined the structure of DNA and how genes function
what are fossils
the remains of organisms from millions of years ago which are found in rocks
what are the three ways fossils can form
- from parts of organisms that have not decayed because one or more of the conditions needed for decay are absent
—— eg if its too cold, if theres not enough oxygen or water - when parts of the organisms are replaced by minerals as they decay
- fossils can be the preserved traces of organisms, eg animals can leave footprints or burrows, plants can leave preserved spaces where roots were
problems with fossils
- many of the earliest forms of life were soft bodied organisms, which didnt have a shell or skeleton
- soft bodied organisms rarely form fossils, and many of the fossils that did form had been destroyed by changes to rocks in the Earth’s crust
why are scientists not certain about how life began
because there are very few fossils of the early forms of life
what does it mean when a species is extinct
when no individuals of a species remain
why might species become extinct
- a catastrophic event like an asteroid colliding with the Earth
- a change in environment
- a new disease or predator
- if they cannot compete with another species for food and water
under ideal conditions, how quickly can bacteria reproduce
every thirty minutes
what do antibiotics do
they kill bacteria
- used in farming to prevent animals from developing bacterial diseases
how do bacterial pathogens become resistant to antibiotics
- Mutations of bacterial pathogens produce new strains
- Some strains may be resistant to antibiotics so are not killed
- These survive and reproduce without any competition from other bacteria, so the population of the resistant strain rises
- The resistant strain will then spread as people are not immune to it and there is no effective treatment
three ways we can reduce the development of antibiotic resistant strains of bacteria
- Doctors should not prescribe antibiotics inappropriately, for example to treat viral infections
- Patients should complete their course of antibiotics so that all bacteria are killed and so that none survive to mutate and form resistant strains
- Restrict the use of antibiotics in farming
what is MRSA
a superbug that is resistant to antibiotics
what are problems with developing new antibiotics
it takes a long time and is very expensive, and since antibiotic resistant bacteria emerge all the time, it’s unlikely that we will be able to keep up
what did Carl Linnaeus do
in 1700s, he began to classify species into different categories based on their structure and characteristics
what kingdoms did Linnaeus divide living organisms into
the animal kingdom and the plant kingdom
what were all the categories Linnaeus discovered (in order)
- Kingdom - King
- Phylum - Phillip
- Class - Came
- Order - Over
- Family - for
- Genus - good
- Species - soup
how is every organism named
from their genus and their species (the binomial system)
why were new models of classification proposed
- due to improvements in microscopes
- due to a progression in the understanding of biochemical processes
who discovered the ‘three domain system’
Carl Woese
What are the groups in the three domain system
Archaea - primitive bacteria, found in extreme conditions like hot springs and salt lakes
true bacteria - the kind that live in the human digestive system
eukaryota - animals, plants, fungi, amoeba
what are evolutionary trees used to show
how closely related organisms are to each other
how do scientists make an evolutionary tree
- by using classification data on living organisms like their DNA
- by using fossils for extinct organisms
what does a plasmid do
transfers the DNA from one organism to another
when would we use cuttings to make clones
when we just want a few clones from a plant
when would we use tissue culture
if we want to make hundreds of clones
why might using fossils as classification data, be a problem
the fossil records of many species are incomplete
