Variation and evolution Flashcards
The development of understanding of genetics and evolution
Our current understanding of genetics has…
… developed over time.
Describe the development of our understanding of genetics (aka the history run-down) - Late 1800s
Late 1800s - scientists discovered chromosomes and observed how they behaved during cell division
In the early 1900s, scientists discovered similarities in the way that chromosomes and Mendel’s ‘hereditary units’ acted.
What was proposed as a result?
That the ‘hereditary units’ (now known as genes) are located on chromosomes.
Who was Gregor Mendel?
Mendel was an Austrian scientist and monk who lived in the 1800s.
He is referred to as the ‘founding father of modern genetics’.
Briefly describe the work of Mendel
Mendel carried out breeding experiments on plants in the mid 1800s/19th Century.
One of his observations was that the inheritance of each characteristic is determined by ‘units’ that are passed on to descendants, unchanged.
Describe the development of our understanding of genetics (aka the history run-down) - Early 1900s
Early 1900s - scientists discovered similarities in the way that chromosomes and Mendel’s ‘hereditary units’ behaved.
Describe the development of our understanding of genetics (aka the history run-down) - 1953
1953 - The structure of DNA (e.g. double helix) was determined and the mechanism of gene function worked out.
This scientific work led to the gene theory being developed.
Which three traits of the pea plant (the species he used) did Mendel study?
Colour of peas
Colour of flowers
Height
What did Mendel study?
The inheritance of different characteristics: He devised the laws of inheritance!
What was the pattern in characteristics found by Mendel?
First cross- all offspring had the dominant ‘hereditary unit’ (Tt for height)
Second cross - 1/4 had hereditary units that were both recessive. (tt for height).
They expressed a different characteristic to the other pea plants e.g. were dwarfs/green.
What were the three conclusions made by Mendel?
-Characteristics in plants are determined by ‘hereditary units’ (genes)
-Hereditary units are passed on to offspring unchanged, with one unit from each parent
-Hereditary units can only be dominant or recessive - if an individual has both the dominant and recessive unit for a characteristic, then the dominant characteristic will be expressed
Variation
Differences in the characteristics of individuals in a population.
What might cause variation?
-the genes that individuals in a population have inherited (genetic causes)
-the conditions in which the individuals in a population have developed (environmental causes)
-a combination of genes and the environment
What usually exists within a population of a species?
There is usually extensive genetic variation within a population of a species.
What is the effect of a mutation on an individual’s phenotype?
-Most have no effect on the phenotype
-Some influence phenotype
-Very few determine phenotype
What does the variation within a population of a species arise from?
Mutations.
Mutations occur _______.
Continuously
How often will a mutation will lead to a new phenotype?
Very rarely.
However, if there IS a new phenotype, and it’s suited to an environmental change, it can lead to a relatively rapid change in the species.
What are the two types of variation?
-Genetic variation
-Environmental variation
What causes genetic variation?
(linked to how the genome influences the development of the phenotype of an organism).
-The mixing of genetic information
-When gametes fuse
-You inherit some genes from your mother, and some genes from your father
Name some characteristics in animals determined only by genes:
-eye colour
-blood group
-inherited disorders
What is haemophilia?
An inherited disorder where you bleed more than other people.
(not in spec but interesting x)
Genome
All of the genetic material in an organism.
How does the genome’s interaction with the environment influence the development of the phenotype of organisms?
The environment, including all of the conditions that the organisms live and grow in, cause differences between members of the same species.
This is called environmental variation.
e.g. A plant grown in lots of sunlight would be luscious and green vs one grown in darkness which would be tall and spindly with yellow leaves.
A twin may go on holiday and get tanned so look physically different to the other, or gain weight through a diet high in saturated fat.
Give an example of how a combination of genes and the environment affect phenotype.
(its a combo for most things btw x)
Genes could determine the maximum height a plant or animal can grow to, but whether it actually grows that tall depends on the environment (e.g. how much food it gets).
What is the theory of evolution? (by natural selection)
All species of living things have evolved from simple life forms that first developed more than three billion years ago.
Evolution
A change in the inherited characteristics of a population over time, through a process of natural selection, that may result in the formation of new species.
According to Darwin and Wallace’s theory, why do giraffes have long necks?
-There was variation among the giraffe population, due to a random mutation in genes
-So some had longer necks than others
-Those giraffes with longer necks were better adapted to their environment, as they could eat leaves from taller trees.
-So, they had a higher chance of surviving and reproducing
-They passed on their advantageous alleles (coding for long necks) to their offspring.
-Over many generations, the long-neck allele became the most common
-This is an example of evolution by natural selection
Speciation
The phenotype of an organism changing so much (because of natural selection) that a new species is formed.
(the development of a new species)
Which scientist nearly published his findings on speciation before Charles Darwin?
Alfred Russel Wallace
Explain how evolution occurs in one sentence.
Evolution occurs through natural selection of variants that give rise to phenotypes best suited to an environment.
Explain the evolution of […] using the theory of natural selection - top mark structure! x
There is variation among the […] population due to a random mutation in genes
-so some […] and some […] (describe the phenotypes)
-Those […] that are […] are better adapted to their environment because […] so are more likely to survive
-They are therefore more likely to reproduce and pass on their advantageous alleles
-Over many generations, the […] allele became the most common
-This is an example of evolution by natural selection
Explain the evolution of […] using the theory of natural selection - what must we mention when answering?
1.variation
2.adaptation
3.competition
4.survival and reproduction
5.evolution by natural selection
Who proposed the theory of evolution by natural selection?
Charles Darwin
(&Alfred Russel Wallace)
What did Charles Darwin use to propose the theory of evolution by natural selection?
-The observations from his round-the world expedition
-Years of experimentation and discussion
-Developing knowledge of geology and fossils
Outline Darwin’s theory of evolution by natural selection
-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 and breed successfully
-The characteristics which enabled these individuals to survive are then passed on to the next generation
Why are individuals with characteristics most suited to the environment more likely to survive and breed successfully?
Organisms have to compete for limited resources in an ecosystem.
Organisms with characteristics most suited to the environment are more successful competitors, so more likely to survive.
This is known as ‘survival of the fittest’.
What causes new phenotypic variations to arise?
Genetic variants produced by mutations (changes in the base sequence of DNA).
How are beneficial variations passed to offspring?
In genes. (during the fusion of gametes).
Where did Darwin publish his ideas?
A book called ‘On the Origin of Species’ (1859).
Why was the theory of evolution by natural selection only gradually accepted?
Darwin’s ideas were controversial as…
-The theory challenged the idea that God made all the animals and plants that live on Earth
-There was insufficient evidence at the time the theory was published to convince many scientists
-The mechanism of inheritance and variation was not known until 50 years after the theory was published.
What could Darwin not explain?
The mechanism of inheritance and variation:
-That useful characteristics appeared due to mutations
-That these are passed on from individual organisms to their offspring in genes
Why was there insufficient evidence to convince other scientists of Darwin’s theory of evolution by natural selection?
Few other studies had been conducted into how organisms change over time.
Name the naturalists you need to know about.
-Mendel
-Darwin
-Wallace
-Lamarck
What are theories of evolution other than Darwin’s (e.g. Lamarck’s) mainly based on?
The idea that if a characteristic is used a lot by an organism, it would develop over the organism’s lifetime.
These changes can be inherited by that organism’s offspring.
e.g. a rabbit that used its legs to run a lot, escaping predators, its legs would get longer. The offspring of that rabbit would then be born with longer legs.
According to Jean-Baptise Lamarck, (1744-1829), why do giraffes have long necks?
-They started with short necks
-They stretched their necks to reach higher branches for food, so their necks got longer
-The long neck trait was inherited by their offspring
How do we know inheritance of characteristics acquired by an organism during its lifetime cannot occur?
(e.g. inheritance according to Lamarck)
Modern genetics show that the characteristics acquired by an organism during its lifetime do not affect the DNA sequence of the organism.
They therefore can’t be inherited (passed down from one generation to the next).
Experiments did not support his hypothesis.
The theory of evolution by natural selection developed…
…over time and from information gathered by many scientists.
Describe the work of Darwin and Wallace.
-Charles Darwin and Alfred Russel Wallace independently proposed the theory of evolution by natural selection
-They arrived at a similar conclusion so published joint writings in 1858
-This prompted Darwin to publish ‘On the Origin of Species’ the following year, providing additional support to the theory
Explain the impact of Darwin and Wallace’s ideas (about evolution by natural selection) on biology.
Wallace did much pioneering work on speciation; more evidence over time has lead to our current understanding.
Darwin’s ideas are supported by the discovery of genetics: organisms born with beneficial characteristics pass them to offspring in genes.
His work has influenced various fields, including genetics, ecology, and palaeontology
‘On the Origin of Species’ (1859)
The book suggests that natural selection is the driving force behind the gradual development of species over time.
It became famous and is the reason Darwin is regarded as the one who discovered evolution.
Alfred Russel Wallace
A scientist at the same time as Darwin.
He worked worldwide, gathering evidence for the theory of evolution by natural selection.
He is best known for his work on warning/’aposematic’ colouration in animals, and his theory of SPECIATION.
What are warning/’aposematic’ colours?
Bright/distinctive colours/patterns used by some species (e.g. butterflies) to deter predators from eating them.
Wallace said this was an example of a beneficial characteristic that has evolved through natural selection.
The theory of speciation has…
…developed over time.
Supporting evidence for Darwin’s theory?
-The discovery of genetics
-The fossil record (looking at fossils of different ages)
-Knowledge of how resistance to antibiotics evolves in bacteria
At what point has speciation occurred?
When populations of one species become so different in phenotype that they can no longer interbreed to produce fertile offspring.
(they are ‘reproductively isolated’)
Inbreeding vs interbreeding
Breeding of genetically similar parents
vs
Breeding between two different species the same genus.
Describe the steps that give rise to new species.
-Different populations become geographically isolated (e.g. by a mountain/river)
-There is variation in each population due to a random mutation in genes
-The populations on each side faces different selection pressures
-Natural selection will occur, favouring the alleles that are advantageous in each environment
-Over many generations, the populations become so genetically different that they can no longer interbreed to produce fertile offspring
Species
A group of genetically similar organisms that can interbreed to produce fertile offspring.
What two things lead to speciation?
-Geographical isolation
-Natural selection
What can cause geographical isolation?
A physical barrier (such a new river or mountain range) separating two different populations of a given species
How does geographical isolation lead to speciation?
The environment will be slightly different on either side of a barrier e.g. the climate/food sources = different selection pressures.
What is extinction?
When there are no remaining individuals of a species left alive.
The theory of evolution by natural selection is now…
…widely accepted.
What is now available to support the theory of evolution? (1 word)
Data!
What are fossils?
The ‘remains’ of organisms from millions of years ago, which are found in rocks.
What can we learn from fossils?
How much or little different organisms have changed as life developed on Earth.
You need to be able to read…
…evolutionary/’phylogenetic’ trees
How can fossils form in rocks?
-Preservation
-Gradual replacement by minerals
-From casts and impressions
Formation of fossils - preservation
-Fossils form from parts of organisms that have not decayed because one or more of the conditions needed for decay are absent
-E.g. in amber/tar pits, there is not oxygen or moisture, so decay microbes cannot survive…peat bogs are too acidic for decay microbes…and it is too cold in glaciers for decay microbes to function
Formation of fossils - gradual replacement by minerals (most fossils)
Parts of the organism such as teeth/shells/bones (which don’t decay easily) last a long time when buried.
Eventually, they are replaced by minerals as they decay.
This forms rock-like substances shaped like the original parts.
The surrounding sediment also turns to rock, but the fossil stays distinct & is eventually dug up.
Formation of fossils - from casts and impressions
Fossils are sometimes found as traces of organisms, such as footprints, burrows, and rootlet traces:
-An organism is buried in a soft material like clay
-This later hardens around it
-The organism decays, leaving a cast of itself.
- An animal’s burrow, or plant roots (=’rootlet traces’) can be preserved as casts.
-Footprints may be pressed into a soft material like clay
-This leaves an impression when the material hardens.
What disgusting thing was found in a peat bog? (for fun x)
A fully preserved man they named ‘Pete Marsh’.
Why can scientists not be sure how life on Earth began?
-Many early life forms were soft-bodied, so decayed quickly and left few traces behind
-What traces there may have been have been mainly destroyed by geological activity e.g. the movement of tectonic plates may have crushed fossils in the rock
What are some hypothesis as to how life on Earth began?
-The first living beings coming to existence in a primordial swamp, or under the sea
-Simple organic compounds being brought to Earth on comets, which then evolved into more complex organisms
Name the first antibiotic.
Penicillin
Why can bacteria evolve rapidly?
Becuase they reproduce at a fast rate.
Explain how strains of resistant bacteria can develop.
-A random mutation occurs in the DNA of a bacterial pathogen, producing a new strain.
-If this strain has developed a gene for antibiotic resistance, the bacteria will not be killed
-They survive and reproduce, causing the population of the resistant strain to rise
-They will then spread from person to person
Why do strains of resistant bacteria spread?
Because people are not immune to it and there is no effective treatment.
Why does a gene for antibiotic resistance become more common in a population of bacteria?
Because of natural selection.
How can antibiotic strains of bacteria be treated?
Drug companies developing a new antibiotic. which IS effective.
What is the problem with just developing new antibiotics?
Superbugs (bacteria resistant to most antibiotics) are becoming more common.
Give an example of a superbug.
MRSA.
This superbug is really hard to get rid of.
It often affects people in hospitals, and can be fatal if it enters their bloodstream.
What is MRSA resistant to?
antibiotics
How can we reduce the rate of antibiotic strains of bacteria developing?
-Doctors should not prescribe antibiotics inappropriately (e.g. to treat non-serious or viral infections)
-Patients should complete their full course of antibiotics, so that all bacteria are killed and none survive to mutate and form resistant strains
-Restricting the agricultural use of antibiotics
Why is the problem of antibiotic resistance getting worse?
-Inappropriate use e.g. to treat viral infections
-Overuse in humans
-Overuse in agriculture
Why is using antibiotics more often than needed bad?
It creates more situations where naturally resistant bacteria have an advantage - and can increase in number.
Overuse of antibiotics in agriculture
(concern over this has led some countries to restrict use)
Antibiotics are given to animals to prevent them from becoming ill and to make them grow faster (improved gut health etc.- fix using notes (big book)
This can lead to the development of antibiotic resistant bacteria in the animals, which can then spread to humans e.g. when consuming meat
Why is the development of new antibiotics unlikely to keep up with the emergence of new bacterial strains?
The process is costly and slow.
The development of new antibiotics is unlikely to do what?
Keep up with the emergence of new bacterial strains.
The death rate from infectious bacterial diseases has fallen rapidly in…
…the last few decades…but the problem is getting worse :(
Traditionally, how have living things been classified?
Using a system developed by Carl Linnaeus, which groups living things based on their structure and characteristics.
What is Car Linnaeus’ system for classifying living things called?
The Linnaean System
What is the pneumonic for classification?
(according to the Linnaean system)
King
Philip
Came
Over
For
Good
Soup
What groups does the Linnaean system use to classify living things?
Kingdom
Phylum
Class
Order
Family
Genus
Species
What is the binomial name for humans?
Homo sapiens
How are organisms named?
According to the Binomial system, where every organism is given a two-part Latin name.
How does the Binomial naming system work?
The binomial name is made from the genus and the species:
1st name = genus, 1st letter capitalised
2nd name = species, no capitals
The whole name is in italics/underlined for exams
What does the genus of an organism tell you?
The organisms ancestry.
Why is the Binomial naming system good?
It is a worldwide system, so scientists from around the world can refer to a particular species, using its unique name, despite speaking in different languages.
This avoids confusion.
Who proposed the ‘three domains’ classification system in 1990?
Carl Woese
Describe the impact of developments in biology on classification systems.
-Microscopes improved, allowing us to find out more about the internal structures of organisms
-Knowledge of biochemical processes taking place inside organisms improved as a result
-New chemical analysis techniques such as RNA sequence analysis developed
How did Carl Woese find that some species are not as closely related as thought previously?
(using the Linnaean classification system)
Using evidence gathered from new chemical analysis techniques such as RNA sequence analysis.
(& looking at differences in sub-cellular structures/’organelles’)
What are the three large groups (domains) called?
(three domain system)
-Archaea
-Bacteria
-Eukaryota
Archaea
Primitive bacteria usually living in extreme environments such as salt lakes.
They are a type of prokaryotic cell.
Bacteria, in the three-domains system, are also known as what?
TRUE bacteria
e.g. E-coli.
Eukaryota
Includes protists, fungi, plants, and animals.
What is the difference between archaea and true bacteria?
Their biochemistry.
What are evolutionary trees used for?
They are a method used by scientists to show how they believe different organisms/species are related.
Where do scientists get the data for evolutionary trees from?
Living organisms - current classification data
Extinct organisms - fossil data
What does it mean when a line splits into two on an evolutionary tree?
This shows where a common ancestor split into two different species.
The more recent the common ancestor, the more…
…closely related the two species are, and so the more likely they are to share characteristics.
What is selective breeding also known as?
Artificial selection.
What is selective breeding?
The process by which humans breed plants and animals for particular genetic characteristics.
How long have humans been selectively breeding organisms?
Thousands of years, since they first bred food crops from wild plants, and since they domesticated animals.
Describe the process of selective breeding.
-Choose parents with desired characteristics from a mixed population
-Breed together
-From the offspring, breed those with the desired characteristics together
-Repeat over many generations until all the offspring show the desired characteristic
Which genetic characteristics are selectively bred for?
Ones that are useful or attractive.
For example, animals that produce more meat/milk; food crops with disease resistance; plants with large or unusual flowers; domestic dogs with a gentle nature.
How can selective breeding be used in farming?
To improve crop/meat yields.
e.g. breeding cows and bulls with the best characteristics for producing meat over several generations.
What is the main problem with selective breeding?
Inbreeding reduces the ‘gene pool’.
This means some breeds are particularly prone to disease or inherited defects.
What is the gene pool?
The number of different alleles in a population.
What is inbreeding?
The breeding of organisms closely related/genetically similar (because these tend to have the desired traits).
Give an example of an organism prone to defects due to inbreeding.
The inbreeding of pugs with small noses means many now have breathing problems.
Apart from reducing the gene pool, what is another problem with inbreeding?
It reduces variation, which decreases a population’s chance of survival if a new disease appears.
(as there’s less chance of any resistant alleles being present in the population).
How would plants be selectively bred?
Use the pollen of one to fertilise the other.
Grow offspring and select ones with the highest yield.
What is genetic engineering?
A process which involves modifying the genome of an organism.
This is done by introducing a gene from another organism to give a desired characteristic.
Why have plant crops been genetically engineered?
To be resistant to diseases/chemicals or to produce bigger fruits.
Why have bacterial cells been genetically engineered?
To produce useful substances (such as human insulin to treat type 1 diabetes).
Describe the main steps in the process of genetic engineering.
-Isolate the gene that codes for the desired characteristics and cut out using enzymes
-Insert this gene into a vector (usually a bacterial plasmid or virus)
-Use the vector to insert the gene into the required cells at an early stage of development (e.g. embryo stage)
Describe how GM insulin can be made.
1- isolate the gene that codes for insulin
2- cut the insulin gene out with enzymes
3- extract a plasmid vector from bacteria
4- cut the plasmid with an enzyme
5- insert the insulin gene into the plasmid vector
6- insert the plasmid vector into the bacteria
7- the bacteria reproduce by binary fission: you now have many bacteria that produce human insulin
8- extract and purify the insulin
Where is the embryo of a plant found?
The seeds of its parent.
Why are genes transferred to the cells of animals/plants/microorganisms at an early stage of development?
So the organism develops with the desired characteristic(s).
What is gene therapy?
GM treatments for inherited diseases caused by ‘faulty’ genes.
For example, the insertion of working genes into people with the disease.
What have sheep been genetically engineered to produce?
Drugs in their milk that can be used to treat human diseases.
What are GM crops?
Crops that have had their genes genetically modified. They include crops that are resistant to insect attacks or herbicides, and generally show increased yields.
Explain the potential benefits of genetic engineering in agriculture and medicine.
If plants are engineered to survive in harsh conditions, this can increase food security.
An increased yield can provide a higher profit for farmers.
Modern medical research is exploring the possibility of genetic modification to overcome some inherited disorders.
Explain the potential risks of genetic engineering in agriculture (and medicine).
Eating genetically engineered crops may have unknown negative impacts on human health.
GM crops will outcompete other plants in an area (e.g. wildflowers), which reduces biodiversity.
The gene for e.g. frost resistance may be passed onto wild plant populations and cause resistance in unwanted organisms. e.g. ‘superweeds’ which cannot be killed by herbicides.
How can GM crops help people in developing nations?
Crops can be genetically engineered to contain nutrients missing from peoples’ diets e.g. beta carotene in golden rice to prevent blindness.
Some people have objections to _______ ___________.
genetic engineering - unplanned problems could be passed onto future generations!
but its an exciting new area of science with the potential for solving many of our problems. x
(you get the gist move on)
How can plants be cloned?
-By using tissue culture
-From cuttings
How is tissue culture used to clone plants?
Small groups of cells from part of a plant (side stem) are used to grow new, genetically identical plants.
Why is using tissue culture to clone plants important?
It’s important for preserving rare plant species that are hard to reproduce naturally.
It can be used commercially in plant nurseries to grow many clones of a plant very quickly (for use as stock).
How are cuttings used to clone plants?
This is an older, simpler method used by gardeners to quickly produce many identical new plants from a parent plant.
(Cuttings with buds are kept in moist conditions until they’re ready to plant).
What is an embryo transplant?
Cells from developing animals are split apart before they become specialised.
The identical embryos are transplanted into host mothers.
E.g. from the best bull and best cow to produce hundreds of genetically identical, ‘ideal’ calves.
Describe the process of adult cell cloning (yet another method used to produce a clone)
-The nucleus is removed from an unfertilised egg cell
-The nucleus from an adult body cell (e.g. a skin cell) is inserted into the egg cell
-An electric shock stimulates the egg cell to divide and form an embryo
-The embryo cells contain the same genetic information as the adult body cell
-When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue its development
Which cloning technique was used to create ‘Dolly’ the cloned sheep?
Adult cell cloning.
Explain the potential benefits of cloning in agriculture and medicine.
-Gets you offspring with desired characteristics
-Can be used to preserve endangered species
-The study of animal clones could lead to a greater understanding of the development of embryos, of ageing, and of age-related disorders
Explain the potential risks of cloning in agriculture and medicine.
-A reduced gene pool = less variation = more likely to be wiped out by disease
-Cloned animals may not be as healthy as normal ones (e.g. Dolly the sheep had arthritis, which tends to occur in older sheep)
-Some people worry that humans will be cloned in the future - unsuccessful attempts may lead to children suffering from severe disabilities
