Variation and Evolution (bio paper 2

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38 Terms

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What is variation?

All the differences in the characteristics of individuals in a population.

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What are the 3 main causes of variation?

  • The alleles that individuals have inherited (genetic factor)

    • e.g. eye colour and natural hair colour

  • Environment

    • e.g. language in humans

  • Combination of both genes and environment

    • e.g. height

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What is genetic variation due to?

Mutations

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What are mutations?

  • Random changes to DNA.

  • Mutations happen all the time.

  • Most mutations have no effect at all on the phenotype.

  • Some mutations influence the phenotype e.g. tallness

  • Small number of mutations determine phenotype e.g. eye colour

  • Very rarely, mutations can lead to a new phenotype e.g. wild rabbits resistant to virus.

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What is evolution

The change in the inherited characteristics of a population over time through a process of natural selection.

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How many different species of animals and plants are there on Earth?

  • Nearly 9 million

  • This doesn’t include microbes such as bacteria

  • It’s also thought that all these species are only 1% of the total that have ever lived on Earth- rest are extinct.

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When do scientists believe that life first developed on Earth?

More than 3 billion years ago.

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First life forms (from over 3 bill years ago)

  • Very simple e.g. single cells

  • All species of living things have evolved from these simple life forms.

    • This process is called evolution by natural selection.

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Describe evolution of species e.g. rabbits

  • Every rabbit will have a slightly different combination of alleles that it inherited from it’s parents.

  • These alleles can be advantageous depending on the conditions in the environment.

  • E.g. if it’s cold, the rabbits with the alleles for thicker fur have advantageous alleles so they’re more likely to survive and go on to reproduce.

  • Their offspring could inherit the advantageous alleles and be more likely to survive and go on to reproduce.

  • This process is called natural selection.

  • Over many generations, the alleles for thicker fur will become more common among the population of rabbits.

  • Overall the rabbit population will have thicker fur than before.

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What is a species?

  • A group of similar organisms that can reproduce to give fertile offspring.

  • When 2 populations of one species become so different in phenotype they can’t go on to reproduce fertile offspring so they have now become 2 separate species.

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What is selective breeding/artificial selection ?

When humans artificially select the plants or animals that are going to breed, so that the genes for particular characteristics remain in the population.

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4 examples of selective breeding.

  • Domestic dogs have been selectively bred to have a gentle nature.

  • Food crops such as wheat have been selectively bred to be resistant to disease.

  • Animals such as cows have been selectively bred to produce more meat or milk.

  • Certain plants have been selectively bred to produce large or unusual flowers.

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Describe selective breeding e.g. if you want cows with lots of meat

  1. Take a mixed population of cows and select the largest male and female.

  2. Then breed these together.

  3. Select the largest male and female offspring and breed these together.

  4. Continue doing this over many generations until all of the offspring are large.

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Issue of selective breeding

  • If closely related animals or plants are bred together then there may be inbreeding which can cause some breeds to be prone to disease or inherited defects.

  • e.g. dogs have been selectively bred for hundreds of generations and now many dog breeds develop inherited disorders such as joint problems, heart disease or epilepsy.

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What happens during genetic engineering?

  • Genes from one organism are cut out and transferred to cells of a different organism e.g. bacteria

  • OR COULD SAY

  • The genome of the bacteria is modified and now includes a human gene.

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What can genetic engineering be used for?

  • To treat Type 1 diabetes

  • To produce GM crops

  • Gene therapy- long term effects are unknown

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GM crops

  • Generally produce a greater yield than normal crops.

  • GM crops can be made resistant to disease or insect attack.

  • Some produce bigger or better fruits.

  • Some are resistant to herbicides so farmers can spray their field to kill weeds without harming GM crops.

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Disadvantages of GM crops

  • Some question if it’s safe

  • Some people feel that we need to do more research on the health effects of eating GM crops.

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Genetic engineering

  1. Identify the gene that we want to transfer.

  2. Use enzymes to isolate this gene.

  3. Transfer the gene into vector such as plasmid or virus.

  4. Transfer the desired gene in the cells of the target organism.

    • Make sure the transferring of the gene is done at an early stage of an organisms development to ensure that all of the cells receive the transferred gene so the organism develops with the characteristic that we want.

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How do new species form?

  1. Species are separated into 2 populations e.g. by a river.

  2. Natural selection will favour different alleles in the 2 populations.

  3. The 2 groups can’t interbreed so beneficial mutations don’t spread through the 2 groups.

  4. This means that over many generations, the 2 populations of snails will begin to change.

  5. When this barrier is removed the snails can now mix but the phenotypes of the 2 groups are so different that they can no longer reproduce to make fertile offspring, meaning that they’re now 2 different species.

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Gregor Mendel (mid 1800s)

  • Mendel carried out thousands of breeding experiments on pea plants.

  • People didn’t know how inheritance worked and many believed characteristics were blended when inherited.

  • Mendel looked at different characteristics in pea plants and found that characteristics aren’t blended during inheritance.

  • Said characteristics are determined by inherited units which don’t change when passed on to descendants (genes).

  • Also shows that some characteristics can be masked and then appear in later generations (recessive alleles).

  • People ignored and forgot Mendel’s work but it was rediscovered.

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After Mendel’s death

  • In the late 19th century behaviour of chromosomes during cell division was observed.

  • In the early 20th century it was observed that chromosomes and Mendel’s ‘units’ behaved in similar ways.

  • This led to the idea that the ‘units’, now called genes, were located on chromosomes.

  • In the mid-20th century the structure of DNA was determined and the mechanism of gene function worked out.

  • This scientific work by many scientists led to the gene theory being developed.

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What are fossils?

The remains of organisms from millions of years ago which are found in rocks.

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How can fossils form

  • When parts of an organism have not decayed.

    • conditions needed for decay are absent.

  • Parts of the organism are slowly replaced by minerals during the decay process.

  • Preserved traces e.g. footprints

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Issues with fossils

  • Many of the earliest forms of life were soft-bodied organisms.

  • These rarely form fossils so not many traces left behind.

  • Whatever traces were left behind were destroyed by geological activity

  • This is why scientists cannot be certain about how life began on Earth.

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What can fossils show?

  • That a huge number of species have become extinct.

  • How much or how little different organisms have changed as life developed on Earth.

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Why do species become extinct?

  • Catastrophic event e.g. asteroid

  • Environment changes (can also be caused by catastrophic event).

  • New disease

  • New predator

  • Competition

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Which type of organism evolves extremely rapidly?

  • Bacteria

  • This is because they can reproduced quickly (30 mins in ideal conditions).

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Uses of antibiotics

  • Medicine

  • Farming (to prevent animals from developing bacterial diseases.)

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Antibiotic- resistant bacteria (e.g. MRSA)

  1. Mutation could make a bacterium resistant to antibiotics.

  2. Bacterium not killed so survives and reproduces.

  3. Resistant strain rises and spreads because people aren’t immune to it.

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3 ways to prevent antibiotic resistant strains

  • People shouldn’t overuse antibiotics.

  • Not take it for unnecessary things such as a virus.

  • Patients should complete their full course of antibiotics as this ensures all the bacteria are killed so none can survive to mutate and form resistant strains.

  • Restrict the use of antibiotics in farming.

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Issue with researchers currently developing new antibiotics.

  • Expensive.

  • Slow process- unlikely to keep up as new resistant strains emerge all the time.

  • Takes a long time.

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Carl Linnaeus

  • Classified species into different categories based on their structure and characteristics.

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Linneaus’s system

  • Divided all living organisms into 2 kingdoms- plant and animal.

  • Divided each kingdom into smaller categories.

  • Memorise this with mnemonic: King Phillip came over for good soup.

  • Based on characteristics that can be seen.

  • As evidence of internal structures became more developed due to improvements in microscopes, and the understanding of biochemical processes progressed, new models of classification were proposed -3 domain system

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Classification mnemonic

Kingdom

Phylum

Class

Order

Family

Genus

Species

King Philip came over for good soups

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What’s the binomial name?

  • Genus then species

  • The binomial system is used worldwide and means that scientists across the world all refer to a particular species by the same name.

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3 domain system

  • Developed by Carl Woose

  • Archae- primitive bacteria often found in extreme environments e.g. hot springs

  • True bacteria- Live in human digestive system.

  • Eukaryota- (animals, plants, fungi, protists).

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What is an evolutionary tree used for?

  • To show how closely related organisms are to each other.

  • To make an evolutionary tree, scientists can use classification data on living organisms e.g. their DNA.

  • However for extinct organisms, scientists have to use fossils which is an issue because fossils records of many species are incomplete.