Evolution and Natural Selection Flashcards Preview

Z Biology GCSE > Evolution and Natural Selection > Flashcards

Flashcards in Evolution and Natural Selection Deck (21)
Loading flashcards...
1
Q

What can variation in a species be?

A

Genetic, environmental, or a combination of both

2
Q

Describe variation

A
  1. Most variation in animals is caused by a mixture of genetic and environmental factors
  2. Almost every single aspect of a human (or other animal) is affected by our environment is some way, however small
3
Q

What are some examples of variation not due to environmental factors?

A
  1. Eye colour e.g. genotype for blue eyes, your eyes will be blue, if you have genes increasing you levels of HGH you will grow taller than you otherwise would
  2. Hair colour (in most animals, not if someone dyes their hair)
  3. Inherited disorders e.g. haemophilia and cystic fibrosis
  4. Blood group
4
Q

What are some examples of variation that are affected by environmental factors?

A
  1. Environment can have a large affect on human growth even before some is born, for example a baby’s weight at brith can be affected by the mother’s diet
  2. And having a poor diet, whilst you are growing can stunt your growth, another environmental variation
  3. E.G. limited protein supply in your habitat you will grow quite short
  4. If you live somewhere with high levels of sunshine you skin will tan
5
Q

What are some examples of variation which are affected by both genetic and environmental factors?

A
  1. Health: some people are more likely to get certain diseases (e.g. cancer and heart diseases) because of their genes. But lifestyle also affects the risk, e.g. if you smoke or only eat junk food
  2. Intelligence: one theory is that although your maximum IQ might be determined by your genes, whether you get to it depends on your environment e.g. upbringing and school life
  3. Sporting ability: again genes probably determine your potential, but training is important too
6
Q

Why is environmental variation in plants much greater?

A
  1. Plants are strongly affected by, light moisture level, temperature and the mineral content of the soil
  2. For example plants might grow twice as big or twice as fast due to fairly modest changes in environment such as the amount of sunlight or rainfall they are getting, or how warm it is or what the soil is like
    - If you give your pot plant some plant food, full of minerals, then you plants grows loads faster
    - Farmers and gardeners use mineral fertilisers to improve crop yield
7
Q

What does adaptation mean?

A

Making changes to survive and suit the environment

8
Q

What is the theory of evolution?

A
  • Life began as simple organisms from which more complex organisms evolved, rather than just appearing into existence
  • The whole process of evolution usually takes place gradually over millions of years
9
Q

What does natural selection mean?

A
  • “survival of the fittest’ (explanation of how natural selection works)
    1. Living things show variation and there are not all the same
    2. The resources living things needed to survive are limited. Individuals must compete for these resources to survive, only some of the individuals will survive
    3. Some of the varieties of a particular species will have a better chance of survival
    4. Those varieties will then have an increased chance of breeding and passing on their genes
    5. This means that a greater proportion of individuals in the next generation will have the better alleles, and so the characteristics, that help survival
    6. Over many generations, the species becomes better and better able to survive
    7. The ‘best’ features are naturally selected and the species becomes more and more adapted to its environment
10
Q

What is an example of natural selection

A
  1. Bunnies with short ears, then big ear bunny, better as hear more and so get away from predator faster. Eventually only big eared rabbits left because the rest died as did not hear trouble quick enough :(
  2. This is how populations adapt to survive better in their environment (an organism does not actually change when it is alive, changes only occur from generation to generation
  3. Over many generations the characteristic that increases survival becomes more common in the population. If member of a species are separated somehow, and evolve in different ways to adapt to different conditions, then over tome you can end up with two totally different species
  4. Another example is dark form of peppered moth was then better in industrial UK as then hide in soot as tree covered with soot
11
Q

Why do the best genes for a particular environment tend to survive?

A
  1. The individuals who are less suited to an environment are less likely to survive than those that are better suited, and so have less chance of passing their alleles on. Gradually, over time, this results in a population which is extremely well suited to the environment in which it lives
  2. REMEMBER: Variations that are caused by the environment itself (e.g. accidentally losing a finger) are not involved in natural selection. Variations in species can have either environmental or genetic causes, but only the genetic ones are passed on to the next generation and influence the evolution of the species
12
Q

What is a mutation?

A
  1. A mutation is a rare, random change in genetic material that can be inherited
  2. Mutations change the sequence of the DNA bases. This could stop the production of a protein, or it might means a different protein is produced instead
  3. This can lead to new characteristics increasing variation
  4. A mutation must happen in the gamete rather than in a somatic cell for it to be passed on to offspring
13
Q

What are mutations usually?

A
  • Harmful
    1. If a mutation occurs in reproductive cells, the offspring might develop abnormally or die
    2. If a mutation occurs in body cells, the mutant cells might start to multiply in an uncontrolled way and invade other parts of the body (which is cancer)
14
Q

What are mutations when they are not harmful?

A
  1. Some mutations have no effect at all, for example, if they occur in an unimportant part of the DNA, these mutations are said to be NEUTRAL
  2. Very occasionally mutations are BENEFICIAL and give and organism a survival advantage, so it can live in condition where the others die. This is natural selection at work
    - E.G. A mutation in a bacterium might make it resistant to antibiotics. If this mutant gene is passed on, you might get a resistant “strain” of bacteria, which antibiotics can’t kill
15
Q

Describe how bacteria can evolve and become antibiotic resistant?

A
  1. Like all organisms, bacteria sometimes develop random mutations in their DNA
  2. These can lead to changes in the bacteria’s characteristics
  3. Sometimes, they mean that a bacterium is less affected by a particular antibiotic
  4. For the bacterium, this ability to resist antibiotics s a big advantage. It is better able to survive, even in a host who is being treated to get rid of the infection, and so it lives for longer and reproduces many more time
  5. This leads to the gene for resistance being passed on to lots of offspring, it is just natural selection. This is how it spreads and becomes more common in a population of bacteria over time
    - Therefore resistance to antibiotics can increase in bacterial populations
    - Organisms can become resistant to pesticides and other chemicals in the same way
16
Q

Why is antibiotic resistance bad for people who become infected?

A
  1. This is a problem for people who become infected with these bacteria, because you can’t easily get rid of them with antibiotics
  2. Sometimes drug companies can come up with a new antibiotic that is effective, but ‘superbugs’ that are resistant to most known antibiotics (e.g. MRSA) are becoming more common
17
Q

How can antibiotic resistance be helped?

A
  1. If you are prescribed antibiotics, it is important to finish the whole course, this helps to prevent the spread of antibiotic resistance
  2. Doctors only prescribing antibiotics when they are really needed helps too
18
Q

Why do mutations happen?

A
  • Mutations can happen spontaneously, when a chromosome does not quite copy itself properly
  • However, the chance of mutation is increased by exposing yourself to:
    1. Ionising radiation, e.g. X-rays, gamma rays or ultraviolet light
    2. Chemicals called mutagen e.g. chemicals in tobacco
  • If the mutations can lead to cancer then the chemicals are called carcinogens
19
Q

What is genetic variation caused by?

A
  1. Sexual reproduction

2. Mutations in genes

20
Q

Describe the stages of natural selection

A
  1. There is variation in a population
  2. Conditions in a changing environment (a selection pressure) favours certain forms with certain adaptations (a selective advantage)
  3. The frequency of the favoured form increase (survival of the fittest)
  4. The frequency of the rest decreases, they are selected against
  5. The population looks more like those with the advantageous adaptation
21
Q

Why do antibiotic evolve very quickly?

A
  1. Very short generation time (a little as 20mins)
  2. Limited/no mutation checking
  3. Transfer of plasmids