2.4 Variation and Evolution Flashcards
Continuous variation
continuous range with no categories e.g. height
Discontinuous variation
there are distinct groups
heritable variation
caused by having different sets of genes as characteristics are controlled by genes
variation definition
difference in characteristics between individuals of a species or between species
environmental variation
caused by influence of the environment
sexual reproduction
egg fuses with sper (fertilisation)
mothers genes are mixed with fathers
this gives rise to variation
asexual variation
one individual produces offspring that are genetically identical to it - clones
mutation definition
a change in the structure of a gene
how is rate of mutation increased
ionising radiation / some chemicals
gene therapy defintion
techniques used to remove the effects if a harmful allele
by introducing a healthy dominant allele or ‘switching off’ a harmful one.
Putting copies of the normal allele into the cells of a person who has the disorder
Properties of mutations
these changes occur naturally, randomly and often
most have no effect, but some can be beneficial or harmful
What is a “carrier” of a genetic disease
Heterozygous for the recessive trait - Cc - carry the faulty allele but appear healthy
Problems and ethical issues with gene therapy
problems
- the alleles may not go into every target cell
- the alleles may join with the chromosomes in random places, so they do not work properly
- treated cells may be replaced naturally by the patient’s own untreated cells (not permanent cure)
ethical issues
- research is expensive
- some religious groups believe we shouldn’t alter genetics
Why are mutations important
Without them organisms would never change
Why is heritable variation important
Without it, species could never become adapted to their environment
Limitations of modelling natural selection
- model prey does not move
- with card - background is flat not textured
Explaining natural selection - 1- Overproduction - explanation
Most animals and plants have more offspring that can survive - offspring are in a “battle for survival”
Explaining natural selection - 2- Variation - explanation
The offspring are not all the same - they show variation
Explaining natural selection -3 - survival of the fittest to breed - explanation
Some varieties are better equipped for survival than others - these are more likely to survive to breed
Explaining natural selection - 4- breeding - explanation
Those that survive will breed and pass on their heritable characteristics to the next generation (more in this generation will have these characteristics)
Explaining natural selection - 5- species evolved - explanation
Over generations the best characteristics have become more common and will eventually spread to all (majority) individuals
3 reasons extinction can happen
1- the organism as failed to adapt to its environment (virtually unknown)
2 - The organism has adapted to its environment to some extent, but another similar organism has adapted better. The less successful organism cannot compete and will eventually die out.
3 - The organism has adapted to its environment successfully, but the environment suddenly changes and the organism cannot survive or adapt to the new conditions
Antibiotic resistance steps
1- A few bacteria are resistant to the antibiotic
2- Antibiotic is applied
3- Most susceptible bacteria are killed
4-bacteria multiply (increasing resistant numbers)
5- Antibiotic applied again
6- The few remaining susceptible bacteria are killed and the resistant bacteria multiply
7- Antibiotic is now ineffective against resistant bacteria
Examples of natural selection happening over a shorter time period (evidence that evolution is ongoing)
Antibiotic resistance in bacteria
Pesticide resistance
Warfarin resistance in rats
