Variation And Natural Selection Flashcards
What is variation?
Differences in the characteristics of individuals in a species
What is continuous variation?
The type of variation categorised by gradual change in a characteristic across a population
What is discontinuous variation?
The type of variation in which all the individuals can be clearly divided into two or more groups and there are no intermediate (in between) states
Give an example of continuous variation
An organism’s height or weight
both are numerical
Give an example of discontinuous variation
An animal’s fur colour / human’s blood type / shoe size / rolling tongues etc.
All can be categorised into distinct groups
How is continuous variation usually represented?
Histograms
How is discontinuous variation usually represented?
Bar charts
What are the 2/3 causes of variation?
- environment
- genetic mutations
(Or both)
What are genetic mutations?
A random change in number of chromosomes or type of gene
Give an example of variation caused by mutations
- genetic disorders like Down syndrome
- blood type
- skin / fur colour at birth
- eye colour
Etc
Give an example of variation caused by environment
- scars
- language
Etc.
How does meiosis cause variation?
How is this increased by reproduction?
- chromosome arrangements are mixed up during meiosis - independent assortment
- When gametes fuse, they will have unique genes (two different zygotes)
Give an example of variation caused by environment and genetics
- weight
- height
- skin colour
- hair colour
Etc.
How often do mutations occur?
Are they visible?
- Continuously
- not always, don’t change phenotype usually
What is meant by an adaptive phenotype?
a phenotype suited to environmental change
What are genetic variants?
Changes in DNA as a result of mutation
Explain Darwin’s ’survival of the fittest’ principal
Individuals with genes and characteristics most suited to the environment are more likely to survive and breed successfully
Why do are characteristics inherited (natural selection)?
The genes and characteristics that have enabled the species to survive are then passed on
Explain natural selection (2)
- A process where individuals in a population display variations that put them at a biological advantage,
- increasing the chances that these individuals will successfully reproduce and pass on their adaptive traits
What is evolution (3)
- A change in the inherited characteristics of a population over a long period of time
- due to changes in environment
- through the process of natural selection, can result in speciation
What is speciation
An outcome of evolution and isolation, where two populations of a species become so distinct they can no longer interbreed to produce fertile offspring
What is a modern day example of natural selection
Antibiotic resistance in bacteria
How does extinction occur?
When natural selection is too slow for organisms to adapt to new conditions
What are fossils?
The remains of organisms from millions of years ago that are found in rocks, peat, ice or amber
How are fossils formed?
From parts of organisms that have not decayed, when parts of organisms are replaced by minerals, as trace fossils
What is decay?
The breakdown of dead organic matter by microbes (such as bacteria) and detritivores e.g. worms
decay may not occur if there aren’t these conditions
Give examples of trace fossils?
Footprints, burrows, shell impressions, rootlet traces that are preserved as fossils
What are the issues with the fossil record
Not all organisms fossilise and many early forms of life were soft-bodied, so very few traces of these organisms have been left behind
Why is there difficulty in determining the origin of life
Geological activity has destroyed most traces of early life forms
Why is interpreting the fossil record useful?
We can learn how much or how little
organisms have changed as life developed on Earth
what do fossils prove? (2)
- That fossils are very similar to existing organisms
- suggesting modern organisms may have evolved from or share a common ancestor with ancient organisms
How can natural selection lead to evolution? (2)
- it causes gradual changes
- over a long period, can lead to the development of a new species
