Flashcards in 7. Variation Deck (20):
What is it called when one species differs from another?
Can members of the same species differ from each other?
Yes, members of the same species can differ from each other, it is called intraspecific variation.
Why is it difficult for biologists to make measurements of organisms and how do they avoid this problem?
It is difficult because they are usually measuring some aspect of living organisms and all living organisms are different. They take samples.
Sampling involves taking measurements of individuals, selected from the population of organisms which is being investigated.
Why are some samples not always representative of the whole population?
Sampling bias: the investigator could be making bias choices.
Chance: even if bias is avoided, the individuals chosen might not be representative by pure chance.
How can we prevent sampling bias?
Eliminate any human involvement in choosing the samples. This is achieved by carrying out random sampling.
Give one method of random sampling?
1. Divide the area into a grid of numbered lines. E.g by stretching two long tape measures at right angles to each other.
2. Using random numbers, from a table or generated by a computer, obtain a series of coordinates.
3. Take samples at the intersection of each pair of coordinates.
Can we completely remove chance from a sampling process?
No, but we can minimise it.
How can we minimise chance from a sampling method?
By using a large sample size: the more individuals selected the smaller the probability that chance will influence the result. The greater the sample size the more reliable the data will be.
Analysis of the data collected: accepting that chance will play a part, the data collected can be analysed using statistical tests to determine the extent to which chance may have influenced that data. They allow us to decide whether any variation observed is the result of chance or is more likely to have some other cause.
What are two causes of variation?
Genetic differences and environmental influences.
What causes genetic differences?
The different genes that each individual organism possesses.
What are the three causes of genetic variation?
Mutations: these sudden changes to genes or chromosomes may, or may not, be passed on to the next generation.
Meiosis: this special form of nuclear division forms the gametes.this mixes up the genetic material before it is passed into the gametes, all of which are therefore different.
Fusion of gametes: in sexual reproduction the offspring inherit some characteristics of each parent. Which gamete fuses with which at fertilisation is a random process, further adding to the variety of offspring parents can produce.
How can asexually reproducing organisms increase variation?
By mutation only.
Populations of sexually reproducing organisms are more ................ than asexually reproducing organisms.
Populations of sexually reproducing organisms are more varied than asexually reproducing organisms.
How do environmental influences change the way an organisms genes are expressed?
Environmental influences set limitations on how genes are expressed e.g a child growing shorter than the limit of its genes because of malnutrition.
Give some examples of environmental influences.
Climatic conditions, soil conditions, pH and food availability.
It is difficult to draw conclusions about...
The causes of variation in any particular case - they are usually a mixture of genetic differences and environmental influences. Any conclusions drawn should be treated with caution.
What kind of graph is produced form variation due to genetic factors?
Bar chart or pie graph.
(Organisms fit into a few distinct forms and there are no intermediate types.)
What kind of graph is produced form variation due to environmental influences?
A bell-shaped curve, known as a normal distribution curve.