Variation (UNIT 2) Flashcards
INTERSPECIFIC VARIATION
differences between organisms of different species.
INTRASPECIFIC VARIATION
differences between organisms of the same species
What is sampling?
Involves taking measurements of individuals, selected from the population of organisms which is being investigated.
IN THEORY, if these individuals are representative of the population as a whole, then the measurements can be relied upon.
Two reasons why sampling measurements may not be representative.
SAMPLING BIAS- Selection process may be biased. Investigators may make unrepresentative choices, either deliberately or unwittingly.
CHANCE- Even if sampling bias is avoided, the individuals chosen may, by chance, not be representative.
How to prevent sampling bias.
Eliminate, as far as possible, human involvement in choosing samples. BY RANDOM SAMPLING.
METHOD:
1. Divide study area into grid of numbered lines.
2.Using random numbers, from a table or generated by computer, obtain a series of coordinates.
3.Take samples at the intersection of each pair of coordinates.
How to minimise chance from sampling process.
- Use large sample size- The more individuals selected the smaller the probability that chance will influence result.
- Analysis of data collected- The data collected can be analysed using statistical tests to determine the extent to which chance may have influenced the data. Allows you to determine whether any variation observed is due to chance or more likely another cause.
What two main factors affect variation?
Genetic differences and environmental factors.
What are genetic differences?
Due to different genes that each individual organism possesses. Differences not only arise in living individuals but also change from gen to gen.
What 3 things result in genetic variation.
MUTATIONS- These sudden changes to genes and chromosomes may, or may not be passed on to the next generation.
MEIOSIS- Forms gametes. Mixes up genetic material before it is passed into the gametes, so all are different.
FUSION OF GAMETES- In sexual reproduction offspring inherit some characteristics from each parent and are therefore different from both. Random mix of two gametes which further adds to variety off offspring possible.
In asexually reproducing organisms what is the only way variety can occur?
MUTATIONS
How does the environment an organism lives in affect its genes?
Affect how genes are expressed. Gene sets limits, but largely the environment that determines where, within those limits, an organism lies.
What are examples of environmental influences?
Climatic conditions (temperature, rainfall, sunlight)
Soil conditions
pH
Food availability.
Describe variation due to genetic factors.
Characteristics fit into a few distinct forms and there are no intermediate types.
A character displaying this type of variation is usually controlled by a single gene.
Environmental factors have little influence on this type of variation.
eg. blood type
Describe variation due to environmental factors.
Some characteristics of organism grade into one another, forming a continuum. eg height and mass in humans.
NOT CONTROLLED BY ONE GENE BUT MANY (polygenes).
E Factors play major role in determining where on the continuum an organism actually lies.
What is the mean of a sample of data?
average value. useful when comparing one sample with another.
DOES NOT PROVIDE INFO ON RANGE OF VALUES WITHIN SAMPLE.
