Variation Flashcards
Interspecific variation
Between species
Intraspecific variation
- within species
- same genes, different alléles
- May be caused by genetic or environmental factors (can change phenotype)
- mutations may result in the change or loss of a protein
Sampling
- taking a small sample of the population
* multiple measurements allow reliable, valid conclusions
How to take a sample
Take a selection of individuals from the population that will provide an accurate representation of the entire population; normally done by random sampling
Issues with sampling
sampling bias -> investigators may be making unrepresentative choices, either deliberately or unwittingly
chance -> individuals chosen may not be representative
Random sampling
• aims to prevent bias and eliminate human involvement in choosing samples
1) divide the area of study into a grid
2) use a random number generator to chose coordinates
3) take samples from the intersection of coordinates
Removing chance
- large sample size > 20
- smaller propability of chance influencing result, less anomalies -> increasing reliability
- use statistical tests to analyse data, determining extent of chance’s influence
Continuous variation
- the full range of variables between 2 extreme values
- data is normally distributed in a Normal Distrubution
- mean, mode, median are equal
- e.g. height, weight, length, size
- phenotype either polygenic, causes by environmental factors, or both
Normal Distribution
Bell shaped curve
Discontinuous variation
- aka discrete
- unaffected by environment, controlled by few genes
- variables assigned to clearly defined categories/distinct groups
- data usually represented as a bar graph
- e.g. sex, blood group, colour
Standard deviation
- the distance from the mean to the point where the curve changes from concave to convex
- 68.2% of measurements lie within +-1 standard deviation
- 95% lies within +-1.96
- gives an indication of the range of values either side of the mean
