VARIATION

VARIATION

Presence of diff characteristics and this leads to diff survival rates. Diff between individuals of the same species.

This is needed for natural selection to occur

Types of variation

Continuous or discontinuous

Genetic or phenotypic

Discontinuous

Variation which can only take particular values- gender, shoe size. Controlled by 1/few genes. Environmental- little effect on these characteristics. Qualitative diff in phenotypes of individuals

Discrete

Continuous variation

Variation within a range and is measurable- height, mass, length of index finger

It’s polygenic + controlled by the environment.

Quantitative diff in phenotypes of individuals.

Normal distribution curve

Genetic variation

Diff between DNA base sequences of individuals within a species.

Phenotypic variation

Diff between the observable characteristics of individuals within a species.

Polygenes

A no of diff genes at diff loci that all contribute to a particular aspect of phenotype.

Genetic basis of discontinuous variation

Variation only occurs due to genetic factors. Diff alleles at a single gene locus have a large effect on the phenotype.

Example: F8 Gene codes for blood clotting protein factor VIII. Diff alleles in this gene locus dictate whether or not normal Factor VIII is produced and if the person has haemophilia.

Genetic basis of continuous variation

Only caused by an interaction between genetics + environment

PHENOTYPE= GENOTYPE + ENVIRONMENT.

Eg height- genes inherited that affect growth which interact w lifestyle factors- diet.

Genetic level- discontinuous variation

Diff alleles on the same locus have a large effect on the phenotype

Diff genes have quite different effects on the phenotype

Genetic level- continuous variation

Diff alleles at a single locus have a small effect on the phenotype.

Diff genes can have the same effect/ hv a large effect on the phenotype and these add together to have an ADDITIVE EFFECT.

If. A large no. Of genes have a combined effect on the phenotype- polygenes

Genetic variation- process

Mutations- that affect mitotic cell cycle.

Cell divides uncontrollably- lead to a development of a tumour.

Mutations in cells in ovaries/testes- can be inherited by offspring.

Variation caused by the environment- not passed onto the offspring

Variation T-test method

Compare the means of 2 diff sets of data to see if they are sig diff.

Data should be continuous, normally distributed + sample size should be between 10-30 readings for set.

Formula For T-test

X1= mean of sample 1

X2= mean of sample 2

N1/N2- no of individuals measurements in sample ½

S1²= standard deviation of sample 1 squared

S12²= standard deviation of sample 2 squared

Standard deviation

Null hypothesis

Baseline assumption- no sig diff

STEPS OF T-TEST

1. State null hypothesis

2. Carry out test

3. Degrees of freedom (V)

4. Look at the table then value of t. If val of t> critical val= reject null hypothesis.- means there is a sig diff between the 2 sets of data

Degrees of freedom (V)

(N1-1)(n2-1)

P values

Probability that could have produced the results observed