factors affecting allele frquency

doesn't include mutations

define gene pool

The sum of all the alleles carried by the members of a population

define allele frequency

how often each allele of a gene occurs in a population

what can affect allele frequency in a population’s gene pool

• evolutionary mechanisms (natural selection)

• chance occurrences (mutations, founder effect and random genetic drift)

define variation

the differences that exist between individuals/populations of a species

define natural selection

The process by which a species becomes better adapted to its environment; those individuals with favourable characteristics have a survival advantage and so pass those characteristics on to subsequent generation

define evolution and what causes evolution

• Evolution = the gradual change in the characteristics of a species

• natural selection selects among whatever variations exist in the population which results in evolution

explain the principle of evolution through natural selection - VOSSIC / what are the features required for natural selection to occur?

1. Variation in characteristic of species

2. offspring - more offspring produced than can survive, due to excessive birth rate & limited resources there’s a struggle for existence / competition for survival 

3. Survival of the fittest & Suitability - individuals with characteristics better suited to environment have more chance of reproducing 

4. Inheritance - favourable characteristics passes on next generation

5. Characteristics - gene pool will have a higher proportion of alleles that produce favourable characteristics 

explain how a large population influences evolution

• More variations in the gene pool

• individuals make only a small contribution to the gene pool

• Evolutions occur slowly

• Most changes are adaptive

• Natural selection is the main driving force

explain how a small population influences evolution

• Less variation in the gene pool

• Individuals make a relatively large contribution to the gene pool

• Evolution occurs rapidly

• Many changes are non-adaptive

• Many changes are due to chance events

define an adaptation

Any characteristic that helps an organism to survive & reproduce in its environment

give examples of adaptations

1. Body shape & structure to survive hot & cold climates - allen’s rule (body shape & surface area)

2. Sickle cell to survive malaria - heterozygous for sickle cell gene - less susceptible to malaria

3. Skin colour to survive harmful UV radiation - dark skinned people have more melanin in their skin than light-skinned people have

define gene flow

movement of genetic material from one population to another

define migration

the movement of people from one area to another with the intention of settling permanently

Explain how barriers affect gene flow, what does isolation lead to & what are the 2 classifications for barriers?

• Populations kept apart by barrier that inhibit amount of interbreeding between them

• Isolation leads to separate gene pools forming

• Barriers are classified based on their cause: geographical or sociocultural

identify geographical barriers

• Oceans 

• Mountain ranges

• Large lake systems

• Deserts

• Expansive ice sheets

identify sociocultural barriers

• Economic status

• Educational background

• Religion

• Social position

• Language

define (random) genetic drift

The occurrence of characteristics in a population as a result of chance rather than natural selection; occurs only in small populations; also called genetic drift or Sewall Wright effect

explain founder effect

• Extreme example of genetic drift

Occurs when a small group moves away from its homeland to a totally new are & establishes a population which later expands

Book definition: A type of genetic drift where a new population is formed by a small number of individuals; the small sample size can cause marked deviations in allele frequencies from the original population

what happens to a founder population - compare it to original population

Due to small size, chance can cause the new group to have:

• A different allele frequency from the original population

• Decreased genetic variation

• New population may not show a frequency of feature that are not typical of the original homeland population

explain bottle neck effect

• An extreme form of genetic drift that occurs when the size of a population is severely reduced due to a sudden event such as a natural disaster.

• The allele frequency of survivors may not reflect that of the original population (chance)

• NOTE: survival of event is due to chance NOT having specific trait

define species

a group of individuals that share many characteristics (the basic unit of biological classification) & are able to interbreed under natural conditions to produce fertile offspring

define speciation

the process of new speices developing

identify 4 stages of speciation - (the 4th stage being speciation)

1. Variant

2. isolation

3. Selection

4. Speciation

define selective agents

Any factor that causes the death of organisms with certain characteristics, but which has no effect on individuals without those characteristics

explain the process of speciation

• Reproductive isolation may lead to development of separate gene pools

• No 2 environments are exactly the same so certain alleles would be favoured in 1 environment more than another

• Over many generations allele frequencies of each gene pool will change depending on which characteristics are favoured for survival

• The populations will become less & less alike

• Members of these populations may become so different that if barrier to reproduction is remove interbreeding would no longer be possible

• If this occurs the 2 populations are regarded as separated species