Topic 7 Genetics, populations, evolution and ecosystems

Genotype

all the alleles that an organism can carry on its chromosomes

Phenotype

the observable characteristics of an organism, resulting from the genotype and the environment

Dominant

one allele needs to be present to be visible in the phenotype

Recessive

two recessive alleles need to be present to be expressed in the phenotype

Codominant

both alleles are dominant, so both are expressed in the phenotype

Loci

a position on a chromosome where are specific gene is present

Sex linkage

some traits only present on the X chromosome, therefore males are more likely to be affected by a recessive allele

Autosomal linkage

when two genes are on the same loci, so crossing over unlikely to occur so are inherited together

Epistasis

one allele effects the presentation of another allele, therefore can mask or supress another allele

Population

a group of organisms of the same species occupying a particular space at a particular time

Gene pool

the total number of alleles present in a population

allelic frequency

percentage of a certain allele in a gene pool

What is assumed whilst using the Hardy Weinberg equation

• no mutations occur to create new alleles

• no movement of alleles into or out of population by migration

• the population is large

• no selection

• mating is random

Niche

a species role within an environment

Intraspecific competition

competition within a species for food, mates etc

Directional selection

occurs when the environment conditions change and the phenotype best suits the new conditions

Stabilising selection

the phenotypes with successful characteristics stay perserved

Disruptive selection

both extremes are favoured over the mean

speciation

process of a new species arsing after a population becomes seperated and cannot interbreed

Ecosystem

all the organisms living in a particular area as well as the non-living elements

community

all the living organisms in an area

interspecific competition

members of different species compete with one another for the same resources

succession

the change of one community of organisms into the other

Primary succession

• occurs when area has no life and is colonised by a pioneer species which can live in harsh conditions

• environment becomes less hostile so other organisms can live

• eventually climax community occurs

Secondary succession

• in a previously colonised area in which an existing community has been cleared

• then like primary succession

Climax community

the stable community of organisms that exists at the final stage of ecological succession

Allopathic Speciation

Geological isolation

Sympathetic speciation

No physical barrier, eg reproductive barrier