7. Genetics, populations, evolution and ecosystems

• genotype: the genetic constitution of an individual organism.
• phenotype: the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.
• dominant is an allele whose characteristics appears in the phenotype even if there is only one copy
• recessive is an allele whose characteristics only appears in the phenotype if two copies are present
• the locus is the fixed position of a gene on a chromosome
• codominant is when two dominant alleles are expressed
• homozygote is when an individual has two identical alleles for a particular gene
• heterozygote is when an individual has two different alleles for a particular gene
• aa carrier is someone carrying an allele which is not expressed in the phenotype but can be passed onto offspring
• alleles are sex linked when the allele that codes for it is located on the sex chromosome
• an autosomal gene is any chromosome that isn't a sex chromosome
• an autosomal linkage may have ocured if the phenotypic ratio is different to the expected
• an epistatic gene masks the expression of another gene
• a chi-squared test is used to test for differences between two populations and is used to test for differences between two samples
• the null hypothesis is the assumption that there is no significant difference between the observed and expected results
• in the Hardy-Weinberg principle it predicts that the frequencies of alleles in a population won't change from one generation to the next
• what conditions are needed to use the Hardy Weinberg principle?

  Large population, random mating, no migration, no mutation, no natural selection.
• what equation can be used to predict allele frequency?

  p + q = 1
• what equation can be sued to predict phenotype frequency?

  $p^2 +$$2pq +$$q^2 =$$1$
• what is the main source of variation?

  mutations
• evolution is a change in allele frequency over time
• stabilising selection is where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce
• when does stabilising selection occur?

  when the environment isn't changing
• directional selection is where individuals with alleles for a single extreme phenotype are more likely to survive and reproduce
• when does directional selection occur?

  when the environment is changing
• disruptive selection is when individuals with alleles for extreme phenotypes at either end of the range are favoured and characteristics towards the middle of the range are lost
• when does disruptive selection occur?

  when the environment favours more than one phenotype
• speciation is the development of new species from existing species
• speciation occurs when populations of the same species become reproductively isolated and changes in allele frequency cause changes in phenotype leading to them no longer being able to interbreed to produce fertile offspring
• allopatric speciation occurs due to geographical isolation
• allopatric speciation leads to both populations experincing different selection pressures
• sympatric speciation occurs without geographical isolation
• what are 3 possible causes of reproductive isolation?

  seasonal, mechanical, behavioural
• genetic drift is the random change in allele frequency in a population due to chance
• a habitat is the place when an organism lives
• a population is all the organisms of one species in a habitat
• a community is all the populations of different species in a habitat
• an ecosystem is the community and all the abiotic conditions in an area
• abiotic conditions are the non living features of an ecosystem
• biotic conditions are all the living features of an ecosystem