Variation and Speciation Flashcards
what does variation mean?
-the differences in physical characteristics between organisms within the same species
what type of genotype allows for variation?
-heterozygotes
what are the 3 ways that genetic variation can be maintained?
-genetic and environmental factors
-meiosis
-gene mutations
what are the 2 types of variation and what are2 examples of each?
-discontinuous= being male or female, or having or not having ear lobes
-continuous= height, weight
what 2 things that affect continuous variation?
-genetic and environmental factors
what are the 3 ways that meiosis leads to genetic variation?
-independent assortment along the equator at metaphase one
-random fertilisation to produce a random zygote
-crossing over of genes/ chisamata formation where one gene is switched with the corresponding gene on the other chromosome
what can crossing over of chromosomes result in?
-an entirely new allele combination that were not present in the paternal chromosomes
what is another process that can result in spontaneous variation?
-chromosome and gene mutations
what is the definition of a mutation?
-a permanent change to the DNA in an organism
what causes a gene mutation?
-a change in the sequence of bases in the DNA
what is the consequence of a single base mutation in terms of the codon and protein produced?
-if one base changes then the codon changes which codes for a different amino acid, therefore a different polypeptide and eventually a different protein
what are the three types of gene mutations?
-base substitution
-base deletion
-base insertion
what is base substitution? what is the result of this and what is the term to describe the effects of this mutuation?
-when once base replaces another
-this will change is limited to one amino acid
-neutral mutation
what is base deletion/ insertion? what does this cause to happen and what is the term to describe this?
-when a base is removed or added
-it changes the base triplet as well as the rest of the gene
-frame shift
what do chromosome mutations involve?
-changes to large sections of DNA containing several genes
what are the two type of chromosome mutations?
-aneuploidy
-polyploidy
what is an aneuploidy chromosome mutation involve? how many chromosomes will a zygote therefore contain? what is an example of a condition caused by this?
-when one chromosome fails to separate at anaphase 1
-47
-Downs Syndrome
what is polyploidy chromosome mutations? what organism are they common in?
-mutations where whole sets of chromosomes fail to separate
-plants
what is one environmental factor that can encourage these mutations?
-UV exposure
what does selection pressure mean?
-external agents that affect an organisms ability to survive and they can be positive or negative
what is survival of the fittest?
-the better adapted organism to the environment will be the one who survives and outcompetes the less adapted
who came up with the theory for natural selection?
-Darwin
how does the genetic makeup of a population change over time?
-due to particular alleles increasing in frequency while other reduce due to not surviving in a certain environment
what is the term to describe how selection is influenced by the environment?
-environmentally dependent
what type of variation must occur to result in a change in a population or a species?
-both genetic and environmental
what does fitness mean in terms of selection?
-how well an organism is adapted for its environment
-selection favours the fitter organisms against those who are less fit
what does differential reproductive success mean?
-if the better adapted individuals survive then they will produce offspring which are also better adapted
-the less adapted are killed and so the frequency of their alleles decrease as they are outcompeted
what are the 2 types of selection and what do they involve?
-stabilising selection
-directional selection
what does stabilising selection mean and what individual is best adapted? what type of environment does this occur in?
-it shows normal distribution
-the average phenotypes are best suited whereas the extremes of individuals are less well adapted
-occurs in unchanging environments
what happens as consequence of the average individuals surviving during stabilising selection?
-they pass their genes onto their offspring
look at graph of stabilising selection
-fsf
why does stabilising selection not cause evolutionary change?
-because in highly adapted populations in stable ecosystems it will appear that selection is not occurring because there is not obvious changes in the phenotype over time
what are the best adapted individuals in directional selection?
-those whose phenotypes lie closer to the extremes of variation
where are the two places where directional selection is most likely to take place?
-changing environment
-population colonies in a new habitat
how is pesticide resistance in insects an example of directional selection?
-this resistance is caused by mutation
-if insects subjected to pesticides this mutation offers subjective adaptive advantages
-these will survive and pass their resistant genes onto their offspring
-resulting in the frequency of this allele increasing and eventually the entire population will become resistant
what is the selectional pressure which causes antibiotic resistance?
-the over use of bacteria
does directional selection cause evolutionary change?
-yes
what does polymorphic mean?
-population where there is more than one alternative for a particular trait
-there are two or more genotypes that produce the same phenotype
what are three examples polymorphisms in organisms?
-human blood groups
-eye colour
-banding in snails
what is definition of species?
-a group of individuals of common ancestry that are normally capable of interbreeding to produce fertile offspring
what is the definition of speciation?
-the formation of new species that are reproductively isolated from other species
what must occur in order for animals to create a new species?
-reproductive isolation
what are the 3 factors that cause reproductive isolation? what does each of these mean?
-geographical separation= population of same species live in different parts of the world
-habitat isolation= same species lives in different parts of the same habitat
-temporal isolation= same species live in same habitat but are reproductively active at different times
what are the two types of speciation?
-allopatric speciation= geographical
-sympatric speciation= reproductive
what is the process of allopatric speciation?
-starts with an interbreeding population of one species
-population becomes divided by a physical barrier e.g. geography changes like an earthquake, or due to migration
-if the two new environments are different then the two species will evolve differently due to different selectional pressures
-even if the barrier is removed the two populations are now so different they can no longer interbreed
-they are now reproductively isolated
what is a consequence to the original species if it is well adapted to its original environment if it is separated by allopatric speciation?
-if the environment changes the the species must adapt or die
-this could result in the original species becoming extinct
what is sympatric speciation? what are the 2 causes of this speciation?
-when a population is reproductively isolated within the same environment which is caused by reproductive seasons being different or living in different areas (niches)
