4.4 variation and evolution

define variation

differences between individuals of the same species

list the reaons why organisms phenotypes might differ

DNA inherited

environment

epigenetics

mutation

what is heritable variation?

differences in phenotype due to genetic reasons

can be inherited

how does sexual reproduction cause heritable variation?

crossing over in prophase I of meiosis

random assortment of homologous chromosomes in metaphase I

random assortment of chromatid pairs in metaphase II

random fertilisation between 2 haploid gametes

what is non-heritable variation?

variation caused by differences in environment

cannot be inherited

no effect on gene pool

how can variation be described?

discontinuous

continuous

what is discontinuous variation?

do no show complete gradation

phenotypes in discreet groups

monogenic - controlled by 1 gene

environment has no effect on gene expression

phenotypes represented on bar/pie charts

what is continuous variation?

phenotypes show complete gradation

gradations from one extreme to the other

polygenic - controlled by many genes

environment has considerable influence on gene expression

what are examples of continuous variation?

human height

plants needing light for growth and development

how is human height an example of continuous variation?

individuals inherite alleles from parents

alleles determine potential maximum height

whether potential is reach dependent on environmental factors

what environmental factors affect human height?

nutrition

excerise

how is plants needing light for growth and development an example of continuous variation?

without light, auxin synthesis elongates stem cells

unable to synthesise chlorophyll

seed germinated in dark - seedling is etiolated

what is an etiolated seedling?

it shows chlorosis and grows taller than in presence of light

what is environmental resistance?

any factor that limits population/carying capacity

what types of competition are there?

interspecific

intraspecific

what is interspecific competition?

competition between different species

what is intraspecific competition?

competition within the same species

what is selection?

the process by which organisms that are better adapted to their environment survive and breed, passing on theur advantageous alleles/mutation to their offspring

define selection pressures

factors that determine which organisms are better adapted to their environment

what are examples of selection pressures?

supply of food

breeding sites

camouflage

availability of breeding partners

what happens if a phenotype has a selective advantage?

the alleles responsible for the phenotype will be selected for

more likely that they will be passes on to next generation

frequency of that allele will increase in the gene pool

what happens if a phenotype has a selective disadvantage?

alleles responsible for the phenotype will be selected against

less likely to be passes on to next generation

frequency in gene pool will decrease/be lost entirely

define gene pool

all the alleles of all the genes in the genome

what does population genetics describe?

the behaviour of genes and alleles within a population in terms of allele frequency and how they change over time

what can the gene pool be describes as?

fluid

constantly changing

what is genetic drift?

variation in populations occuring by chance

important in small or isolated populations

what is the bottleneck effect?

extreme example of genetic drify

occurs after natural disasters

what happens to the allele frequencies as a result of genetic drift?

very different from original population

some alleles may be missing entirely

population more susceptible to the effects of genetic drift

what is the found effect?

extreme example of genetic drift

when a small group of individuals breaks off from a larger population to establish a colony

what is the new colony produced from the founder effect?

isolated from the original population

founding individuals may not represent full genetic diversity

what happens to the allele frequencies as a result of the founder effect?

alleles present at different frequencies

some may be missing all together

what is the hardy-weinberg principle?

in ideal conditions, dominant and recessive allele frequencies remain constant from one generation to another

what are the ideal conditions for the hardy-weinberg principle:

the organism

diploid

allele frequency equal in both sexes

repride sexually

MATING RANDOM

generations do not overlap

what are the ideal conditions for the hardy-weinberg principle:

the population

large (>100 individuals)

no migration

no mutation

no selection for or against any phenotype

in the equation p2 + 2pq + q2 = 1

what does p stand for?

frequency of the dominant allele

in the equation p2 + 2pq + q2 = 1

what does q stand for?

frequency of the recessive allele

in the equation p2 + 2pq + q2 = 1

what does p2 stand for?

frequency of AA - homozygous dominant

in the equation p2 + 2pq + q2 = 1

what does 2pq stand for?

frequency of Aa - heterozygous

in the equation p2 + 2pq + q2 = 1

what does q2 stand for?

frequency of aa - homozygous recessive