biology topic 8

factors that increase genetic variation

Mutations

Random assortment and crossing over during meiosis

Random fertilisation during sexual reproduction

mutation

alteration in base sequence during DNA replication

why might a mutation not occur in a change

genetic code is degenerate so could code for same amino acid unless frame shift occurs

addition and deletion mutation

deletes or adds base to sequence causing frame shift and changing entire sequence

Subsitution mutation

one or more bases are changed doesnt cause frame shift

quiet mutation

how does meiosis create new combinations of alleles

random arrangement of chromosomes when lining up

crossing over of chromatids before division

genotype

genetic makeup of an organism

phenotype

physical characteristics of an organism

allele

Different forms of a gene at same position on chromosome

dominant allele

allele that will always show in the phenotype whether there is one or two

recessive allele

allele will only show in phenotype if no dominant allele is present

codominant allele

two allele that both show in phenotype by blending or appearing together

homozygous

both allele are the same dominant or recessive

heterozygous

alleles are different one is dominant one is recessive

multiple alleles

gene with more than two alleles

how are non interacting unlinked genes inherited

monohybrid or dihybrid

monohybrid

phenotypic characteristic controlled by a single gene

dihybrid

two phenotypic characterisitics are controlled by two different genes on two different chromosomes

autosomal linkage

two or more genes on the same chromosome only one pair needs to be present for all four alleles to be present

example of autosomal linkage

Drosophila in fruit flies

colour and wing length

they are inherited in pairs

why are autosomally linked genes are inherited in pairs

genes on same chromosome are close together so less likely to undergo recombination in meiosis

sex-linkage

when allele is located on sex chromosome meaning its expression depends on the sex of the individual

why are men more likely to express a recessive sex linked allele

most sex linked alleles are located on X chromosome so they only get one copy or allele meaning it will be shown even if its recessive

chi- squared test

statistical test to determine whether difference between expected and observed data is due to chance

criteria for chi- squared test

data in discrete catagories

large sample size

only raw data allowed

no data values zero

population

all the organisms of a particular species that live in the same place

selection pressures

predators

disease

competition

environmental conditions

how do selection pressures change allele frequencies within a population

organisms with advantageous characteristics ae more likely to survive and produce offspring

stabilising selection

occurs when environmental conditions stay the same

any new characteristics ae selected against

results in low diversity

disruptive selection

both extremes of normal distribution are favoured over mean.

population becomes phenotypically divided and new species might develop

genetic drift

change in populations allele frequences that occurs due to chance rather than selective pressures

population bottle neck

event that reduces the size of a population and decreases the varity of alleles in the gene pool causing changes in allele frequencies

founder effect

a small number of individuals become isolated forming a new populatopn with a limited gene pool

alleles frequences not reflective of orginial population

hardy- weinberg principle

allows us to estimate the frequency of alleles in a population as well as if allele frequence is changing over time

assumptions of Hardy- weinburg principle- mutations

no mutations occur to create new alleles

assumptions of Hardy- weinburg principle- migration

no migration in or out of the population

assumptions of Hardy- weinburg principle- selection

no selection so alleles are all equally passed on to the next generation

assumptions of Hardy- weinburg principle- mating

random mating

assumptions of Hardy- weinburg principle- population

large population

hardy weinburg equation for allele frequency

p + q = 1

what does p mean

frequency of dominant allele

what does q mean

frequency of the recessive allele

hardy weinburg equation for genotype frequencies

p2 + 2pq + q2 = q2

what does p2 mean

frequency of homozygous dominant

what does 2pq mean

frequency of heterozygous

what does q2

frequency of homozygous recessive