evolution

mutation

permanent change in an organisms dna. this can cause a gene to code for a different protein/ trait. they occur without known cause - mutagens can increase rate at which they occur

somatic and germline mutation

somatic occur in single body cell and cannot be inherited as only tissue derived from mutated cell effected

germline mutations occur in gametes and can be passed onto offspring where every cell in the entire organism is affected

point mutation - subsitution

mutation that may create either a silent, missense or nonsense mutation depending on how change impacts polypeptide sequence

silent mutation occur when the dna change does not alter the amino acid sequence of polypeptide

missense mutation occur when dna change alters a single amino acid - sickle cell anemia

nonsense mutation occur when dna change creates a premature stop codon which truncuate polypeptide - cystic fibrosis

frameshift mutation - insertion or mutation

addition or removal of a single base of dna changing reading frame. this change affects every codon beyond point of mutation and thus may dramatically change amino acid sequence. hence, frameshift mutation typically have significant impact on cellular activity as there is a high likelihood the polypeptide will cease to function

chromosomal mutation - large scale insertion, duplication, deletion, inversion, translocation

changes to segment of chromosome resulting in large scale changes in dna of organism

non disjunction

chromosomes fail to separate correctly, resulting in gametes with one extra or missing chromosome (aneuploidy)

failure of chromosome separation occur via failure of homologues to separate in anaphase 1 or failure of sister chromatids to separate in anaphase 2

mutagen examples

mustard gas, formaldelhyde, ionising radiation like uv, xray, cosmic ray. radiaction from radioactive waste.

if a pregnant woman treated with a large dose of x ray in the first 3 months the baby may be born with intellecutal disability, skeletak malformation, microcephaly

evolution

change in allele frequency in populations over time.

the phenotypes of individuals are a result of genotype of each trait

causes of evolution

genetic mutation, gene flow, sexual selection, decreasing population

natural selection - random

gene flow

exchange of alleles between two or more populations. when migrating animals often carry new alleles from one population to another and must interbreed with the new population for gene flow to occur

sexual selection

species choose mate based on arbitary factors

decreasing population or genetic drift

reduction of population

may cause gene variants to disappear completely and thereby reduce genetic variation, cause initially rare alleles to be more frequent

bottleneck effect

original population has approximately equal frequency of red and yellow alleles

a chance environmental event greatly reduces population size

allele frequency in surviving population is different from those in original population

as population grows following bottleneck event its allele frequency reflects the surviving population

example of bottleneck

island of pingelap suffered population bottleneck in 1775 following typhoon reducing the population to 20 people. as a result complete achromatopsia has current rate of occurrence at roughly 10% with additional 30% being carriers of recessive condition

founder exmaple

amish community in pennsylvania have high rates of certain inherited disorders like ellis van creveld syndrome

natural selection

non random selection of random variations which occur via mutations

charles darwins 3 assumptions

1. variation: all members of a species vary. these variations were passed on from one generation to the next.

2. birth rate: all living organisms reproduce at a rate far greater than that at which their food supply and other resources increase leading to overcrowding and competition

   1. natures balance: although birth rate of organisms was very high, each species numbers tended to remain at a relatively constant level

selection pressures

predator, availability of resurces, nutrient supply, disease/ pathogen spread, abiotic factors - temp, c02 levels

principal of evolution

variation: there is variation of characteristics within a species

overpopulation: more offspring of a species are produces than can possible survive to maturity

competition: there is a struggle for existence some will not survive to reproduce

survival of the best fit: individuals with characteristics best suited to that environment have more chance of surviving and reproducing due to selection pressures

inheritance: favourable characteristics are passed onto next generation

change in allele frequency: in the gene pool the proportion of alleles that produce favourable characteristics gradually increase

explain how a feature would have become more common in the population over time (7)

1. variation in presence of —- would have existed in the population

2. there would be a struggle for existence in —- due to more offspring being produced than can survive to maturity

3. those with —- would have been able to —-

4. and would have survived selection pressures and reproduce due to survival of the fittest

5. passing on allele for —- to offspring

6. those without —- wouldve died or failed to reproduce

7. so over time the population would become more alike with —-