Mechanisms of evolution Flashcards
define evolution
gradual change in the characteristics of a species
population
group of organisms of the same species living together in a particular place at a particular time
allele
alternate form of a gene
gene pool
sum of alleles in a given population
allele frequencies
how often each allele of a gene occurs in the gene pool of a population
point mutations
change to a single nucleotide
- insertion
- substitution
- deletion
may result in a frameshift
eg sickle cell anemia
define frameshift
mutation involving an insertion or deletion that results in a change in the way that the sequence is read
gene mutation
changes in a single gene so traits normally produced by that gene are changed or destroyed
eg CF
chromosomal mutations
part of or all of the chromosome is affected
- duplication
- deletion
- inversion
- translocation
- non-disjunction (aneuploidy)
eg of chromosomal mutations
down syndrome (trisomy-21)
patau syndrome (trisomy-13)
klinefelter syndrome (XXY,XYY)
cri-du-chat syndrome (partial monosomy 5)
turner syndrome (X)
common symptoms: early death, intellectual disability etc
mutagens
agents that increase rate of mutation, eg ionising radiation, formaldehyde, mustard gas
how do mutagens cause changes to DNA
- resemble proteins and be incorporated into DNA
- chemically react with and modify DNA
- cause DNA breakages
- trigger replication errors
somatic vs germline mutations
somatic: body cells that are not reproductive cells are affected, cannot be passed down, often cancerous
germline: reproductive cells affected, can be passed down
eg PKU, muscular dystrophy, CF, Tay-sachs
effect on amino acids and protein
missense: change in amino acid and hence protein
nonsense: short protein
neutral: change in amino acid, not really protein produced
silent: no change in amino acid
lethal recessive
recessive mutations that are lethal if not masked by the dominant allele
genetic drift
random, non directional change in allele frequencies of a population between generation
- unlikely to have a significant impact on a large population, but more significant impact on small population
- random small sample of population not genetically representative of whole population
why is random genetic drift more significant in small populations than large populations
less variation in small populations, less ability for small population to respond favourably to changing conditions
founder effect
small group moves away from homeland and establishes a new population, with different allele frequencies compared to the original population
- decreased genetic variation in the population
- new population show a frequency of features not typical of the homeland population
gene flow and migration
gene flow: movement of genetic material from 1 population to another
migration: movement of individuals between populations to enable gene flow
- will cause frequencies of alleles to be altered between the 2 populations, may even introduce new alleles into population
advantage to blocking gene flow
high incidence of lethal recessive gene in a population, benefit to limit gene flow to not influence gene pools of other populations
disadvantage to blocking gene flow
inbreeding occurs in isolated populations, frequencies of unusual characteristics much higher
natural selection
- natural selection is the process by which the proportion of alleles producing favourable characterisitcs gradually increases in a population over several generations
1) there is variation within a species
2) overproduction of offspring that can possibly survive to maturity
3) excessive birth rate, limited resources, there is a struggle for existence
4) individuals with characteristics best suited for the environment have more chance of surviving and reproducing (survival of the fittest
5) favourable characteristics are passed on to the next generation
6) proportion of alleles that produce favourable characteristics gradually increase OVER SEVERAL GENERATIONS
define selection pressure
environmental factor acting on population
species
group of individuals that share many characteristics and are able to interbreed to produce fertile offspring
describe speciation
1) varation
- range of varations exist within the population which shares a common gene pool
2) isolation
- barrier has formed, dividing the population into 2
- no interbreeding between the 2 populations, each population has a separate gene pool
3) selection
- different selection pressures act on each of the 2 populations OVER SEVERAL GENERATIONS
- change in allele frequencies of each gene pool, leading to evolution of subspecies
4) speciation
- over a long period of time, changes in gene frequency that when there is interbreeding between these 2 populations, fertile offspring can no longer be produced
- 2 species exist
how does errors in DNA replication result in mutation?
replication: process where new strands of DNA are produced
- complementary strands are formed
- errors include subsitution, insertion, deletion, frameshift, alter DNA code
- DNA formed undergoes cell division to create a new cell
- new cells have the wrong DNA code
how does errors in cell division result in mutation?
- homologous chromosomes line up
- genetic material swapped during crossing over
- however, errors during cell division alter chromosomes in daughter cells formed
- inversions, translocation, non disjunction
- gametes produced have faulty chromosomes or an incorrect chromosome number
sickle cell anaemia pop cause symptoms
Black african populations, India
mutation of the gene responsible for haemoglobin production
- sickle shape RBC, reduced oxygen carrying ability of RBC, fatigue, shortness of breath, anaemia, inflammation of hands and feet
sickle cell anaemia inheritance and effect on gene pool
recessive trait passed on from 2 carrier parents
homozygous : die from anaemia or malaria
heterozygous : have sickle trait, resistance to malaria, increase sickle cell allele freq. of population
tay-sachs pop cause symptoms
Ashkenazi Jews, Cajun people
missing enzyme essential for fat metabolism
fatty tissue in nervous system, mental and physical disabilities like cannot swallow, paralytic, blind, deaf
tay-sachs inheritance and effect on gene pool
homozygous: die because of Tay-sachs or TB
heterozygous: resistant to TB, increase tay-sachs allele freq. in population
