chapter 21 and 22 Flashcards
microevolution
change in allele frequencies over generations– 3 mechanisms ; natural selection, genetic drift, gene flow
genetic variation
individuals differ in inherited traits - selection acts on differences– mendel= mode of inheritance. - phenotypic variations reflects genetic variation.
-heritable variations occur on either or basis– single gene locus with multiple alleles that have distinct phenotypes or other phenotypic differences created from different alleles acting together (hair colour in humans)
genetic differences measured- in average percent of loci that are heterozygous
- nucleotide variability- doesn’t change phenotype if it occurs in introns
sources of genetic variation
mutation or gene duplication can create new allele and genes- if reproduction is fast variation an change rapidly
**sexual reproduction
new alleles
- can arise through mutations in gametes which are passed to offspring -most mutations in animals are in somatic cells
point mutation- one nucleotide and it can impact the phenotype (usually don’t do anything
-since phenotypes tend to match environment it is unlikely that a new mutation will improve
altering gene # or position
CHROMOSOME CHANGES-usually harmful but can rarely be good= mutations can accumulate and expand the genome -and give new functions
rapid reproduction
mutation rate is low but many mutations accumulate after many generations such as viruses
sexual reproduction
genetic variation from unique combination of alleles from each parent shuffles allies through meiosis and crossing over
population
group of individuals of same species - same area that interbreed and produce fertile offspring
gene pool
all copies of every type of alley at every locus in all members of population
fixed allele
only one allele that exists for a locus - all individuals homozygous
hardy weinberg equation
each allele has a frequency (proportion in population) hardy weinberg can determine genetic population if evolution is not occurring at a specific locus and compare it with the data observed - no difference between the two- the population is not evolving
principle- frequency of alleles / genotype in population will remain constant from gen to gen if only mendelian segregation and recombination of alleles are at work
equation pxp + 2pq +qxq = 1 and p + q = 1
conditions for hardy weinberg equilibrium
1 no mutations 2random mating 3no natural selection 4extremely large population 5no gene flow if these conditions are not met evolutionary change will occur and it is possible that specific genes can be in the hardy weinberg equilibrium
natural selection
different success in mating/ survival is due to better traits that are suited to the particular environment
genetic terms-alleles passed to next gene in proportions that differ from those present in the first one- allele frequency can rise if allele is beneficial
- certain alleles are favoured– ADAPTIVE EVOLUTION- evolution that results in batter match between organisms and their environment
genetic drift
chance events cause allele frequencies to fluctuate *** especially in small populations – founder effect and bottle neck effect
founder effect- individuals become isolated from a larger population and the new population has a differing gene pool this can account for high frequency of inherited diseases amongst isolated human populations
bottleneck effect- drop in population size due to sudden environmental changes- even if population can recover the frequency of alleles can still be altered. humans can cause severe bottlenecks
** can cause harmful alleles to become fixed
case study genetic drift and prairie chicken
praire to farmland which resulted in population drop of the prairie chicken the few that survived had little genetic variety , this was known as a bottleneck there was a loss of variation and increase in harmful alleles. when compared the prairie chickens lost 9 alleles.
gene flow
transfer of alleles into and out of the population due to movement of fertile individuals or gametes - this reduces genetic differences amongst populations ( two populations could even combine)
- alleles transferred by gene flow can affect how well populations adapt to local environmental conditions – gene flow is mating with other populations.
natural selection in depth
natural selection not random and favours some alleles over others adaptive evolution.
-relative fitness- certain traits in populations lead to greater relative fitness which is the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals - selection acts more on phenotype then genotype– the whole organism is up to selection
types of selection
( depends on phenotypes favoured)
- direction selection-codntions favour individuals at ONE extreme end of a phenotypic range shifting the populations frequency curve in one direction and it is common in environmental changes or migration
- disruptive selection-conditions favour individuals at both extremes of the phenotypic range
- stabilizing selection-acts against both extremes favours intermediate variants and it reduces variation
role of natural selection
adaptive evolution is a continuous dynamic process- natural selection is the only evolutionary mechanism that constantly leads to adaptive evolution
sexual selection
form of natural selection - individuals with certain inherited characteristics are more likely than other individuals to obtain mates and this sometimes results in *dimorphism- differences in secondary sexual characteristics between males and females of the same species.
intrasexual selection- selection within the same sex-compete for mates of the opposite sex, this is known as mate choice. one sex is choosy in selecting mates
preservation of genetic variation
neutral variation- differences in DNA that do not confer a selective advantage or disadvantage - directional and stabilizing selection reduce allele variation and diploidy and balancing selection restores it
- diploidy- genetic variation hid- recessive alleles if they are less favourable they survive within heterozygotes - if environment changes they may become more common.
- balancing selection- natural selection maintains two or more forms in a population and may preserve variations at some loci– heterozygous advantage and frequency dependant selection ?
heterozygous advantage
heterozygous at locus have greater fitness- in this case natural selection maintains two or more alleles at one locus in this case its genotype over phenotype- it could be any type of selection just depends on relationship between genotype and phenotype- ex of this is sickle cell in africa.
frequency dependant selection
fitness of phenotype depends on how common it is in a population ex two different alleles can oscillate depending on environmental conditions such as prey
why can’t natural selection make perfect organisms
1 selection can only act on existing variations- only favours traits actually in population
2evolution is limited by historical constraints it can only work on existing structures
3 adaptations are often compromises- colour attracts mates and predators
4chance, natural selection and environment interact
natural selection works on a better than basis ( not perfect)
microevolution
change in allele frequency of a population over many generations and these are caused by natural selection, genetic drift and gene flow LOOK AT HARDY WEINGBERG PRINCIPLE WORK SHEETS
macroevolution
broad scale evolution
biological species concept
species group of organisms who have potential to interbreed and produce fertile viable offspring
reproductive isolation
existence of biological berries that don’t allow members of a species to interbreed barriers bock gene flow r
**reproductive berries -habitat isolation-temporal isolation - bread at different times-behavioural isolation- mating and behavioural rituals– mate can’t recognize its mate mechanical isolation- morphological differences precent mating -gametic isolation-sperm can’t fertilize egg
pre zygotic barriers
block fertilization 1 members can’t meet
2attempted mate not completed hindering fertilization
3. development error?
post zygotic barriers
reduced hybrid viability- the development of the hybrid are impaired
reduced hybrid fertility- hybrids are sterile
hybrid breakdown- first hybrid get good but the second is impaired or sterile
limitations of biological species concept
its good because it shows speciation from reproductive isolation
its and because theres no way to evaluate reproductive isolate from fossils and it does not apply to organisms that do not reproduce sexually
species morphologically and ecologically disntict gene flow still occurs – ex grizzly and polar bear
increase in gene flow decrease in natural selection
morphological species concept
characterizes species according to body and structure - asexual and sexual organisms included. useful when gene flow unknown, bad- subjective criteria disagree on what features distinguish a species
phylogenetic species concept
smaller group of individuals that shares common ancestor (one branch ) compare morphology and DNA the bad part is how much can DNA differ of a species before you consider them different species.
ecological species concept
species in terms of ecological niche(interaction with environment)
allopatric speciation + process of allopatric speciation + evidence
-gene flow interrupted when population divided into geographically isolated subpopulations
-size of barrier to cause specetion depends on the species
if geographic separation occurs then gene pools may diverge and different mutations may arise in the gene pools an d natural selection causes genetic dat that alter allele frequencies ending up resulting in reproductive isolation (the two species can no longer mate)
-regions that are isolated or highly subdivide by berries typically have more species than do the similar regions that lack such features. ex galapagos islands with all the finches
sympatric speciation
occurs in populations that live in the same area– gene flow reduced by polyploidy, habitat differentiation, and sexual selection (LESS COMMON THAN ALLOPATRIC SPECIATION)
- polyploidy-extra chromosomes- common in plants
- autoploidy-individual has more than two chromosome sets that are all derived from a single species in plants a failure of chromosomal division 2n turns to 4n (tetraploid)- these are reproductively isolated from the parent cell and they can fertilize themselves and mutations can occur and so on resulting in a 4n plant.
- habitat differentiation- genetic factors enable sub population to split a habitat or a resource not used by the parent population– new food source and natural selection can occur
- sexual selection- mate choice based on male breeding- such as colouration can be the main reproductive barrier that keep gene pool separate
hybrid zone
region in which members of different species meet and mate producing offspring with mixed ancestry
PATTERNS- some form as narrow bands that usually occur where the two species habitats meet
ALLELE FREQUENCY PATTERN-gene flow does not occur- hybrid species usually are impaired and have a low chance of successful reproduction and natural selection can limit gene flow – if hybrid zones do not become their own species there are three possibilities 1. reinforcement- reproductive barriers reinforced when hybrids are less fit then their parents and natural selection reinforces the pre zygotic barriers.2 fusion- barriers are weak gene flow may occur and the gene pools may become increasingly similar and this can reverse speculation the two hybrids may fuse into a single species 3.stability the hybrids continue to be produced and the hybrids sure and reproduce better offspring than parent species in certain habitats or years
time of speciation
how long it takes a new species to form- broad patterns from fossil record morphological data or DNA sequences
patterns of fossil record- appears that new species appear suddenly and some disappear
–punctuated equilibrium- periods of apparent stasis functioned by sudden change
speciation rates
punctuated pattern- speciation begins and can be completed rapidly and natural selection can produce extensive genetic changes in hybrid populations over a short period of time– divergence must occur first but a new species can be produced fast
time- divergence of a species to the time when speciation is complete carries a lot and can range from thousands to millions of years the average is 6.5 million– speciation begins only after gene flow between populations interrupted and the population must diverge genetically so they become reproductively isolated.
