variation Flashcards
sources of variation
random mutations
crossing over during meiosis
independent assortment of chromosomes @ meiosis 1
independent assortment of chromosomes @ meiosis 2
random fertilisation of gametes
benefits of variation
beneficial to survive in a changing environment
which variation can be inherited
info on gametes genotypes epigenetic changes (sometimes)
which generation cannot be inherited
epigenetic changes (most ) environmental variation
what is bacteria resistant to and why
penicillin
selection pressure is a change in the environment that causes some alleles to be chosen above others
what happens if the environment changes
over production =
more offspring are produced than survive. many die without reproducing
define interspecific
competition between other species
e.g. space, water, food, sunlight
define intra-specific
competition between the same species
e.g. space, water, food, sunlight, mates
VARIATION IS ABOUT BEING BETTER AT COMPETING FOR LIMITED RESOURCES
examples of selection pressures
food mates predation pollution temperature
why is selection pressure goof
allows the fittest to survive, reproduce and pass on alleles
what are the two types of variation
continuous
discontinuous
what factors are in continuous variation
gradation, many genes e.g. height
what factors are in discontinuous variation
clear cut, single gene, e.g. blood group
what are the two origins of variation
non-heritable = environmental heritable = genetic changes
examples of non-heritable variation
diet, exercise, temp, light
examples of heritable variation
mutations, meoisis, fertilisation
define population
a group of organisms that can interbreed
define open
overlapping population = immigration of alleles
define closed
barriers between population
define gene pool
total of available alleles in reproductive cells
define allele frequency
relative proportion of alleles (which in turn determines the proportions of genotypes)
why would a gene pool change
mutations
genetic drift
disasters resulting in the loss of a section of population
natural selection - unable to compete
characteristics of continuous variation
no distinct categories
quantitative
controlled by a lot of genes
strongly influences by environment
characteristics of discontinuous variation
distinctive categories
tends to be qualitative
controlled by a few genes
unaffected by environment
what do we use to determine differences between discrete data
chi squared
what do we use to determine differences between continuous data
students T test
what is a T test
can tell you if there is a statistically significant difference between 2 means when :
sample is less than 25
data is normally distributed
how do you work out degree of freedom
N1+N2-2
define allele frequency
the frequency of an allele is its proportion, fraction or % of all the allele of that gene in a gene pool
define genetic drift
chance variation in allel frequencies in a population, change in the frequency of an allele in as population due to random sampling of organisms
what can you use hardy weinberg for
allows us to detect change or constancy in gene pools. discovered by two scientists who were trying to work out why dominant alleles don’t take over in populations
what happens if there is over a million individuals
if there are a million individuals then 10,000 individuals possess the allele. if mating is random with respect to allele then the frequency of the next generation will stay the same
what happens is the population is much smaller
only 10 will carry the allele, if by chance, one of ten fails to reproduce and pass on the allele its frequency in the next generation is reduceed by 10%
what happens in a small population
it may be that none of those possessing the allele mate. then the allele is lost altogether
ideal conditions of Hardy Weinberg
the organisms ->
- diploid
- allele frequencies are equal in both sexes
- the reproduce sexually
- mating is random
- generations do not overlap
the population ->
- size is large
- no migration
- no mutation
- no selection
what are the 2 hardy weinberg equations
p+q=1
p^2+2pq+q^2=1
define species
a group of organisms that interbreed to produce fertile offspring
what does Hardy Weinberg assume
the allele frequencies do not change over time
what is the reality of the allele frequencies
do change accompanied by a change in the phenotype of the population
eventually individuals become different enough from the original population to be unable to breed with it. at this point they are said to be different species
what are the three types of natural selection
directional selection
disruptive election
stabilising selection
define directional selection
acts against one of the extremes in a range on phenotypes. as a result one phenotype becomes rare and an alternative phenotype becomes more common e.g. giraffe necks
natural selection has caused a genetic change in this population, favouring organisms with a characteristic towards the upper range of the frequency distribution
define stabilising selection
e.g. birth weight in babies –> low weight babies have health issues and high weight babies have complications so both are less likely to survive. the mean weight are most likely to survive
the average phenotype may provide greater advantage than the extreme.
the extreme values are selected against.
in future generations the average stays the same but more individuals have the same value
define disruptive selection
eg shell colours in limpets. light colour shells blend in with barnacle covered rocks, dark coloured shells blend in with bare rock. medium coloured shells stand out on both rocks
average phenotype does not provide an advantage and is elected against. the most extreme phenotypes are the most advantageous. a bimodal curve is produced.
what changes the average phenotype
both directional and disruptive selection change the average phenotype.
what is pre zygotic isolation
gametes are prevented from fusing so a zygote is never formed
what is post zygotic isolation
gametes fuse and zygotes forms. both sterile
define geographical isolation
allopatric speciation
refers to geographical isolation to produce new species
eg land mass seperation, mountain ranges, rivers, lakes drying up into smaller lakes
what is behavioural isolation
sympatric speciation
mating rituals and courtship displays that are recognised by other members of the species as a prelude the mating
if individuals of a species living in the same location as the main population undergo variation, there may prevent them from mating with other members of the population
over time they will only breed with others that show the variation and will gradually become different from the main population
be different enough to be a new species
what is morphological isolation
sympatric speciation
change in the body of species which causes a reproductive barrier so that genes cannot mix. the individuals that are reproductively isolated share a habitat so speciation resulting from morphological isolation is sympatric
what is gametic isolation
gametes in open environments often meet gametes of other species
in 1/3 of cases they make viable interspecies hybrids, an important feature in coral evolution but 2/3 are incompatible
barriers prevent the fusion of gametes of different species, so populations are isolated :
- there are molecules in gamete membranes that prevent interspecies fusion
- chemo-attractants secreted by female gametes are only recognised by male gametes of the same species
- the pollen of many angiosperm can germinate on the stigma of another species but the pollen tube only penetrates a small distance down the style and does not reach the ovule
- the sperm of many animals does not survive in the oviduct of other species
what is seasonal isolation
sympatric speciation
reproductive organs of different demes are mature at different times of the year. therefore unable to hybridise and are genetically isolated.
eg buttercup and less celandine
what is hybrid inviability
fertilisation occurs but incompatibility between the genes of the parents prevents the development of an embryo
e.g. northern leopard from and wood frog
what is hybrid sterility
sympatric speciation
an embryo formed from the gametes of two species can develop
if chromosomes are not sufficiently similar they are unable to pair at prophase 1 of meiosis so gametes cannot form - this means the hybrid is sterile, this prevents gene flow so species remain distinct
eg mule - female donkey and male horse
what is hybrid breakdown
some F1 hybrids are fertile but their F2 is sterile. this is more common in plants than in animals and is best known in cotton, legumes and rice.
incompatibility between nuclear genes and genes in mitochondria and chloroplasts have explained some cases of this
what is adaptive radiation
process in which organisms diversify rapidly from an ancestral species into a multitude of new forms e.g. the finch and the pentadactyl limb
what is molecular evidence
studying the genetic code/protein synthesis in organisms
has shown that all life evolved from a single common ancestor
provides a record of genetic change over time
what is DNA hybridisation
a single strand of DNA from one species is mixed with a single strand from another species. the more similar the DNA is, the more of the base pairs will match up
used to prove the similarities between organisms
supports darwins out of africa hypothesis - that humans evolved from apes in africa
what is DNA profiling/ genetic fingerprinting
used to study mutations as the enzymes will cut the base sequences differently if the sequence had changed
provides evidence of genetic differences between species
what is DNA and protein sequencing
comparing the base sequences of DNA or amino acids in different species
has proven which organisms have evolved from a common ancestor and how recently
what is proteomics
the study of proteins, their structure and their function
the exact amino acids sequences of the same protein (insulin) will vary from species to species
the more closely related species are in their evaluation the more similarities we expect to see in their amino acids sequences of their proteins
what is DNA molecular clocks
uses PCR and automated DNA sequencing mechanisms to allow rapid determination of the DNA base sequences
used to compare the number of differences between species to calculate how long ago they shared a common ancestor
used to construct evolutionary trees which support Darwin’s theory of evolution over a vast time period
what did Darwin deduce
there is a struggle for extreme with only the fittest surviving
those that survive reproduce and their offspring have the characteristics that enable them to succeed
if environmental conditions change, the features needed to survive in it will change so natural selection is a continuous process
