genetic diversity and adaptation Flashcards
differences in organisms
-organisms of the same species have very similar genomes
-there will be differences between their DNA base sequence
size of differences between individuals of the same species
small differences
genetic variation
the small differences in DNA base sequences between individual organisms within a species population
genetic variation transferred
genetic variation is transferred from one generation to the next
result of Genetic variation is transferred from one generation to the next
genetic diversity within a species population
genetic diversity
number of different alleles of genes in a population
mutation results in
genetic diversity if new alleles and contributes to genetic diversity or size of the gene pool
effect of mutation
-new allele may be advantageous, disadvantageous or have no apparent effect phenotype (due to genetic code being degenerate)
-new alleles are not always seen in the individual that they first occur in
-they can remain hidden (not expressed) within a population for several generations before they contribute to phenotypic variation
what is needed for natural selection to occur
some level of genetic diversity within a population
differences in alleles possessed by individuals within a population results in
difference in phenotypes
environmental factors affect the chance of individuals within a specific phenotype surviving and reproducing over others acts as a
selection pressure
individuals described as having a higher fitness have
favored phenotype
fitness of an organism
-defined as its ability to survive and pass on its alleles to offspring
-organisms with higher fitness posses adaptations that make them better suited to their environment
population with a large gene pool or high genetic diversity
has a string ability to adapt to change
population has a small gene pool or very low genetic diversity
much less able to adapt to changes in the environment and so become vulnerable to extinction
cheetahs as an example of having a small gene pool
-cheetahs are an example of a species with an extremely small gene pool
-they experienced a very large decline in numbers approximately 10,000 years ago
-this left small, fragmented populations of individuals remaining
-there was no mixing between population and large amounts of inbreeding occurred
-this is problematic for conservation as low genetic variation means the species are less likely to be able to respond (survive) in the event if any environmental changes
bacteria colonies growth
can grow at rapid rates when in culture with very large numbers of bacteria produced within long hours
why is dealing with experimental data relating to large numbers of bacteria difficult using traditional linear scales
-there is a wide range of very small and very large numbers
-this makes it hard to work out a suitable scale for the axes of graphs
useful scales when investigating bacteria
logarithmic scales
logarithmic scales allow for
a wide range if values to be displayed on a single graph
example of logarithmic graph using yeast cells
-yeast cells were grown in culture over several hours. the number of cells increased very rapidly form original number of yeast cells present
-can be shown on a log scale
-the number of yeast cells present at each time interval was converted to a logarithm before being plotted on the graph
-the log scale is easily identifiable as there are no equal intervals between numbers on the y-axis
-the wide range of cell numbers fit easily onto the same scale
why is pH scale logarithmic
concentration of hydrogen ions varies massively between each pH level
why does genetic variation exist within populations
presence of different alleles
where is there different reproductive success
between organisms with different alleles of the same gene
reproductive success
number of offspring an individual produces (per breeding event or in their lifetime)
when will individuals with certain alleles have an increased chance of survival and reproduction
under certain environmental conditions
how can new alleles arise on populations
random mutation
natural selection can cause
the frequency of alleles in a population to change overtime
principles of natural selection
-random mutation can produce new alleles of a gene
-many mutations are harmful or neutral but, under certain environmental conditions, the new alleles may benefit their possessor, leading to an increased reproductive success
-this advantageous allele is passed onto the next generation
-as a result, over several generations, the new allele will increase in frequency in the population
example of natural selection in rabbits
-variation in fur colour exists within rabbit populations
-at a single gene locus, normal brown fur is produced by a dominant allele whereas white fur is produced by a recessive allele in a homozygous individual
-rabbits have natural predators like foxes which act as selection pressure
-rabbits with a white coat do not camouflage as well as rabbits with brown fur, meaning predators are more likely to see rabbits with brown fur
-therefore, the rabbits with brown fir have a selection advantage, so they are more likely to survive to a reproductive age and be able to pass on their alleles to their offspring
-over many generations, the frequency of alleles for brown fur will increase and the frequency of alleles of white fur will decrease
what does natural selection cause
a change in allele frequencies over time
why does Natural selection causes a change in allele frequencies over time
selection pressures (caused by the environment an organism is in) increase the likelihood that certain individuals with specific alleles survive to reproductive age, enabling them to pass alleles to their offspring
natural selection
Darwin’s theory to explain the mechanism of evolution. the processes by which organisms better adapted to their environment survive and reproduce and pass on their advantageous alleles to their offspring, whilst those less well adapted fail to do so
other factors or processes that can effect allele frequencies in a population
-founder effect
-genetic drift
-the bottleneck effect
the founder effect
-occurs when only a small number of individuals from a large parent population start a new population
-as the new population is made of only a few individuals from the original population only some of the total alleles from the parent population will be present
-so not all the gene pool is present in the smaller population –> a gene pool is the complete range of DNA sequences (allele) that exist in all the individuals of a population or species
-which alleles end up in the new founding population is completely up to chance
-as a result, the changes in allele frequencies may occur in a different direction for the new small population vs the larger parent population
the founder effect in lizards
-anole lizards inhibit mist Caribbean islands and they can travel from one island to another via floating debris or vegetation
-the individual lizards that arrive on the island, as well as they alleles they carry is due to chance
-they may only carry a small selection of alleles, with many more alleles present in the lizard population on the original island
-the lizards on the island could display a range of scale colours from white to yellow and the two individual lizards that arrived on the island might only have individuals with white scales
-this means hat the whole population that grows on that island might only have individuals with white scales
-In comparison, the original island population has a mixture of white and yellow scaled individuals. This difference between the two populations is completely due to chance
genetic drift
-when a population is significantly small, chance can affect which alleles get passed onto the next generation
-over time some alleles can be lost of favoured purely by chance
-when there is a gradual change in allele frequency in a small population due to chance and not natural selection then genetic drift is occurring
example of genetic drift in plants
-in a small population of 5 plants growing near a playground with rubber floor: 3 of the plants have pink and white flowers
-by chance, most of the seeds from the pink-and-white flowered plants end up on the rubber floor of the playground, whereas all the seeds from the blue-and-white flowered plants land on fresh fertile soil where they are able to germinate and grow
-Over several generations, the allele for the pink-and-white flowers may disappear from this population due to chance (because the seeds carrying pink-and-white alleles for flower colour cannot germinate on rubber)
bottleneck effect
-similar to the founder effect
-it occurs when a previously large population suffers a dramatic fall in numbers
-a major environmental event can massively reduce the number of individuals in a population which in turn reduced the genetic diversity in the population as alleles are lost
-the supervising individuals end up breeding and reproducing with close relatives
example of the bottleneck effect
A clear example of a genetic bottleneck can be seen in cheetahs today
Roughly 10,000 years ago there was a large and genetically diverse cheetah population
Most of the population was suddenly killed off when the climate changed drastically at the end of the Ice Age
As a result, the surviving cheetahs were isolated in small populations and lots of inbreeding occurred
This meant that the cheetah population today has a serious lack of genetic variation
This is problematic for conservation as genetic variation within a species increases the likelihood that the species is able to respond (survive) in the event of any environmental changes
Remember the environment exerts a selection pressure on organisms
selection pressures
environmental factors that affect the chance of survival of an organism are selection pressures
example of selection pressures
there could be high competition for food between lions if there is not plentiful prey available, this environmental factor selects faster, more powerful lions that are better hunters
effects of selection pressures
the allele frequencies of a population through natural selection
types of selection
-stabilising
-directional
stabilising selection
natural selection that keeps allele frequencies relatively constant over generations
what does stabilising selection means
things stay as they are unless there is a change in the environment
example of stalibilsing selections in human birth rates
very-low and very-high birth weights are selected against leading to the maintenance of the intermediate birth weights
directional selection
natural selection that produces a gradual change in allele frequency over several generations
when does gradual selection usually occur
when there is a change in environment/selection pressures or a new allele has appeared in the population that is advantageous
example of directional selection in antibiotic resistant bacteria strains are becoming more common due to overuse of antibiotics
-the presence if antibiotics is a selection pressure
-mutations are becoming in bacteria populations randomly
-a mutation arises that confers antibiotic resistance - it has a beneficial allele
-bacteria with this mutation are more likely to survive and reproduce
-most bacteria with this mutation are more likely to survive and reproduce
-most bacteria without the resistance mutation die
-over generations, this leads to an increase in the frequency of beneficial allele that produces antibiotic resistance
affect of selection pressures on allele frequencies
have different effects on allele frequencies of a population through natural selection
adaptations
certain alleles within a species population can produce features that make an organism better suited to its environment
when is there potential for relatively rapid changes in a species
when new alleles of genes reult form mutations there is the potential for relatively rapid change in a species if their environement changes
example of favourable allele in lion population
a higher proportion of fast-twitch muscle fibres in their legs, which is advantageous for sprinting after prey
natural selection will select
favourable alleles that produce adaptations
what will natural selection select against
unfavourable alleles
over time natural selection will cause
favourable allele frequencies to increase and unfoavourable allele frequencies to decrease, making the sapecies better adapted for the environment
3 types of adaptations
-anatomical adaptations
-physiological adaptations
-behavioral adaptations
anatomical adaptations
-structural/physical feature
-for example the white fur of polar bears provides camouflage in the snow so it has less chance of being detected by prey
physiological adaptations
-biological processes within the organisms
-for example mosquito’s produce chemicals that stop the animal’s blood clotting when they bite, so they can feed more easily
behavioural adaptations
-the way an organism behaves
-for example cold-blooded reptiles bask in the sun to absorb heat
2 major factors in the process of evolution
adaptation and selection
evolution
change in adaptive features of a population over time as a result of natural selection
evolution in a static environment
will not occur as selection pressures will not change
effect of environmental changes or chance mutations on selection pressures
may favour individuals with different characteristics or with the new allele
what processes does natural selection result in
adaptation. which means that over generations, those features that are better adapted to the environment became more common, this means whole populations of organisms become better suited to the environment
what happens if two species are isolated from each other
they may become so different in phenotype that they can no longer interbreed to produce fertile offspring, they have formed 2 new species
what is formation of new species from pre-existing species over time a result of
accumulated genetic differences
what is evolution responsible for
large number of species that exist on earth as drives speciation
practical of affecting microbial growth- important techniques used
aseptic techniques
why are aseptic techniques used
ensure microbes being investigated don’t escape or become contaminated with another unwanted, and possibly pathogenic microbe
examples of aseptic techniques
-disinfecting work surfaces with disinfectant/alcohol
-not allowing growth if microorganisms at body temperature
-using famed loops or sterile swabs when transferring cultures
-wearing gloves and googles
-flaming culture bottlenecks to prevent contamination
-having a lit Bunsen burner in the room
-only removing perti dish lids when necessary
