changes in allele frequencies in gene pools

changes to allele frequencies in gene pools can be due to…

gene flow between populations, random genetic drift including the founder effect and the bottleneck effect and natural selection.

what is gene flow?

it is the movement of genetic material from one population to another.

what enables gene flow?

when people move between populations, immigrants bring in alleles that are not already in the population and therefore altering the frequencies of alleles.

give an example of genetic drift due to migration. (RH factor)

in the past all Chinese population was the RH (Rhesus factor) positive blood group. But when European countries began trading with china in the 16th century. The European immigrants/ sailors introduced RH- allele into the population.
(frequency of RH- allele is still relatively low today)

what is the Rhesus facotor from blood cells?

it is the antigen found the surface of Red blood cells. People who have the antigen are RH+ and people who dont are RH-

give an example of genetic drift from migration (ABO blood groups)

there was a change in frequency of the I B allele across Europe and Asia. In east Asia there was a high frequency of allele of I B than those in the west of Europe. Throughout history most of Western Europe did not have the I B allele at all but in the 12th and 13th century the Mongols (from east Asia) invaded Europe on a number of occasions, spreading their culture and their genes. Today there is a steady decrease in the I B allele from Central Asia to Western Europe. Now there is a decrease in concentration of the I B allele in the Pyrenees mountains in isolated locations in Scandinavia.

isolations of populations leads to…

seperate gene pools forming

when there are barriers to gene flow what happens to the rate of interbreeding?

the rate of interbreeding decreases and will lead to seperate gene pools forming.

what are the barriers to gene flow?

there are geographical and socio- cultural barriers

what are the geographical barriers to gene flow?

oceans, mountain rangers, large lake systems, deserts, ice sheets. The isolation over time means that different gene pools develop. Natural selection means that advantageous traits for the environment are more common. For example Aboriginal Australians were isolated for thousands of years are the sea levels rose.

what are the socio- cultural barriers to gene flow?

economic status, education background, social position. Stats indicate that Australians tend to marry people of similar education background and members of the same religion. Language barriers can interfere with interbreeding and in the past cousin marriage in the Mediterranean to preserve property and power (cultural isolation)

what are the disadvantages to barriers to gene flow?

there is a greater incidence of genetic disease; in a small isolated population there would be marriage between close relatives e.g cousins- this means two carriers for a disease are more likely to marry and therfore there is a greater incidence of disease. And that advantageous genes won’t enter the population through migration.

what are the advantages to barriers to gene flow?

that lethal recessive alleles from other populations are less likely to enter the isolated population

what are the other names for genetic drift?

random genetic drift or the Sewall Wright effect

what is genetic drift?

in a generation there is always a chance that some individuals will be more, or less likely to pass on their allele. This is random and non- directional. The allele frequency change is by chance and is not effected if an allele is beneficial or harmful it is purely by chance.

what size population does genetic drift effect?

it occurs in populations of all sizes however it is less likely to have a significant effect in large populations.

Genetic drift can play an important role in…

evolution in small populations

who is Sewall Wright?

is the man who recognised genetics drifts significance in causing changes to allele frequencies.

why is genetic drift random?

the allele frequencies changes are due to random/ chance factors for example the subset of the population becoming isolated, migration and interbreeding, and more people with a particular allele having more children through random chance.

Is genetic drift an advantage or a disadvantage?

it is neither as it is a random process

what is the analogy used to describe genetic drift?

if you have a container with 50 Black counters and 50 red counters, and you pick a random sample of 20 red and 30 black. They all reproduce to 40 red to 60 black. Then you take another sample of that sample and get 15 red and 35 black. if they all reproduce again and you would now have 30 red and 70 black. You would expect that black to be favoured in the population

why is genetic drift non- directional?

the frequency of a particular allele can increase or decrease over time due to random factors.

Give an example to explain how genetic drift is unidirectional.

red hair. for example red- haired people might randomly have kids one generation and increase the allele frequency of red hair. But the next generation might have a decreased frequency of people with red hair, decreasing the allele frequency, the next generation gayer that might be more.

explain how genetic drift is non-adaptive and not influenced but the environment.

the change in allele frequency dos not cause and adaptive advantage for the environment. It does cause an increase in change of survival or reproduction. For example, the increase in allele frequency for straight hair causes no advantage.

link genetic drift to Aboriginal Australians.

the populations of Bentinck and Mornington islands in the Gulf of Carpentaria. the rising sea levels cut this population off from the mainland and therefore the populations became isolated. It was found that the occupants of Bentinck island show allele frequency values for blood groups that fall outside the range for Aboriginal people on the rest of Australia. They show an increased proportion of the I B allele and the absence of I A allele (blood groups). the mainland population have a low proportion of I B allele and relatively high proportion of I A allele.

explain how the “dunkers” indicate evidence for genetic drift.

dunkers are USA religious group similar to the Amish originally from Germany coming to America approx 300 years ago. these people marry and reproduce only within the community. therefore the dunkers have different allele frequencies to modern day germans from Hesse and the surrounding American community. this has to be random genetic drift as it is not random selection as they have the same environment.

the dunkers are an example of the…

founder effect, this is because their religion does not allow them to marry outside their group, and therfore they constitute an isolated breeding population within the total population of USA

what is the founder effect?

it occurs when a small group moves away from its homeland to a totally new area and establishes a population, which later expands, as this isolated population expands so does the allele frequency. Because of the small size, chance can cause the new groups to have; different allele frequency from the original population and a decreased genetic variation.

because of the small size of the new population in the founder effect what happens?

there is a chance that the new groups to have; a different allele frequency from the original population and a decreased genetic variation. meaning the new population may show a frequency of features that are not typical of the original homeland population

what has been studied to change from the founder effect?

ABO, Rh, MN blood group, mid digit hair, left/ right handedness, detached or free earlobes. These certain characteristics are more common purely by chance

give an example of the founder effect, link to Tay Sachs disease

within the community of Ashkenazi Jews pro 1 in 27 carries the altered allele- in comparison to the 1 in 300 non- Ashkenazi jews. This group is isolated geographically, and on top of that there is additional isolation through the custom of endogamy (only marrying within the community). The incidence for the mutated allele for Tay Sachs disease was high in ancestors, and hence genetic drift is responsible for the prevalence of the disease in the current population.

what is the bottleneck effect?

is an extreme example of genetic drift. For example a natural disaster severally reduced the size of the population. The allele frequency after the disaster may, by chance be different than before the event

is the bottleneck effect due to a specific trait?

no, chance of survival is by chance and is not due to a specific trait . as the population expands, so does the new allele frequency

Give an example of the bottleneck effect?

in 1775 a typhoon decreased the population size of pingelap to only 20. within these survivors one person carried the recessive allele for achromatopsia (total colour blindness). After a number of generations achromatopsia on pingelap is 5% of the population, whereas in the rest of the world is 0.0033% (and 30 of pingelap population are carriers).

natural selection is the explanation of…

the huge diversity of life on earth.

when was natural selection first put forward?

in 1858 by Charles Darwin and Alfred Russel Wallace

who was Charles Darwin?

a keen amateur naturalist, as a young man joined a surveying expedition as its biologist- he voyaged on the HMS Beagle, visiting (among others) the Galápagos Islands, New Zealand and Australia. the materials he collected was the preparation for all his later work.

while Charles Darwin was o his expedition on these islands, what find?

he became convinces that species did change.

Darwin was able to observe differences and similarities by what?

geography—> those living on the mainland of South America and those on various islands

time—> animals recently extinct and those who are still alive.

what were the different scientists influenced Dawins work?

Carlus Linnaeus, Charles Lyell, Alfred Russel Wallace and Thomas Malthus

what was Carols Linnaeus’s work?

he established the basis of our current system of classification and the binomial system of naming. Using the genetic (genus) and the specific (species) names this allowed Darwin to classify and organise data he collected .

what was Charles Lyell?

he published a book ‘the principles of Geology’ Lyell hypothesised that the natural forces existing in the past were much the same as those existing in his own time. hypothesis implied the earths surface had been gradually moulded over a very long period of time, by simple forces such as changes in temperature, running water, earths movements. These ideas provided Darwin with the idea of constant change against he could via his work.

what was Thomas Malthus work ?

he provided idea for theory of natural selection. ‘An essay on the principle of population’ pointed out that the human population is increasing a a rate far exceeding the rate of food production. Natural reproduction rate exceeded the available resources (more plants and animal reproduce than can possibly survive

what was Alfred Russel Wallaces work?

wrote an essay ‘on the tendency if varieties to depend indefinitely from the original type. This influenced Darwin to publish his ideas, a joint essay by Wallace and Darwin in 1858, years later Darwin published book ‘On the origin go species’

after Malthus theory, what did Darwin hypothesise?

Malthus theory that natural reproduction rate exceeded natural resources Darwin realised that under these circumstances a struggle for existence would occur. excessive birth rate and limited resources

what is special creation?

it used to be widely believed that God, or a supreme being had individually created each species

what were the three observations that built up Darwins theory of natural selection

variation, birth rate and natures balance

what is variation in regards to natural selection?

Darwin noted all members of a species (did not attempt to explain), however did point out that these variations were passed on to one generation to the next, with characteristics displayed by parents being passed on to offspring

what is birth rate in regards to natural selection?

inspired by Malthus, Darwin realised that all living organisms reproduce at a rate far greater than that at which their food supply and other resources increase. This would result in overcrowding

what is natures balance to natural section?

Darwin observed that, although the birth rate of organisms was very high, each species numbers trended to remain at a relatively constant rate.

what conclusion did Darwin come to after realising the excessive birth rate and limited resources?

there must be a struggle for existence and second, therefore there was a range in variations in any species. Those with characteristics best suited to their environment were more likely to survive, Survival for existence

what is survival of the fittest?

organising with favourable characteristics survive, organisms with less favourable characteristics die before they can reproduce and therfore pass on the trait.

survival of the fittest is possible because of…

variation, the members of a species differ from one another in their physical characteristics, body function and behaviour

with further research what answered the flaws in the natural selection

knowledge of mechanisms of inheritance, events of meiosis/ fertilisation, inheritance of alleles from mother and father for alternate forms of a trait or characteristic, chance mutations

how is natural selection defined by today?

the selection of those alleles in the population that give an organism a greater survival advantage. Favourable alleles passed to offspring so it becomes better suited to its environment, change in gene pool over time adaption of the species to the gradually changing environment. the characteristics that enhance survival enable succeeding generations to gradually adapt to it .

do individual organisms adapt…

no, the species as a whole adapts to its environment by natural selection (takes many generations)

explain natural selection in terms of the frequencies of alleles in the gene pool of a population?

if the environment tends o favour a particular characteristic, more of the alleles for that trait will be passed on to the next generation. Resulting in a change in the frequency of that allele in the gene pool. therefore over time that characteristic becomes more frequent in the population.

state the principles of evolution through natural selection summarised.

there is variation of characteristics within a species, more offspring of a species are produced that can possibly survive maturity, because of excessive birth rate and limited resources, there is a struggle for existence or competition for survival, individuals with characteristics best suited to the environment have more chance of surviving and reproducing- this is known as survival of the fittest, Favourable characteristics are passed don to the next generation, in the gene pool, the proportion of alleles that produce favourable characteristics gradually increases.

explain how natural selection is not a random process.

the allele frequency changes due to environmental factors, making some alleles more favourable for the reproduction/ survival in a particular environment

give an example to how natural selection is not a random process.

the allele for longer coat length is an advantage I cold climates as the animal doesn’t have to expend as much energy to stay warm. animals expressing this allele are more likely to maintain body temp to survive and/ or reproduce more offspring, so the allele frequency would increase over time.

explain how natural selection is directional.

the frequency of an allele in the population os consistently increasing over time if it is an advantage and consistantly decreasing over time if its a disadvantage

explain how genetic drift is non- adaptive.

change in allele frequency doesn’t cause an advantage in the environment.

explain how natural selection its adaptive and influenced by environmental pressures.

change in allele frequency helps the species to adapt to its current environment. The change in allele frequency can clearly be related to environmental pressures applying pressure.

how can you tell if a change to allele frequency is the result of genetic drift or natural selection?

look at its directionality, if the gene frequency is consistently decreasing over several generations, it is likely to be because it provided some kid of advantage I the environmental conditions of the population. If the frequency fluctuates up and down over time, it is likely to be random drift

explain how natural selection has influenced body stature.

initially the human gene pool would have contained alleles for a whole range of statures. individuals with long bodies and short limbs have a smaller surface area in relation to body volume than those with short bodies and long limbs. Such individuals lose less heat in very cold environments and therefore would have. survival advantage. Therfore they would reproduce and pass on the favourable allele to their offspring (as fewer short body, long limbs would not survive the extreme cold) therefore would not survive to reproductive age and therfrire the frequency of unfavourable alleles in the gene pool gradually decrease

what is the body stature of the Inuit peoples?

long bodies and short limbs, they have a smaller SA in relation to body volume, therfore decreased heat loss and therefore are more adapted to colder conditions

what is the body stature of the Masai peoples?

they have an increased SA to body volume ratio and therfore have an increased heat loss and are adapted to warmer climates.

all humans have basic similarities and are capable..

of interbreeding to produce fertile offspring (this is because all humans belong to the same species)

what is a species?

is a group of individuals that share many characteristics and are able to interbreed under normal conditions to produce fertile offspring.

what happens if two populations are isolated in different environments for a very long time?

different alleles will be favoured, and therefore there would be major changes in allele frequencies within each population. In such situation, the members of those populations may become so different that, even if barriers to reproduction were removed, interbreeding would not be possible. if this occurred the two populations would be regarded as seperate species,

what is speciation?

is the process of producing two different species.

what separates two populations during speciation?

isolation is a barrier to gene flow, reproductive isolation may lead to the development of seperate gene pools, no twi environments are the same, so therfore it is expected that certain alleles would be favoured for survival. over many generations, the populations will become less and less alike as they develop characteristics to better suit them to their respective environments

what are the steps involved in speciation?

variation, isolation, selection, speciation

what is/ explain the first step in speciation.

variation, this is when a population exists on an island with a range of variations which shares a common gene pool.

what is/ explain the second step in speciation.

isolation, the species is divided into two populations by a barrier dividing the population into two. no interbreeding occurs between the two populations. each population has a seperate gene pool.

is a physical barrier needed for speciation?

no it is not always necessary for speciation. This can happen if a species is spread over a wide georgraphiocal location with different environmental pressures.

what is/ explain the third step in speciation.

selection, two subspecies begin to form, as different elective pressures act on each of these two populations over a number of generations. bringing a change in the gene frequencies of each gene pool, such changes lead to the evolution of a seperate species

what is the last/ fourth step of speciation/ explain it.

speciation, now two species exist, over a long period of time the changes in the gene frequencies may be great enough to prevent the production of future offspring by interbreeding between the two populations from ever occurring again.

what is heterozygote advantage?

it is when carrying one allele for a recessive genetic disease is an advantage in a particular environment. Carriers have a survival advantage, therefore allele frequency rises even though there is a disadvantage for homozygous recessive people who get the disease.

what are some examples of diseases which have a heterozygote advantage?

sickle cell anaemia, alpha thalessemia, Tay Sachs disease

what mosquito carries malaria

the anopheles mosquito, it transmits the malarial parasite

where are anopheles mosquitos usually found ?

they usually dont inhibit tropical forrests, thy need quite stagnant pools of water for breeding sites, most are found in open areas as humans began to clear the forrests of Africa for agriculture, they changed the environment in a manner that created additional breeding areas for the mosquitoes. Also an increased food supply from agricultural production allowed human population to increase, providing more bodies for mosquitoes to feed

when was sickle cell disease discovered?

in 1910. person had symptoms of clogged blood vessels, pheunonia, rheumatism, heart disease, inflammation of hands and for, anaemia. a doctor took a blood sample and observed it under a microscope and when air was excluded from sample. the red blood cells showed a sickle shape.

what causes the sickle cell anaemia?

a substitution point mutation in the DNA sequence of the HBB gene. this different base sequence means amino acid valine is added instead of glutamic acid. Therefore resulting in a different protein, which will distort the shape of the red blood cells

what does the HBB gene code for?

it codes for one of the beta-globulin proteins that make uo the haemoglobin in the red blood cells

what happens to your blood if a person is heterozygous for sickle cell anaemia?

only some of the blood cells are sickled as allele for normal blood haemoglobin is dominant, there are no symptoms, unless oxygen is in short supply (when this occurs, blood cells show mild sickling). they are a carrier for the allele and it can be passed on to offspring.

what are the symptoms of sickle cell disease?

sickle shaped red blood cells that often die early, resulting in anaemia, they are inflexible and become stuck in blood vessels, causing blockage, fatigue, jaundice, organ damage to the kidneys, lungs and brain, high blood pressure, and heart failure.

what happens if you have sickle cell disease?

you would have a faulty haemoglobin and the inability to adequately transport O2 and death in childhood.

what are the rates of sickle cell anaemia?

if a person dies before reproducing, the allele that causes disease is not passed on to the next generation. You would expect over many generations the frequency of sickle decrease until it is eliminated. however this is not the case studies show that the rate of alleles being lost from population is approx 100 times greater than average rate of mutation at ay point on the human chromosome. therefore there must be some other mechanism at work to maintain the sickle cell allele in the population. the sickle cell allele are only in areas where malaria is prevalent.

what did Anthony Alison find out?

that the sickling allele tended to have its highest frequency in areas where the risk from malarial parasites was greatest. Individuals with one sicllecell allele were more resistant to malaria than those with notmal haemoglobin in their red blood cells.

what is the selection pressure between sickle cell and malaria?

the presence of malaria acts as a selection pressure for the sickle cell allele (or acting as the selecting agent)

what is the heterozyote advantage of having sickle cell disease?

having one of the alleles for sickle cell disease, individuals living in malarial prone areas have a survival advantage.

who has the greatest advantage with the presence for the sickle cell allele in non malarial areas?

the greatest advantage is held by those with normal blood (no sickle cell allele) as they are most likely to survive and bear young.

who has the greatest advantage with the presence of sickle cell allele in malarial areas?

people with normal blood survive to bear young but some will die from malaria. People who have two alleles for sickle cell disease die at around 40 years. But people who carry one sickle allele survive from the sickle cell disease ad are able to not get malaria or recover faster. therefore they are at an advantage and the allele is passed on to a greater degree in areas with malaria

what is Thalassemia

is an autosomal recessive disease causing defects. of haemoglobin production.

what is thalassemia caused by?

base. insertion.

what is haemoglobin made up of?

4 protein chains that ft together. 2 for alpha globin chains and 2 for beta globin chains.

what are the two forms of Thalasemia?

alpha thalasemmia and beta thalasemia

what is alpha thalassemia caused by?

caused by a mutation in the HBA gene on chromosome 16. this reduces the amount of alphaglobin in haemoglobin

what is beta thalassemia caused by?

caused by a mutation in the HBB gene on chromosome 11