4B Diversity, Classification and Variation Flashcards
What is genetic diversity?
Genetic diversity is the number of different alleles of genes in a species or population.
How can genetic diversity with in a population increase?
Different alleles can be introduced into a population by individuals from another population which migrate into them and reproduce. This is known as gene flow
What does genetic diversity allow for which is needed for evolution?
Natural selection
What is a genetic bottleneck?
A genetic bottleneck is an event that causes a big reduction in a population, e.g. when a large number of organisms wthin a population die before reproducing.
This reduces the number of different alleles in the gene pool and so reduces genetic diversity.
The survivors reproduce and a larger population is created from a few individuals.
Explain how a genetic bottle neck leads to decreased genetic variation.
The genetic bottleneck reduces the number of different alleles in the gene pool because certain types of alleles in the population of organisms will have a lower or higher chance of surviving the event that causes mass death to the population.
As a result of this, the organisms with the best alleles suited for survival are the most likely to survive the genetic bottleneck and be part of the very small population at the end of the event. And vice versa, the organisms with the worse alleles suited for survival are much more likely to die and so have a lower chance to pass the allele, even with the chance of extinction for that certain characteristic.
The organisms will then reproduce to bring numbers back up after the event, and because a majority will now have the favorable allele due to natural selection, allowing them to survive, a high majority of the population will have not much genetic diversity between them, with some alleles before the genetic bottleneck even becoming extinct.
Here’s a good image to help: https://d20khd7ddkh5ls.cloudfront.net/bottleneck_effect_3.jpg
Briefly describe natural selection.
Natural selection is a mechanism of evolution. Organisms that are more adapted to their environment are more likely to survive and pass on the genes that aided their success. This process causes species to change and diverge over time.
Explain the process of natural selection.
A gene mutation occurs within an organism in a species which positively benefits the organism.
Since there is competition for food and resources, individuals that have an allele that increases their chance of survival are more likely to survive, reproduce and pass on their genes (including the beneficial allele) than the organisms which do not have the allele.
This means that a greater proportion of the next generation inherits the beneficial allele.
They, in turn are the most likely to survive, reproduce and pass on their genes.
So the frequency of the beneficial allele increases from generation to generation.
Over generations, this leads to evolution as the advantageous alleles become more common in the population.
What is variation?
Variation is the differences between characteristics of the same species.
Tawny owls show variation in color. There are light grey and darker brown owls.
Before the 1970s, there were more grey owls than brown owls in Finland. Since then, climate change has been causing a decrease in the amount of snowfall in Finland. During this period, the darker brown owls have become more common.
Suggest why the brown owls are better adapted to being in an area with less snowfall than the grey owls.
Explain how the brown owls have become more common.
The reason why brown owls are adapted to being in an area with less snowfall than grey owls is because they benefit from camouflage - brown owls are able to better blend into the ground with less snowfall, making them much harder to detect and so become more stealthy, increasing their chances of survival.
Grey owls will suffer from less snowfall as they will have less time to camouflage and so they will be more open to attacks from predators as they are much easier to spot as they will not blend into the environment as often, making the chance of survival lower.
In a population, there are grey owls and brown owls. Initially, the rate of snowfall in Finland was high, but after the 1970s, the rate of snowfall in Finland decreased, causing an increase in brown owls.
This is because, as the rate of snowfall decreases, the brown owls will find it much easier to compete for food against it’s grey counterpart as the presence of snow, which once offered camouflage to the grey owls, has decreased, lowering their chances of survival. In contrast, the brown owls did not benefit from the presence of snowfall, and so the decrease in the rate of snowfall will allow them to have a higher chance of survival. This is because the camouflage for brown owls are increasing following the decrease in snowfall compared to the grey owls, which are decreasing.
The brown owls will find it increasingly easier to hunt for food as predators find it harder to spot them, and so will have a higher chance to survive, leading to offspring which will pass down the beneficial allele, which over generations will increase the presence of the allele in the population as it is advantageous, leading to a higher presence of brown owls.
Define directional selection.
Directional selection is a type of natural selection where the the individuals with a certain allele are more likely to reproduce than before, causing the allele frequency to shift in one direction, responding from something like an environmental change.
Define stabilizing selection.
Stabilizing selection is a type of natural selection where the individuals with a certain allele that has the best chance of survival in the environment end up taking up a very high percentage of the population as the environment is not changing, and so a very high amount of the population have the same combination of allelles for a certain characteristic.
Give an example of directional selection.
Antibiotic resistance
Describe how antibiotic resistance causes directional selection, starting from when the antibiotic is introduced into the population.
Firstly, the antibiotic will be introduced into the population of bacteria.
Mutations in the genes of bacteria will allow some bacteria to have immunity to that certain antibiotic. At this point, the antibiotic resistant bacteria will be a minority of the population.
The antibiotic will kill almost all the bacteria which do not have the mutation required to be resistant to the antibiotic.
The resistant bacteria will have almost no competition for food or resources after the antibiotics wipe out most of the population, allowing it to survive and reproduce with a much higher chance.
The resistant bacteria, since it is more likely to survive, has a much higher chance to reproduce and pass on offspring with the genes that have antibiotic resistance.
As a result of this, after multiple lifecycles of bacteria, the antibiotic resistant bacteria will be the majority in the population, compared to before the antibiotic was introduced to the population.
In some farms, animals are often given antibiotics in their food.
Scientists investigated whether those farm animals had antibiotic-resistant bacteria in their intestines. They tested the bacteria for resistance to two antibiotics, tetracycline and streptomycin.
29% of bacteria had resistance to Tetracycline.
13% of bacteria had resistance to streptomycin.
Suggest and explain a reason why there is a difference in results of antibiotic resistance.
Because Tetracycline might’ve been used more often than streptomycin, causing a higher rate of antibiotic resistance within the population.
or:
Because there might be a higher frequency for mutations which offer resistance to Tetracycline compared to Streptomycin, causing a higher rate of initial antibiotic resistance. This increases the rate of antibiotic resistance within the population further on.
Bacterial meningitis is a potentially fatal disease affecting the membranes around the brain. Neisseria meningitidis (Nm) is a leading cause of bacterial meningitis.
Penicillin has been the antibiotic of choice for the treatment of bacterial meningitidis. Since the year 2000, strains of Neisseria meningitidis that are resistant to penicillin and other antibiotics have been discovered in the UK.
Describe how a population of Neisseria meningitidis (Nm) can because resistant to these antibiotics.
A mutation within the population of Neisseria meningitidis might occur which offers bacterial resistance to an antibiotic, for example, Penicillin.
When the population of Neisseria Meningitidis becomes exposed to penicillin, the minority population with the antibiotic resistant gene will survive while most of the other bacteria will be wiped out.
Since the antibiotic resistant bacteria are one of the few surviving, there is much less competition between other bacteria for food and resources. Therefore, it is much easier to survive and reproduce.
Due to the increase in reproduction of this certain antibiotic resistant bacteria, this will cause an increase in the population of the bacteria which express the gene needed for antibiotic resistance.
As a result of multiple generations of bacteria being exposed to penicillin, the majority of Neisseria meningitidis in that population will have inherited the gene needed for antibiotic resistance as a result, becoming the majority of the population.
This process will repeat and apply for every single antibiotic in the list given until the population of bacteria will be resistant to all 3 antibiotics listed.
What is a gamete?
Gametes are an organism’s reproductive cells. For example, sperm and egg cells in humans.
They join together at fertilization to form a zygote, which develops into a new organism.
What is a diploid cell?
A diploid cell has 2n chromosomes.
This means that the cell contains two copies of each chromosome.
Are normal body cells diploid or haploid?
Diploid
The cells have two copies of each chromosome.
Are gametes haploid or diploid?
Haploid
What is a haploid cell?
A haploid cell has ‘n’ chromosomes.
This means the cell contains only one copy of each chromosome.
Label A,B and C as either haploid or diploid cells:
https://media.discordapp.net/attachments/352951793187029005/813121102581596170/unknown.png?width=608&height=562
A = Diploid
B = Diploid
C = Haploid
Describe what happens in fertilization between a sperm and egg cell.
A haploid sperm fuses with a haploid egg, making a cell with the normal diploid number of chromosomes, known as a zygote.
Half of these chromosomes are from the father, and half are from the mother.
Describe how fertilization increases genetic diversity.
During sexual reproduction, any sperm can fertilize any egg - fertilization is random.
Random fertilization produces zygotes with different combinations of chromosomes to both parents.
This mixing of genetic material in sexual reproduction increases genetic diversity within a species.
What is Meiosis?
Meiosis is a type of cell division that takes place in the reproductive organs, wherein the product are four genetically different daughter cells.
Two gametes fuse together to create a zygote.
Does the zygote become diploid or haploid? Describe how.
I would recommend trying to draw this out, showing the chromosome contents from both gametes into the zygote and what becomes of it.
A gamete from the father (sperm) and a gamete from the mother (egg) are both haploid, meaning that they only have one of each chromosome.
At fertilization, when the sperm fuses with the egg, a cell is made with the normal diploid number of chromosomes, having two of each chromosome, wherein half is from the father and the other half is from the mother.
Describe what happens to a reproductive cell right before meiosis happens.
The cell unravels its DNA, replicating it in the process, creating two copies of each chromosome (2 x 2n).
What does ‘n’ mean?
The cell contains only one copy of each chromosome.
Haploid
What does ‘2n’ mean?
The cell contains two copies of each chromosome.
Diploid
What does ‘2 x 2n’ mean?
The cell contains two copies of each chromosome, which are double armed chromosomes as they have two chromatids joined by a centromere.
Describe the process of meiosis.
Before meiosis, the cell replicates and unwinds it’s DNA, doubling the amount of chromosomes it contains.
The cell then condenses it’s DNA, forming double armed chromosomes, each made up of two sister chromatids joined up by a centromere and in homologous pairs.
The cell then goes through the first meiotic division, wherein the cell divides, separating the homologous pairs apart and halving the number of double armed chromosomes in each of the two cells, meaning there is now only one pair of each chromosome in each cell.
The cell then goes through the second meiotic division, wherein the two cells divides to create, in total, 4 new, genetically different daughter cells which are haploid, meaning that they have only one copy of each chromosome.
Describe the process of crossing over.
The process of crossing over occurs in the first round of meiotic division, wherein each homologous pair of chromosomes come together and pair up.
From there, the chromatids nearest to each chromosome in the pair twist around each other and bits of chromatids swap over, forming a bivalent.
The chromatids still contain the same genes, but can now have a different combination of alleles, increasing genetic variation.
Describe what independent segregation refers to, as well as how it increases genetic diversity.
Each homologous pair of chromosomes consist of one chromosome from the dad (paternal) and one chromosome from the (mum).
During the first round of meiotic division, the homologous pairs are separated, and independent segregation refers to the fact it’s completely random which chromosome from each pair comes into which daughter cell.
So the four daughter cells produced by meiosis have completely different combinations of those maternal and parental chromosomes.
This ‘shuffling’ of chromosomes leads to genetic variation in any potential offspring.
Describe how crossing over leads to increase genetic variation.
During crossing over, non-sister chromatids are exchanged with each other in a homologous pair.
Crossing over creates new combinations of genes in the gametes that are not found in either parent, contributing to genetic diversity.
As well as this, crossing over ensures that each gamete produced as a result of meiosis have different chromatids to each other, and therefore a different set of alleles, which increases genetic variation.
This diagram features the process of meiosis.
Fill in the graph:
https://media.discordapp.net/attachments/352951793187029005/814602641765302322/unknown.png?width=467&height=563
Only show 2 chromosomes, not all 23.
https://media.discordapp.net/attachments/352951793187029005/814603271405568050/unknown.png?width=485&height=563
Does crossing over occur in Meiotic division 1 or 2?
Meiotic division 1
Give two differences between Meiosis and Mitosis.
Differences:
Meiosis produces 4 daughter cells. Mitosis produces 2.
Meiosis produces genetically different daughter cells. Mitosis produces genetically identical daughter cells.
Meiosis produces cells with half the number of chromosomes than the parent cell.
Mitosis produces cells with the same number of chromosomes as the parent cell.
Meiosis has 2 nuclear divisions, Mitosis is 1.
The fertilization of a gamete that causes down syndrome must mean it has what features?
The gamete must have two of the same chromosome, wherein it must be chromosome 21.
This ensures the gamete, when fertilized with the sperm will achieve an extra chromosome 21, having three, than the usual two, causing down syndrome.
How is a chromosome mutation caused?
Errors during meiosis
What do chromosome mutations lead to, granted that the mutated gamete gets fertilized?
Chromosome mutations lead to inherited conditions because the errors are present in the gametes which will divide by mitosis holding the error for the rest of its life.
Give one type of chromosome mutation.
Non-disjunction
