How species evolve 11 Flashcards
Point mutation
- a mutation that alters one nucleotide
- example: silent, missense, and nonsense mutation. ( addition or deletion; frameshift)
- ( singular nucleotide frameshift muatation can be considered as point mutation but not double nucleotide)
Nonsense mutation
- a mutation in when a nucleotide is substituted
for another, changing the codon to
a stop codon, ceasing transcription
on the gene. - Thus, gene will not be completely transcribed, resulting in a polypeptide that is too short to function
- most dangerous sub mutation as it permantly ends transcription genes
Silent mutation
- a mutation when a nucleotide is substituted for another, changing the codon, while coding for the same amino
acid. - Thus, there is no effect on protein structure, because redundancy
Missense mutation
- a mutation in when a nucleotide is substituted
for another, changing the codon that codes for a differnt amino acid. - thus, this alters the primary structure of the polypeptide –> affects function of protein
Frameshift mutation
- a mutation that involves the insertion or
deletion of one or two nucleotides, - affecting every codon from thatpoint forward as the reading frame is altered( as it is shifted )
- Thus, major disruptions to structure and function
- e.g. can be base insertion/ deletion mutation
Reading Frame
the order in which nucleotide triplets or codons are
read to match complementary base
base insertion mutation FS
a nucleotide is added to a gene,
affecting every codon from that
point forward
base deletion mutation
a nucleotide is removed from a gene,
affecting every codon from that
point forward
Block mutations
-affects a large chunk of DNA, or an entire geneby altering the structure of a chromosome by deletion, duplication, inversion, and translocation of clusters of nucleotides
Block mutation: deletion mutation
- a section of DNA is removed from a chromosome, shortening the DNA.
Block mutation: duplication mutation
- a section of DNA is replicated, lengthening the DNA
Block mutation: inversion mutation
- a section of DNA has its sequence reversed.
Block mutation: translocation mutation
-when two sections of DNA on different chromosomes
switch places.
aneuploidy
- when a cell or organism varies in the usual number of chromosomes in its genome by the addition or loss of
a chromosome - seen in individual’s karyotype and during stem from issues during meiosis
Polyploidy
- when an organism contains additional sets of each
chromosome in its genome. - addition set of chromosome in embryos are fatal and thus, invidials can’t survive as halpoid ( N).
- common in other organisms such as plants as an advantage is it increases size and hardness in fruit but they are unale to reproduce sexually
What do mutation do to genetic diversity?
- mutation introduces new alleles into a population and this increases genetic diversity
- mutation can be beneifical, neutral or delterious
Mutagen
agents that can cause
mutations in DNA
- e.g. UVradiation–> skin cancer
Deleterious
alleles that have an
overall negative effect on individual
fitness when expressed
Alleles
variants of a gene
Allele frequency
the proportion of
certain alleles in a gene pool
gene pool
all the genes in
a population
Germline cell
cells involved in the
generation of gametes
in eukaryotes( reproductive system)
phenotype
the physical or biochemical characteristics of an organism, resulting from expression of a gene (or set of genes) and interaction with the environment
somatic cell
any cell in an
organism that is not a germline cell, body cells and when mutations occur it cannot be inherited
List examples of aneuploidy conditions
- Down syndrome
- Edwards syndrome
- Klinefelter syndrome
- Turner syndrome
Mutation and common symptoms of Down syndrome
- Trisomy 21
-Decreased muscle tone, short neck, flattened
facial profile and upward slanting eyes
Mutation and common symptoms of Edwards syndrome
- Trisomy 18
-Very small weight, small head, long and
underdeveloped fingers
Mutation and common symptoms of Klinefelter syndrome
- XXY
- Typically tall, infertile, enlarged breast tissue. Only
affects phenotypic males
Mutation and common symptoms of Turner syndrome
- X0
- Typically infertile, short height and fused neck and
head. Only affects phenotypic females
Steps of Natural selection
- Many physical, biochemical or behavioral variation in phenotypes between individuals in a population
- variation is heritable
- Specific selection pressure causes a struggle for survival.
- individuals with advantageous phenotype survive and reproduce
- Pass their alleles onto the next generation.
- This changes the allele frequencies in the population as the trait becomes more common
Steps of Natural selection: 1. Variation
- Individuals in a population vary genetically. This leads to phenotypic differences.
e. g.
- One species of moth has two genetic
variants: black and white.
Steps of Natural selection: 2. Heritability
- These traits - whether advantageous
or disadvantageous for survival and reproduction - alleles can be passed on from parents to offspring
e.g.
- Body colour is heritable - parents with white body colour are likely to have whit body offspring , while parents with black
body colour are likely to have black body offspring.
Steps of Natural selection: 3. Selection pressure and struggle
- The struggle is caused by a selection pressure. This is the factor that impacts an organism’s ability to reproduce and survive.
-Like environmental (e.g. predation, temperature increase, limited resources) or population factors (e.g.
excess offspring and high competition)
e.g.
- The industrial revolution occurs, and there is
an increase of soot in the air. This makes trees black.
-White moths thus, become very visible, so birds prey heavily on white moths.
- The birds determine who lives and who dies, so the birds are the selection pressure.
Steps of Natural selection: 4. Fitness
-Individuals with phenotypes that make them fitter under the local selection pressures reproduce more successfully and pass on the genes for the advantageous traits to their offspring.
e.g.
- Frequency of the allele for the black phenotype increases in the population,
as they are camouflaged from predators.
- The frequency of the allele for the white phenotype decreases
Students can struggle to answer short answer questions on natural selection the trick?
The trick is that most
questions are just asking you to explain the process of natural selection in the given scenario. Start
by saying which trait is
1) variable, stating that this trait is
2) heritable, identifying the
3) selection pressure and explaining how this affects
4) fitness and phenotype of individuals over generations.
Case study: Charles Darwin 1835 Galapagos islands ( read)
- Charles Darwin was one of the key scientist behind the theory of evolution by natural selection.
- He observed ground finches comprised of unique beak shape
- Variation: variation in beak shape among the ancestral population of mainland finches
- Heritability: this variation was heritable
- struggle: upon migration to Galapagos island, food available was different compared to the mainland.
- Some finches with specific beak shapes were better at finding and consuming Galapagos island food. - Fitness: the finches that had beak shapes that effectively consume available food survived and reproduces more successfully.
- Their offsprings inherited the parents’ beak shape and over generations separate species with beak shapes specialised to the food type on their island
Case study: Crane toads ( read)
- Variation: : there is variation in red-bellied black snake length and behavioral response to cane toads and in their susceptibility to toad poison.
- Heritability: variation inheritable
- Struggle: the cane toads provide the selection pressure that causes a struggle for survival among red-bellied black snakes.
- Fittness: snakes that avoid eating the toads, or are less affected by their poison, survive and produce more offspring. These advantageous traits are passed onto the next generation.
The effect of natural selection on allele frequencies
- selection pressure determines fitter phenotypes–> traits will be better represented in the next generation
- advantageous traits–> common (evolution)
- Species with large amounts of genetic variation are less likely to go extinct.
–> BC a higher chance of possessing a favorable genetic trait help it survive if a new selection
pressure arises.
– e.g. disease resistance. Populations with more diverse gene pools have greater diversity in their immune systems. This generally makes them more tolerant of individual disease outbreaks.
– Low genetic variation can also cause problems for species, as inbreeding is more likely to occur. Inbreeding can lead to a high prevalence of disadvantageous alleles.
– Small populations are more likely to have low genetic variation than large
Natural selection
Selection pressure is naturally occuring
Selection pressure
- a factor in the environment (e.g. limited resources, deforestation, changing
temperature, predation) - that impacts an individual’s ability to survive and reproduce.
- It causes a struggle for survival
evolution
the change in the genetic makeup of a population over successive generation
genetic variation
Differences in DNA sequences between individuals
Gene Flow
Introduction or removal of alleles from population due to migration
Gene flow – Migration: immigration
movement into a population
Gene flow – Migration: emigration
movement out of a population
How can migration occur
- bc populations are physically close together
- due to external forces ( e.g. natural disasters, clearing of geological barriers between population)
The effect of gene flow on allele frequencies - What does immigration and emigration effect?
affect allele frequencies: the proportion of certain alleles in gene pool
Genetic drift
The dramatic change in allele frequencies due to chance event / random occurrence
( either bottleneck effect or founder effect )
Genetic drift: Bottleneck effect
- when a large proportion of a population is removed/ wiped out due to a chance event ( Natural diaster/ overhunting/ oil spills)
Genetic drift: Founder effect
- The reduction in genetic diversity that occurs
- when a small group of individuals colonise a new population.
- result: small gene pool and genetic diversity
e.g. 10 green beetles left multi-coloured original population to form new population–> genetic diversity is lowered than the original. But if the original beetles were all green and the new gene pool resemble the initial this is not an example of the founder effect.
What do both founder and bottleneck effects both decrease?
- Founder and bottleneck effects both decrease genetic diversity in a population,
The effect of genetic drift on alleles: risk of reducing genetic variation
- Inbreeding–> keeps harmful alleles in the gene pool
- Low genetic diversity -> vulnerable to new selection pressures.
Since genetic drift are more apparent in a small population, what can lessen its impact
- Random events of the genetic drift ( founder and bottleneck effect) can be lessened on a larger population
e. g
- Bc 10 beetle, 1 die = losing 10% of gene pool
- 100 beetle, 1 die= losing 1% of gene pool
inbreeding
sexual reproduction between two related individual
What is speciation
- populations genetically diverge until they become different species
- diverge through evolutionary processes such as mutations, natural selection, genetic drift and gene flow
- Speciation can be categorized as allopatric speciation or sympatric speciation
Species
a group of individuals able to breed with each other and produce viable and fertile
offspring
viable
able to survive
Fertile
having the ability to
produce offspring
Allopatric speciation
Process by which population genetically diverge until they become different species due to a geographical barrier
sympatric speciation
the divergence of a species from
an original species without the
presence of a geographical barrier
geographical barriers
a physical factor that prevents gene flow, and thereby stops two populations
from breeding together
The process of allopatric speciation
- A geographical barrier separates a population of same species and no gene flow can occur.
- : Different selection pressures act upon
each population, - Eventually, so much genetic variation
has accumulated that the two populations can no longer interbreed
even if the geographic barrier is removed and have become new species
How to distinguish different species
- cannot breed to produce viable and fertile offspring.
- comparing amino acid sequences, DNA sequences, or structural features
An example of allopatric speciation: snapping shimp population
- The population was separated by the Isthmus of Panama, a stretch of land in Central America that formed around 3 million years ago.
- Populations on either side of the landmass were subject to different selection pressures.
- Over time, differences accumulated and new species formed
Example of selection pressure
Resource availability – Presence of sufficient food, habitat (shelter / territory) and mates.
Environmental conditions – Temperature, weather conditions or geographical access.
Biological factors – Predators and pathogens (diseases)
What population has a greater chance of undergoing/ surviving allopatric speciation
if there is already a large amount of genetic variation prior to geographic barrier
- This provides species with a greater ability to survive the differing selection pressure created by new environment
Identify whether the amount of gene flow increases or decreases as the distance between two populations increases. Justify your answer.
SOLUTION
As the distance between two populations increases, gene flow decreases as individuals are less likely to travel a further distance to migrate to another population.
Explain how the genetic diversity of a population is affected by a natural event such as gene flow.
SOLUTION
- Gene flow can increase the genetic diversity of a population through immigration introducing new alleles into a population.
- However, through emigration, genetic diversity can decrease as alleles are leaving a population.
With reference to selection pressures, explain the importance of genetic diversity in a population.
- Low genetic diversity =>population susceptible to new selection pressures
- bc there is less chances of organism having the advantageous allele to selection pressure.
Therefore, a greater variation enables a species to thrive under many different selection pressures.
When will gene flow unlikely to occur
When the two population are separated by a significant distance.
Four healthy individuals from the dolphin population (two male, two female) were taken into captivity and bred intensively over several generations in order to dramatically increase the population size of dolphins.
Outline an issue with such a breeding program, referring to the genetic diversity and fitness of the future population.
- The sample used in the breeding program (four dolphins) is small and would cause the founder effect.
- The genetic diversity of the resulting offspring from this breeding program would be as low as the limited diversity in the initial four dolphins.
- Low genetic diversity is dangerous for a population since there will be a lower chance of advantageous alleles existing in the gene pool which are important for safeguarding against future selection pressures that may threaten the species’ survival.
- Furthermore, inbreeding between closely related founder dolphins would increase detrimental alleles in the population.
- Detrimental alleles reduce the fitness of individuals and cause further reduction in the population size until the species become extinct
- Name a feature that scientists would look for in the forest environment to support the occurrence of allopatric speciation.
- xplain how geographical barries could contribute to allopatric speciation.
- Geographical barrier
- The geographic barrier prevents two populations from breeding together by preventing gene flow.
- Therefore different selective pressures may act on population resulting in speciation.
if the different cockroach species could interbreed and produce viable and fertile offspring, would this disprove that they evolved through allopatric speciation? Justify your response.
Yes, this would disapprove the hypothesis. As two individuals who breed and produce viable and fertile offspring must belong to the same species.
Explain how scientists could conclude that the populations were different species.
- The scientists could breed an individual from each population with one another.
- If they cannot produce viable or fertile then they are considered separate species.
Identify two natural methods that cause variation in a population.
Mutations and sexual reproduction
Suggest one reason why allopatric speciation may not have affected these populations
The two populations were not exposed to different selection pressures despite their distance
Isolation of these two populations may have occurred more recently meaning that not enough time has passed for them to diverge into separate species.
The cattle tick may have been introduced from one of these countries to the other via migration or artificial means.
What is the major difference between artificial and natural selection?
- natural selection: the selection pressure is determined by the natural environment
- artificial selection: selection pressure is deliberately human-imposed, as Humans select for the desired trait, or remove traits
Explain two potential unintended consequences of artificial selection.
In artificial selection, only a part of a population is selected for breeding.
- this reduces genetic variation in the population and an increased risk of inbreeding
The consequences of this are
- a lowered adaptive potential to changing environments
- increased expression of deleterious recessive alleles due to inbreeding
founder effect( answer style)
The founder effect occurs when a small number of individuals in a population colonise a new region of land.This new population is unrepresentative of the original and has a lower genetic diversity
Steps for artificial selection
- Variation: the population has a phenotypic difference
- Heritability: traits can be passed on from parent to offspring
- Intervention: Selection altered by human
- Breeding: breeding population reproduces continues over generations.
