Genetic Diversity and Natural Selection Flashcards
What are alleles?
Different versions/forms of the single gene
What is genetic diversity?
Number of different alleles of genes in a species or population
What factors increase genetic diversity within a population?
- Mutations in the DNA- forming new alleles
- Different alleles being introduced into the population when individuals from another population migrate into them and reproduce - gene flow
What is gene flow?
Different alleles being introduced into the population when individuals from another population migrate into them and reproduce
What is a population?
A group of organisms of one species living in a particular habitat
What is a gene bottle neck?
An event that causes a big reduction in a population e,g when large number of organisms within a population die before reproducing
What is the effect of genetic bottleneck?
- Reduces the number of different alleles in the gene pool - reduces genetic diversity
How is a larger population produced from genetic bottle neck?
Survivors reproduce to create a larger population is created from few invidiuals
What is an example of a genetic bottleneck event?
Northern Elephant Seals
- These seals were hunted by humans in the late 1800s
- Their original population reduced to 50 seals since the produced population of 170 000
- Population has little genetic diversity compared to southern elephant seals who never suffered a reduction in their numbers
What does the founder affect describe?
What happens when a few organisms from population start a new colony and there is a small number of different alleles in the inital gene pool
What happens to the frequency in the founder effect?
- Frequency of each allele in new colony different to frequency in original population e.g allele rare in original population is more common in new colony - higher incidence of genetic disease
What else can the founder effect explain?
- Occur as a result of migration leading to geographical separation
- or
- new colony is separated from original population for another reason , such as religion
An example of the founder effect
Amish People
- Amish population of North America were descended from a small number of Swiss who migrated there
- Showed little genetic diversity
- Remained isolated from the surrounding population due to religious beliefs
- New alleles introduced - high incidence of genetic disorders
What do randomly-occurring mutations sometimes result in?
New allele being formed
Why new allele being formed is harmful?
Mutated allele quickly dies out
How are mutations useful? -NATURAL SELECTION
Can produce allele that is beneficial to the organism (an e.g protein produced works better than original) helping the organisms to survive in certain environments
When allele codes for characteristics, increase the chance of organisms surviving its frequency within the population increase
Process of natural selection:
- Indiviviudals have an allele that increase their chance of survival and reproduce to pass on their genes (including the beneficial allele) than invidiual with different alleles
- A greater proportion of the next generation to inherit this beneficial allele
- More likely to survive, reproduce and pass on genes
- Frequency of beneficial allele increases from generation to generation
- Over generations, this lead to evolution as the advantageous allele becomes more common in the population
Whats differential reproductive success?
Not all individuals are more likely to reproduce
Individuals that have an allele that increase their chances of survival and more likely to survive to reproduce and pass on their genes (including beneficial allele) than individual with different alleles
What are the both two key factors in evolution?
- Adaptation
- Selection
- (a gradual chance in species over time) (evolution led to huge diversity of living organisms in Earth)
Why are adaptations useful?
Help the organisms to survive in their environment
What are the different types of adaptations?
- Behavioural adaptation
- Physical adaptations
- Anatomical adaptations
What is a behavioural adaptation ?
Ways an organism acts increase its chance of survival and reproduction
e.g possums sometimes ‘play dead’ if they are being threatened by a predator to escape an attack
What is physiological adapatation?
Processes inside an organism’s body that increase its chance of survival
For example brown bears hibernate over winter. They lower teir rate of metabolism (all chemical reaction take place in body)
This helps to conserve energy so they don’t need to look for food in months when its scarce.
What are anatomical adaptations?
- Structural features of an organism’s body that increase its chance of survival
e. g whales have a thick layer of blubber (fat) which helps them to keep warm in the cold sea
Tawny owls show variation in colour. They are light grey owls and darker brown owls. Before the 1970s there are 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
a) Suggest why the brown owls are better adapted to living in an area with less snowfall than grey owls
e.g brown owls might be camouflaged better/blend in with landscape than grey pw;s
as there is no snow cover
this makes them less likely to be eaten by predator
Tawny owls show variation in colour. They are light grey owls and darker brown owls. Before the 1970s there are 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
b) Explain how brown owls have become more common
Brown owls are more likely to survive and reproduce when these is less snow cover
pass on their allele for darker/brown colouring to their offspring
Over time, the allele for brown colouring will become more common in the population
There are many different species of rat snake, all found in different habitats and with slightly different colorings. The black rat snake lives in wooded habitats and has a dark, brown-black coloring
Describe how natural selection could explain the evolution of a rat snake with black-coloring in a wooded habitat
As a result of a mutation, some individuals in the population have a darker coloring that helps to blend into the environment
This is beneficial as it helps to avoid predators and sneak up on prey-
More likely to survive and reproduce to pass on allele for darker coloring
Frequency of allele for darker coloring will increase
many more generations, most of the organisms in population will carry the allele for darker coloring
DDT is a chemical insecticide that was first used to kill malaria-carrying mosquitos around the time of WWII
In 1950s, DDT-resistance mosquitos began to appear in areas of widespread DDT use
Describe how DDT-resistance became widespread in some mosquito population
Some individuals in the population have a mutated allele that gives resistance to DDT
The population is exposed to DDT, killing the mosquitoes without the resistance allele
Individuals with resistance allele survive, reproduce and pass allele
Frequency of the resistance allele increase in population
many generations, most organisms in the population carry DDT-resistance allele
What is a gene pool?
Containing a wide variety of alleles
Explain how a difference in its DNA might lead to an organism having different appearances and hence the species showing greater genetic diversity
Different DNA
Different codes for amino acids - different protein shape - different protein function (e.g non-functional enzyme)
chance in feature determined by protein - altered appearence
greater genetic diversity
What is the difference between genetic diversity within a species and genetic diversity between species?
Within a species – there is diversity between the alleles
Between species – there is diversity between genes
Explain genetic diversity in the context of blood type in humans.
– all humans have the gene for blood type
-Different alleles determine the blood type
Identify two mechanisms that increase genetic diversity
– mutations
- alleles introduced by new individuals to the population (immigration)
Explain how a mutation can be positive?
– change in the base sequence
- codes for a different order of amino acids.
- this new protein has advantageous properties in survival and/or reproduction
Give one example of a natural event that reduces genetic diversity and one event linked to human interaction.
Natural: volcano, earthquake, flood, fire, meteorite, extreme weather etc.
Human interaction: deforestation, construction, global warming etc.
How do genetic bottlenecks occur and reduce genetic diversity?
– an event causes of large reduction in the size of a population
-there are fewer alleles so less diversity -the new population is created from fewer alleles
How does the founder effect differ from a simple genetic bottleneck?
– a few organisms from a population leave and form a new population
Why is a reduction in population size genetically disadvantageous?
– fewer alleles in the population
- more chance of inbreeding/one disease could destroy the whole population
What is meant by the term ‘survival of the fittest’?
Organisms that are better adapted have a higher chance of survival Therefore have more chance of reproducing and passing on their genes
What is the definition of a behavioural adaptation?
– the way in which an organism acts in order to increase its chances of finding food to survive and ultimately reproduce.
) What is the difference between anatomical and physiological adaptations?
- Anatomical is adaptations in the structure of the body
- Physiological are adapted processes within the body
What is evolution?
Change in allele frequency over time
