3.4.4 Genetic Diversity Flashcards
What is there a variety of if there’s a high genetic diversity
Lots of different alleles
What are alleles
Different versions of a single gene
Define genetic diversity
The number of different alleles in a species/population
2 things that increase genetic diversity in a population
Mutations
Different alleles being introduced
What do mutations in dna form
New alleles
What’s gene flow
Different alleles being introduced into a population, when individuals from another population migrate into them + reproduce
What does genetic diversity allow to occur
Natural selection
What reduces genetic diversity
Genetic bottlenecks
Define genetic bottleneck
An event that causes a big reduction in a population (die before reproducing )
How does a genetic bottleneck cause a decrease in diversity
It reduces number of different alleles in the gene pool
What’s a gene pool
Complete range of alleles in a population
After a genetic bottleneck, who create a larger population
Survivors reproduce + a few individuals create a larger population
What effect is a type of bottleneck
The founder effect
What’s the founder effect
What happens when just a few organisms from a population start a new colony with only s small number of different alleles in the initial gene pool
What can the founder effect occur due to
Migration -> geographical separation
What does natural selection increase
Advantageous alleles
What’s natural selection
When some mutations can produce beneficial alleles, helping the organisms survive -> the frequency of this allele will increase
2 key factors in evolution
Adaption
Selection
What has evolution led to
A huge diversity of species living
3 adaptations that help organisms survive
Behavioural adaptations
Physiological adaptations
Anatomical adaptations
Example of a behavioural adaptation
‘Play dead’ to escape attack
Example of a physiological adaptation
Brown bears hibernate in winter + lower their metabolism, conserving energy
Example of an anatomical adaptation
Whales have thick blubber to keep warm
2 types of selection that affect allele frequency
Stabilising selection
Directional selection
Example of something that shows directional selection
Antibiotic resistance
Describe what happens in antibiotic resistance (directional selection)
- some individuals have allele giving them resistance to an antibiotic
- population is exposed to antibiotic, killing any bacteria without the resistant allele
- resistant bacteria survive + reproduce, passing on the allele giving the antibiotic resistance to their offspring
- after some time, most organisms will carry the antibiotic resistance allele
How is the mean in the offspring different to the mean in the parent (antibiotic resistance - directional selection)
Mean shifts right in offspring (higher antibiotic resistance)
Example of stabilising selection
Human birth weights
What’s directional selection
Where individuals for alleles for an extreme type of characteristics are more likely to survive and reproduce. Could be in response to an environmental change
What’s stabilising selection
Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce
It occurs when the environment isn’t changing and it reduces range of possible characteristics
Describe human birth weight being an example of stabilising selection
- humans have a range of birth weights
- very small babies are less likely to survive
- giving birth to large babies can be difficult
- conditions are most favourable for middle-sized babies - so wight kg human babies tends to shift towards middle of the range
Why are very small babies less likely to survive
They find it hard to maintain their body temperature
