6.3 Evolution. Flashcards
(21 cards)
What is evolution?
A change in allele frequency.
How does evolution occur?
Natural Selection
What are the steps of natural selection?
- Selection Pressure.
- Individuals with an advantageous allele survive.
- These survivors reproduce, and pass on advantageous allele.
- Over time frequency of this allele increases.
What is Stabilizing Selection?
When environment is stable, individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce.
What is Directional Selection?
When there is a change in the environment, individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce.
What is genetic drift, and how does it work?
Individuals in a population show variation in genotypes.
By chance the allele for 1 genotype is passed onto the offspring more often than others.
Number on individuals with the allele increase.
If by chance the same allele is passed on more often again and again, it can lead to evolution.
Does genetic drift have a greater effect on larger or smaller populations?
Smaller populations.
It has a greater influence
In larger populations any chance variations in allele frequency tend to even out across the whole population.
What is a genetic bottleneck?
An event that causes a big reduction in a populations size, leading to a reduction in gene pool.
(A natural disaster)
What’s the founder effect?
Describes what happens when just a few organisms from a population start a new population. There are only a small number of different alleles in the initial gene pool.
What is the Hardy - Weinberg Principle?
It predicts that the frequencies of alleles in a population won’t change from 1 generation to the next.
What conditions are required for Hardy - Weinberg principle to be true?
Large population
No immigration or emigration
No mutations
No natural selection
Random mating.
What is the Hardy - Weinberg Equation to predict Allele Frequency?
p + q = 1
p: Frequency of dominant allele
q : Frequency of recessive allele
What is the Hardy Weinberg equation to predict Genotype frequency.
p^2 +2pq + q^2 = 1
p^2: frequency of homozygous dominant genotype
2pq: Frequency of heterozygous genotype
q^2: Frequency of homozygous recessive genotype.
What is Artificial Selection?
Breeding individuals with desirable traits.
What are the benefits of artificial selection?
Offspring produced which have desirable traits.
Negatives of Artificial selection?
Reduces gene pool:
As a result lower chance Alleles could be resistant to a disease.
Potentially useful alleles are accidentally lost.
What is Speciation?
The development of a New Species.
How does allopatric speciation occur?
- A physical barrier separates a population, and stops interbreeding between populations.
- Populations adapt to new environments (Natural selection)
- Allele and phenotype frequency change leading to the development of new species.
How can reproductive isolation occur?
Seasonal changes - Develop different mating seasons.
Mechanical Changes - Changes in genitalia prevent successful mating.
Behavioral Changes - Group of individuals develop courtship rituals that aren’t attractive to the main population.
What is allopatric speciation.
Speciation caused by a physical barrier.
What is sympatric speciation.
Speciation which occurs without a physical barrier.
Much less common than allopatric speciation.
