4.2.2 Natural selection and microevolution Flashcards
What is the founder effect
A small group of indiviuals are separated by a population and colonise a new environment. This reduces the gene pool
Explain what disruptive selection does
Its when both extreme phenotypes are more fit than those in the middle. Over time can lead to two distinct species
*Makes bimodal spread with an increased genetic variation
Explain what directional selection does
Its when one extreme phenotype is more fit than all the other phenotypes
*Shifts the curve to the favourable phenotype and the future generations have a more homologous population
*ADVANCED QUESTION*
Predict the next generation of 20 bunnies if 5/10 white bunnies died off
Explain the process of natural selection
As there is genetic variation in a population this means that there are individuals with an advantage in certain environments. These individuals are more likely to survive (AKA their viability), hence these individuals can reproduce (AKA their fecundity).
*if they were phenotypically and genetically identical, natural selection wouldn’t occur as no individual has an advantage over another
How does mutations play a role in natural selection
Mutations create genetic variation hence they enable natural selection to occur. Mutations will ONLY effect evolution if they are expressed in phenotypes
What does positive selection mean
selection that favours a heritable trait, resulting in that allele frequency in a population is likely to increase
Explain Gene flow
It occurs where alleles are added or removed from a gene pool (through migration), this process increases genetic variance
Harmful alleles and favourable alleles can be introduced, slowing down evolution (harmful) or speeding it up (beneficial as there is speciation)
Explain the process of genetic drift
It occurs by chance or random events cause unpredictable changes in allele frequencies from one generation to the next
*Differenct from natural selection as genetic drift does not necessarily favour individuals with an advantage, meaning an allele could be eliminated from a population even if it is a beneficial allele
Two driving processes: the bottleneck effect and the founder effect
What does negative selection mean
disfavours a heritable trait resulting in that allele being less frequent
Identify disadvantages of natural selection
If natural selection occurs, there is a loss of genetic variation which could be useful in the future should the environment change again
What are the three main types of phenotypic natural selection
- Stabilising selection
- Directional selection
- Disruptive selection
Explain what stabilising selection does
its when intermediate phenotypes are more fit than extreme ones
average species are more likely to survive over extremley positive + negative phenotypes
*they narrow the bell curve and hence the future generations result to have a larger portion of them being homologous for that phenotype
Explain the bottleneck effect
Results from climate change, natural disaster or human impacts. A drastic decline in population resulting in the population risking extiction and reduced genetic variation
How can mutations have a positive or negative effect on a population
The mutations can be beneficial (as they provide an advantage in an environment)
or they can be harmful (being a disadvantage in the environment)
