Week 12 Flashcards
What is microevolution?
How do populations evolve?
Change in the genetic characteristics of a population over time and a change in allele frequency in a population over time.
They evolve by mutations and from different alleles (mom and dad).
What is a gene pool?
What is an allele?
A gene pool is all the variants of allele in a population. It is the total genetic (think about alleles) diversity found within a population.
Alleles are the different variants or forms for that trait (traits are variations of those characteristics). Alleles are genes variation that arise by mutation and exist at the same relative locations on homologous chromosomes . This then determines the traits. They are a copy of a gene.
What causes new alleles to arise in a population?
What mechanism cause a change in allele frequency (change in gene pool)?
Mutations
Natural selection (the environment, pray, etc), genetic drift, genetic flow.
What are the mechanisms of microevolution?
- Natural Selection
- Mutation
- Sexual Selection
- Genetic Drift
- Gene flow
Describe Mutations
They are random, they may occur anywhere in genome (coding or non-coding DNA, regulatory sequences…)
They are the source of all new genetic variation which gives us new alleles.
New alleles may be kept in it disappear from population.
There are also chromosomal mutations that may occur: e.g. duplication, inversion, deletion, etc
What may cause a new allele to increase (or decrease) in frequency?
The environment. It can be beneficial or detrimental. The only way to know that it is if we survive or not.
Describe Natural Selection
Certain phenotypes that increase reproductive success are “selected” by the environment.
Alleles responsible for those phenotypes increase in frequency in population.
⭐️ Result in adaptation: Increased fitness (“fit” between population and its environment) (they fit better so they will survive better)
Adaptive evolution is always ongoing, as environment changes continuously.
Selection can only occur if there exists variation in heritable traits, ultimately caused by mutations!
Example: The white rabbit who lives in a place with a lot of snow will survive and the other ones no, because they can’t blend in their environment.
What modes of natural selection
A) Stabilizing selection: the most common/average phenotype in the population is selected for and continues to dominate in future generations (reduces both extremes and go up)
B) Directional selection: individuals with traits on one side of the mean in their population survive better or reproduce more than those on the other
C) Disruptive selection: It favors both extreme genotypes. Over time it could lead to speciation (macroevolution)
Describe Artificial Selection
- It is a special case of natural selection
- Humans play role of environment and select individuals with desired phenotypes (Humans are the ones who selected, for exemple, berries, birds, animals, etc)
Describe Sexual Selection
- Phenotypes that enhance ability to obtain mates and increase reproductive success are selected (it makes them have more chance of mating since they could be for example more pretty)
- Alleles responsible for those phenotypes increase in frequency in population
- Results in sexual dimorphism (difference in size or appearance between the sexes of an animal in addition to difference between the sexual organs themselves)
- May result a costly trade-offs (it can create two extremes of males and females)
Describe genetic drift and what it includes
- It is a random sampling (it is chosen randomly)
- It make changes in allele frequencies in small populations
- It decreases genetic diversity (because there will be almost only one species left)
- It is non-adaptive (failing at contributing to the fitness)
Includes:
A)Chance events in small populations
B)Genetic bottleneck (Large population that has a sudden reduction in size due to natural disasters, food source reduction,…, which creates a change in the allele frequency and so the genetic diversity is decreased)
C)Founder effect (it is the reduction of genetic variation, by the change of allele frequency, that results when there is immigration of a few individuals from an original population to a new area)
Describe gene flow
- It makes alleles frequencies change due to migration of individuals between populations (there is a lot of migration)
- May increase, decrease or have no effect in fitness
What is Allele frequency
It refers to how common an allele is in a population.
It is determined by counting how many times that allele appears in the population then dividing by the total number of copies of the gene.
If evolutionary mechanisms lead to LOSS in genetic (allele) diversity, then what does INCREASE diversity?
Mutations
Explain the Hardy-Weinberg equilibrium principle and requirements
It states that allele frequencies in population remain constant generation after generation ONLY IF THESE CONDITIONS ARE MET:
- Very large population=No genetic drift
- No gene flow=No migration
- No mutations=No new alleles added to gene pool
- No sexual selection=Mating is random
- No natural selection=All traits aid equally in survival
