WEEK 2 Flashcards
Populations contain ample genetic variation
3 points to consider:
[] Evolve
[] useful tools
[] DNA testing shows
- For a population to evolve, it must contain genetic variation
- One of the most useful tools for both genetic mapping and analysis of population level variation is:
Single Nucleotide polymorphisms (SNP’s) - DNA testing shows the natural phenomenon generally have substantial variation
Many proposed that evolution of species occur by the process of natural selection;
What did Darwin propose?
He proposed that the evolution of species occurs by the process of “Natural Selection”
- Changes in Allele Frequency -
In the Hardy - Weinberg allows predictions of genotype Frequencies meaning that: “Proportions of Genotypes do change the population IF:
List the 5
- No mutation takes place
- No genes are transformed
- Random mating
- Population is very large
- No Selection occurs
What are the FIVE agents of Evolutionary change?
- Mutation Changes Allele
- Gene Flow
- Non random mating
- Genetic Drift
- Selections favors some genotype over others
What is “Mutation Changes Allele”?
- Mutation is the ultimate source of genetic variation because mutation rates are low which is not responsible for the deviations of the Hardy-Weinberg Equilibrium.
What is “Gene Flow”?
- Gene flow is the migration of new alleles into a population
- It can also introduce genetic variation and homogenize allele frequencies between populations
In regards to “Non-random mating”, What are the two types of mating? then explain both briefly.
Assortive Mating [Phenotypically Similar]
- Similar individuals tend to mate, which increases homogyzosity
Disassortive Mating [Phenotypically Different]
- Different individuals tend to mate, which produces excess heterozygotes
What does “Genetic Drift” refer to?
- It refers to random shifts in Allele frequency which it’s effects may be severe in small populations
What is the difference between
- Founder Effect
- Bottleneck Effect
?
- Selection favors some genotype over others -
List the 3 conditions when evolution by natural selection occurs when?
- Phenotype Variation must exist among individuals in a population
- Variation among individuals must result in a number of differences of the offspring surviving in the next generation
- Phenotype Variation must have a generic basis
List the other THREE factors that may also contribute to Selection
- Avoiding Predators
- Match Climate Conditions
- Pesticide and Microbial Resistance
- Quantifying Natural Selection -
Define “Fitness” and “Relative Fitness” in regards to phenotypes
- Fitness is defines as the “reproductive” success of an individual
- Relative Fitness refers to the success of one genotype relative to others in a population
Fitness may consists of many components, meaning that reproductive success is determines by: [3] points to consider
- How long an individual survives
- How often it mates
- How many offspring it has per reproductive event
Give an example of a fitness insect and fully describe the concept in regards to this
Water Striders
- Most fit genotype = Most number of offspring
- Large female = lay more eggs, but survive shorter
- Natural Selections Role in Maintaining Variation -
What are the 3 Roles?
- Frequency Dependent Selection
- Oscillating Selection
- Heterozygotes may exhibit greater fitness than homozygotes
What are the two roles that consist in the “Frequency Dependent Selection” ? and then explain both briefly.
Negative Frequency Dependent Selection
- Favors RARE phenotypes and maintains variation within a population
- Another cause is dependence of resource competition
Positive Frequency Dependent Selection
- Favors COMMON phenotypes and leads to decreased variation
- the rarer the genotype becomes, the greater chance it will be against it
List 2 key points about Oscillating Selection
- Favors ONE phenotype at one time and another phenotype
- IF environmental change is cynical, selection would favor the 1st Phenotype then another, maintaining variation
What is the 3rd Role? + explain it briefly
- In some cases, heterozygotes may exhibit greater fitness than homozygotes
- It advantages favors individuals with BOTH alleles
[20.6] Selection Acting on Traits Affected by Multiples Genes
What are the THREE types of Selection?
[] Disruptive Selection
[] Directional Selection
[] Stabilizing Selection
[20.6] Selection Acting on Traits Affected by Multiples Genes
What is Disruptive Selection?
[] Disruptive Selection removes/eliminates IMMEDIATE Phenotypes
[20.6] Selection Acting on Traits Affected by Multiples Genes
Give ONE example of a Disruptive Selection and briefly explain it [3]
[] African Black Bellied seed cracker finch
- Heterozygotes reduced in Frequency
- Compared with the Hardy-Weinberg Equilibrium
- When immediate phenotypes are a disadvantaged, a population may exhibit a bimodal trait distribution
[20.6] Selection Acting on Traits Affected by Multiples Genes
What is Directional Selection?
[] Directional Selection is when it eliminates ONE extreme from an array
meaning that;
- it tends to shift the mean value of the population towards the favored end of the distribution
[20.6] Selection Acting on Traits Affected by Multiples Genes
Give ONE example of a Directional Selection
[] Flies (Drosophilia)
- Selected to remove away from light
- Artificial Selection has changed the population in the direction of being less attracted to the light
[20.6] Selection Acting on Traits Affected by Multiples Genes
What is the Stabilizing Selection? + give and Examples
[] It is when it eliminates BOTH extremes from an array of phenotypes which results is to increase it’s frequency of the already common type
- the population may have the same value, but with decreased variation
Birth Weight in Humans-
[20.7] Experimental Studies of Natural Selection
What is it? + give an example.
[] The tested hypothesis that Natural Selection leads to Evolutionary Change can be tested experimentally
- A good example is the “GUPPY [FISH]” color variation in different environment which suggest natural selection at work
[20.7] Experimental Studies of Natural Selection
Explain the differences between the guppies color variation in the ABOVE and BELOW waterfall.
[] It is shown that the guppies above the waterfall has no predators and which are dull guppies
[] And the ones below have predators but are colorful guppies
[20.7] Experimental Studies of Natural Selection
What can we conclude about the ABOVE and BELOW waterfall of guppies?
[] Guppies in natural populations subject to different predators shown to undergo color change over generations
[20.8] Interactions among Evolutionary Forces
List the key TWO factors in this
[] Mutation and Genetic Drift may counter Selection
[] Gene Flow may promote or constrain evolutionary change
[20.8] Interactions among Evolutionary Forces
Briefly explain the “Mutation and Genetic Drift may counter select”
- High rate of mutation could oppose natural selection
- Genetic drift also can work counter to natural selection
[20.8] Interactions among Evolutionary Forces
Briefly explain the “Gene flow may promote or constrain evolutionary change”
- It can spread a beneficial mutation to other populations but it can also impede adaptation due to influx of alleles with low fitness in a populations environment.
[20.9] Limits of Selection
List the THREE limits of Selection
[] Genes have multiple effects
[] Evolution requires genetic variation
[] Gene interactions affect fitness of alleles
[20.9] Limits of Selection
What consists in the “Genes have multiple effects”? + explain it briefly
[] Pleiotropy:
- Multi phenotypic effects of Alleles
- Sets limits on how much a phenotype can be altered
[20.9] Limits of Selection
In regards to the 2nd limit, explain it briefly + give an example
[] Intense selection pressure may remove genetic variation
Example: Increase speed in racehorse
[20.9] Limits of Selection
In regards to “Gene interactions affect fitness of alleles, what is the one factor?
[] Epistasis
- Fitness of ONE allele may vary depending on the genotype of the SECOND genotype
