Chapter 19 Flashcards
(50 cards)
Nature selects particular individuals. Acts on individuals but ONLY populations evolve
natural selection
group of members of the same species
population
The sum of all alleles in a population
gene pool
Hardy Weinberg allele equation:
p+q=1
Hardy Weinberg genotypes equation:
p^2 +2pq+q^2=1
p in Allele Weinberg equations stand for what?
dominant allele (p=A)
q in Allele Weinberg equations stand for what?
recessive allele (q=a)
p^2 in Genotypes equation stands for what?
homozygous dominant (AA)
2pq in Genotypes equation stands for what?
heterozygous (Aa)
q^2 in Genotypes equation stands for what?
homozygous recessive (aa)
Answer the equation for the Allele Weinberg equation:
What does q equal?
p=A= .9
q=???
What about finding p?
p=???
q= 0.2
q(a)= .1, p(A)= 0.8
New alleles arise by this, a change in the nucleotide sequence of DNA. Only these in cells that produce gametes can be passed to offspring.
mutation
A change of a single nucleotide in a DNA sequence.
“point mutation”
The rate at which a specific allele appears within a population. ex.)ABO Blood
Allele frequency
3 main mechanisms cause allele frequency change:
- Natural Selection
- Genetic Drift
- Gene Flow
A population’s individuals often display different phenotypes, or express different alleles of a particular gene, which is referred to as this.
polymorphisms
Populations with 2 or more variations of a particular characteristic
polymorphic
The fraction of phenotype variation that we can attribute to genetic differences, or genetic variability, among individuals in a population. The greater this is of a population phenotypic variation, the more susceptible it is to the evolutionary forces that act on heritable variation.
Heritability
The diversity of alleles and genotypes within a population. When scientists are involved in the interbreeding of species, such as with animals in zoos and nature preserves, they try to increase this variability to preserve as much as the phenotypic diversity as possible. This also reduces associated risks of interbreeding.
genetic variability
the mating of closely related individuals, which can have the undesirable effect of bringing together deleterious recessive mutations that can cause abnormalities and susceptibility to disease.
interbreeding
What are the 5 things involved in natural selection:
1.) Directional Selection
2.) Disruptive Selection
3.) Stabilizing Selection
4.) Balancing Selection
5.) Sexual Selection
a.) intrasexual selection
b.) intersexual selection
What are the 2 things apart of Genetic Drift?
1.) founder effect
2.) bottleneck effect
Choose individuals at 1 end of the phenotypic range are selected.
far left o far right. Selects for phenotypes at one end of the spectrum of existing variation. When environment changes, population will undergo this. Th result of this type of selection is a shift in population genetic variability, towards the new, fit phenotype.
ex.) begins far left when there are more tan mice. However, dark brown coloration arises by a new mutation. Dark brown fur makes the mouse less susceptible to predation. The population of dark mice has a higher mean fitness than the starting population of tan mice and so have a higher chance of survival and ability to grow and reproduce, so, now the population is skewed to the far right due to this form of selection.
ex.) Peppered moth. Prior to Industrial Evolution, the moths were light in color, which allowed them to blend in with light-colored trees and lichens in their environment. However, as soot began spewing from factories, the trees darkened and so did the moths. Light-colored moths became easier to spot by predatory birds. Overtime, darker moths form increased and then had a higher survival rate in habitats with air pollution because they blended in.
Directional Selection
Chosen are 2 or more phenotypes. 2 or more distinct phenotypes can each have their advantages for natural selection, while the intermediate phenotypes are, on average, less fit. Occurs when conditions favor individuals at both extremes of the phenotypic range.
Ex.) Large, dominant alpha males use brute force to obtain mates, while small males can sneak in for furtive copulations with the females in an alpha male’s territory. In this case, both the alpha males and the “sneaking” males will be selected for, but medium-sized males, who can’t overtake the alpha males and are too big to sneak copulations, are selected against.
Ex.) Imagine a mouse population living at the beach where there is light-colored sand interspersed with patches of tall grass. In this scenario, light-colored mice that blend in with the sand would be favored, as well as dark-colored mice that can hide in the grass. Medium-colored mice, alternatively would not blend in with either the grass or the sand, and thus predators would most likely eat them. The result of this type of selection is increased genetic variability as the population becomes more diverse.
Disruptive Selection
