Ch. 26 Flashcards
A gene pool is..
All of the genes in a population of individuals
In natural populations, most genes are..
Polymorphic
A gene exists in two alleles designated D and d. If 48 copies of this gene are the D allele and 152 are the d allele, what is the allele frequency of D?
Total = 200 40/200 = .24
The allele frequency of C is 0.4 and c is 0.6. If the population is in Hardy-Weinberg equilibrium, what is the frequency of heterozygotes?
2pq = 2(0.6)(0.4) = .48
Which of the following is a factor that does NOT promote widespread changes in allele or genotype frequencies? A) new mutations B) natural selection C) genetic drift D) migration E) nonrandom mating
A) New mutations
Darwinian fitness is a measure of..
Reproductive success
Within a particular population, darkly colored rats are more likely to survive than more lightly colored individuals. This scenario is likely to result in ___ ___.
Directional selection
A population occupies a diverse environment in which the fitness of some genotypes is higher in one environment while the fitness of other individuals is higher in another environment. This scenario is likely to result in ___ ___.
Disruptive selection
A gene exists in two alleles, and the heterozygote has the highest fitness. This scenario is likely to result in ___ ___.
Balancing selection
What does the term “local population” mean?
A local population is a group of individuals that are more likely to interbreed with each other compared with more distant populations
Are polymorphisms common or rare in natural populations?
Polymorphisms are very common in nearly all natural populations
Directional selection
In this form of natural selection, explain the meaning of the word “directional.”
The word “directional” means that selection is favoring a particular phenotype.
Selection is moving the population in the direction in which that phenotype will predominate.
Directional selection for DDT resistance in a mosquito population.
In this example, is directional selection promoting genetic diversity? Explain.
No, because directional selection is eliminating individuals that are sensitive to DDT.
The geographic relationship between malaria and the frequency of the sickle cell allele in human populations.
Explain why the Hb^5 allele is prevalent in certain regions even though it is detrimental in the homozygous condition.
The Hb^5 allele is an advantage in the heterozygous condition because it confers resistance to malaria. The heterozygote advantage outweighs the homozygote disadvantage.
Explain how negative frequency-dependent selection works.
In negative frequency-dependent selection, the rarer phenotype has a higher fitness, which improves its reproductive success.
Disruptive selection.
Does this form of natural selection favor polymorphism? Explain why or why not.
Yes, this selection favors polymorphism. The fitness values of phenotypes depend on the environment. Some phenotypes are the fittest in one environment whereas other phenotypes are the fittest in another environment.
Stabilizing selection.
In general, why does stabilizing selection decrease genetic diversity?
Stabilizing selection decreases genetic diversity because it eliminates individuals that carry alleles that promote more extreme phenotypes.
The central issue in ___ ___ is genetic variation.
Population genetics
Population genetics
It’s foundations are largely attributed to 3 mathematicians:
- sir Ronald fisher
- sewall wright
- J. B. S. Haldane
All of the alleles of every gene in a population make up the ___ ___.
Gene pool
The focus is shifted away from the individual and toward..
The population of which the individual is a member
Only individuals that ___ contribute to the gene pool of the next generation.
Reproduce
Population geneticists study..
The genetic variation within the gene pool and how it changes from one generation to the next
A ___ is a group of individuals of the same species that occupy the same region and can interbreed with each other.
Population
A large population is usually composed of smaller groups called ___ ___, or “___.”
Local populations, demes
Local populations are often separated from each other by moderate ___ ___.
Geographic barriers
A population may change in:
- size
- geographic location
- genetic composition
The term ___ refers to the observation that many traits display variation within a population with the gene existing as two or more allele.
Polymorphism
At the DNA level, polymorphism is due to..
Two or more alleles that influence the phenotype
“___” is also used to describe a gene that commonly exists as 2 or more alleles in a population.
Polymorphic
A ___ gene exists predominately as a single allele.
Monomorphic
Variation can even be as small as ___ ___ ___.
Single-nucleotide polymorphism (SNP)
Allele frequency=
of copies of an allele in a population/ total # of all alleles for that gene in a population
Genotypes frequency=
of individuals with a particular genotype in a population / total # of individuals in a population
The HW equation is also called an ___.
Equilibrium
The HW equation provides a quantitative relationship between the ___ and ___ ___.
Alleles and genotype frequencies
If the chi square is too high, we would say the population is in ___.
Disequilibrium
___ describes changes in a populations gene pool from generation to generation.
Microevolution
