Population Genetics Flashcards
__________________ can cause
changes in allele frequency.
Selection, migration, and genetic drift
_______ creates new alleles in a population gene pool.
Mutation
_______ changes population genotype frequency but not allele frequency.
Nonrandom mating
source of variation
mutation and recombination
mechanism of inheritance
segregation of alleles
a consequence of changes in genetic material through mutation and changes in allele frequencies in populations over time
Evolution
union of population genetics with the theory of natural selection
neo-Darwinism
the formation of new species
speciation
Sources of speciation
Natural selection
Mutation
Migration
Drift
______investigate patterns of genetic variation within and among groups of interbreeding individuals
Population geneticists
evolutionary change within populations of a species
Changes in allele frequencies in a population that do not directly result in species formation
microevolution
evolutionary events leading to the emergence of new species and other taxonomic groups
macroevolution
is a group of individuals belonging to the same species that live in a defined geographic area and actually or potentially interbreed
population
The genetic information carried by members of a population constitutes that population’s _____
gene pool
_________ , which ran from 2008 through 2015, was a global effort to identify and catalog at least 95% of the common genetic variations carried by the 7 billion people now inhabiting the planet.
1000 Genomes Project
The 1000 Genomes Project eventually sequenced the genomes of 2504 individuals from 26 populations using a combination of _____
- whole-genome sequencing at low coverage levels
- exome sequencing
- microarray genotyping.
mutations leading to amino acid substitutions are usually detrimental, with only a very small fraction being favorable
neutral theory of molecular evolution
Some mutations are neutral; that is, they are functionally equivalent to the allele they replace
Mutations that are favorable or detrimental are preserved or removed from the population, respectively, by natural selection. However, the frequency of the neutral alleles in a population will be determined by mutation rates and random genetic drift, and not by selection.
The neutral theory nonetheless serves a crucial
function:
It points out that some genetic variation is expected simply as a result of mutation and drift.
describes what happens to allele and genotype frequencies in an “ideal” population that is infinitely large and randomly mating and that is not subject to any evolutionary forces such as mutation, migration, or selection
model that shows the relationship between the relative proportions of alleles in the gene pool and the frequencies of different genotypes in the population
Hardy–Weinberg law
the distribution of genotypes among the zygotes is…
p^2 + 2pq + q^2 = 1
two main predictions of the Hardy-Weinberg model:
- Allele frequencies in our population do not change from one generation to the next.
- After one generation of random mating, genotype frequencies can be predicted from the allele frequencies.
The theoretical population described by the Hardy–Weinberg model is based on the following assumptions:
- Equal survival rates of offspring.
- Absence of selection and mutation.
- Lack of migration.
- Large population size.
- Random mating.
Hardy–Weinberg model can be used to identify the real-world forces that cause allele frequencies to change
The Hardy–Weinberg model has three additional important consequences:
- Dominant traits do not necessarily increase from one generation to the next.
- Genetic variability can be maintained in a population, since, once established in an ideal population, allele frequencies remain unchanged.
- Under Hardy–Weinberg assumptions, knowing the frequency of just one genotype enables us to calculate the frequencies of all other genotypes at that locus.
A small number of individuals who make high-risk choices (such as having unprotected sex with HIV positive partners) never become infected. Some of these individuals are homozygous for a mutant allele of a gene called _______
CCR5 - encodes a protein called the C-C chemokine receptor-5 (CCR5)
______ are cell surface signaling molecules associated with the immune system.
Chemokines
in which chromosome is CCR5 gene found
Chromosome 3
how does the HIV-1 infection resistance in CCR5 gene
32-bp deletion in exon 4 that confers resistance to HIv-1 infection
Hardy-Weinberg formula for 3 alleles
p^2 + q^2 + r^2 + 2pq + 2pr + 2qr = 1
_______ occurs whenever individuals with a particular genotype enjoy an advantage in survival or reproduction over other genotypes
Selection
An individual organism’s genetic contribution to future generations is called its _____
fitness (𝑤)
Types of Selection
- Directional
- Stabilizing
- Disruptive
traits at one end of a spectrum of phenotypes present in the population become selected for or against, usually as a result of changes in the environment.
directional selection
selects for intermediate phenotypes, with those at both extremes being selected against. Over time, this will reduce the phenotypic variance in the population but without a significant shift in the mean.
Stabilizing selection
is selection against intermediate phenotypes and selection for phenotypes at both extremes
Disruptive selection
A reduction in gene flow between populations, accompanied by selection or genetic drift, can lead to reproductive isolation and speciation.
assortment and recombination do not produce new alleles.
Mutation - Creates new alleles but has a slow impact on allele frequencies unless the population is small.
mutation rate m for achondroplasia
μ = 1.4 x 10^-5 +- 0.5 x 10^-5
occurs when individuals move between populations
migration
In small populations, significant random fluctuations in allele frequencies are possible by chance alone, a situation known as ______
genetic drift
occurs when a population originates from a small
number of individuals
founder effect
develop when a large population undergoes a drastic but temporary reduction in numbers
Genetic bottleneck
_________, similar genotypes are more likely to mate than dissimilar ones.
positive assortative mating
______ occurs when dissimilar genotypes are more likely to mate
Negative assortative mating
______ occurs when mating individuals are more closely related than any two individuals drawn from the population at random; loosely defined, it is mating among relatives.
Inbreeding
This coefficient quantifies the probability that the two alleles of a given gene present in an individual are identical because they are descended from the same single copy of the allele in an ancestor.
coefficient of inbreeding (F)
If F = 1, all individuals in the population are homozygous, and both alleles in every individual are derived from the same ancestral copy. If F = 0, no individual has two alleles derived from a common ancestral copy.
As the level of inbreeding increases, the frequency of heterozygotes declines.
a group of actually or potentially interbreeding organisms that is reproductively isolated in nature from all other such groups.
Species
a period with no change
stasis
an evolutionary process where a species evolves gradually while continuing to exist as an interbreeding population
Anagenesis
an evolutionary process where a parent species splits into two or more descendant species, forming a clade
Cladogenesis
The biological barriers that prevent or reduce interbreeding between populations are called…
reproductive isolating mechanisms
reproductive isolating mechanisms
- Geographic or ecological - The populations live in the same regions but occupy different habitats.
- Behavioral - (Only in animals.) The populations are isolated by different and incompatible behavior before mating.
- Seasonal or temporal - The populations live in the same regions but are sexually mature at different times.
- Mechanical - Cross-fertilization is prevented or restricted by differences in reproductive structures
- Physiological - Gametes fail to survive in alien reproductive tracts.
________ prevent individuals from mating in the first place.
Prezygotic isolating mechanisms
_____ create reproductive isolation even when the members of two populations are willing and able to mate with each other
Postzygotic isolating mechanisms
In animal evolution, one of the most effective prezygotic mechanisms is ______, involving courtship behavior.
behavioral isolation
Postzygotic Mechanisms: Fertilization takes place and hybrid zygotes are formed, but these are nonviable or give rise to weak or sterile hybrids.
- Hybrid nonviability or weakness.
- Developmental hybrid sterility. Hybrids are sterile because gonads develop abnormally or meiosis breaks down before completion.
- Segregational hybrid sterility. Hybrids are sterile because of abnormal segregation into gametes of whole chromosomes, chromosome segments, or combinations of genes.
the average time for speciation ranges from _____ years
100,000 to 10,000,000 years
(of a group of organisms) descended from a common evolutionary ancestor or ancestral group
monophyletic
show the ancestral relationships among a group of organisms
branches represent the relationships among lineages over time.
The length of a branch can be derived from a time scale.
Nodes, show when a species split into two or more species. Each node represents a common ancestor of the species diverging at that node.
The root of a phylogenetic tree represents the oldest common ancestor to all the groups shown in the tree.
Phylogenetic trees
Groups that consist of an ancestral species and all its descendants are called ______
monophyletic groups
Constructing a species-level phylogenetic tree using DNA sequences involves three steps:
- DNA sequences representing a gene or genome of interest from a number of different species must be acquired. - available from public databases
- The sequences must be aligned with each other so that the related parts of each sequence can be compared to see if they are the same or different - can be imported into software programs that maximize the number of aligned base pairs by inserting gaps as needed
- These DNA differences are used to construct a phylogenetic tree, often beginning with the most closely related sequences and working backward through sequences that are less closely related
the closest living relative to terrestrial vertebrates, _______
lungfish
use the rate of change in amino acid or nucleotide sequences as a way to estimate the time of divergence from a common ancestor.
molecular clocks
the study of ancient DNA to reconstruct and analyze the genomes of organisms that are no longer alive
paleogenomics
________________—a species that became
the ancestor to our species
H. heidelbergensis
out-of-Africa hypothesis
- H. sapiens evolved from the descendants of H. heidelbergensis in Africa about 300,000 years ago.
the group of cells in a multicellular organism that develop into germ cells
germline
branch of genetics which deals with the behavior of genes at the population level
the study of polymorphism and divergence
population genetics
multiple forms of a trait within a species
polymorphism
local interbreeding units; also called local
populations, Mendelian populations or demes
subpopulation
Number of times an allele occurs in a gene pool, compared to the total number of alleles for that gene
Allele frequency
Populations, not individuals, evolve
Why is genetic variation important?
it allows populations to adapt and survive in changing environments and it’s the raw material for evolution
How does genetic structure change?
Mutation
Genetic drift
Gene flow (migration)
Nonrandom mating
Natural selection
Mdh-1alleles in snail colonies
Malate dehydrogenase (enzyme crucial for energy production in cells)
Krebs cycle
Lap locus in prairie vole populations
encodes the enzyme leucine aminopeptidase, plays a significant role in protein metabolism
adaptation to environmental chang
conervation
divergence of populations
biodiversity
Mechanisms of variation
Mutation
Sexual reproduction
Gene flow
Mechanisms of change
Genetic drift
Natural selection
different molecular forms of an enzyme that correspond to different alleles of a common gene (locus)
Allozyme
Signaling molecules used by the immune system
Chemokines
Virus that attacks cells that help the body fight infection
HIV
Gene pool equation
p + q = 1
Genetic change by chance alone
Genetic drift
All individuals are potential partners for reproduction and mating occurs randomly
Panmictic population
