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Allele frequencies

Allele frequencies

rates of occurrence of alleles in populations

Fixed

when a population exhibits only one allele at a particular gene

Fitness

a measure of the extent to which the individual's genotype is represented in the next generation

Heritability

in the population, the proportion of the total variation in a trait that is due to genetic differences among individuals

Stabilizing selection

maintains the status quo and acts against extremes

Directional selection

leads to a change in a trait over time, favors one extreme of a trait

Disruptive selection

operates in favor of extremes and against intermediate forms, selecting against the mean

Gene pool

all the alleles present in all individuals in a population or species

Gene flow

homogenized allele frequencies between two populations

Assumptions of HW

1: No differences in the survival and reproductive success of individuals 2: No migration 3: No mutations 4: Must be sufficiently large population size 5: Must be random mating

Variation

Mutation generates new variation; Recombination followed by segregation of homologous chromosomes during meiotic cell division shuffles mutations to create new combinations

Random mating

mate choice must be made without regard to genotype

Inbreeding

mating occurs between close relatives; Increases frequency of homozygote and decreases the # of heterozygotes without affecting allele frequencies

Inbreeding depression

a reduction in the child's fitness caused by homozygosity of deleterious recessive mutations

Genetic drift

a change in the frequency of an allele due to the random effects of limited population size

Migration

reduces genetic variation between populations; \n Results in gene flow: the movement of alleles from one population to another

Mutation

increases genetic variation

Founder effect

a type of bottleneck that occurs when only a few individuals establish a new population

Non-random mating

individuals mate based on genotype; alters genotype frequencies without affecting allele frequencies

Kin selection

a form of natural selection that favors the spread of alleles that promote behaviors that help close relatives, or kin

Altruism

behavior that benefits another individual at a cost to the altruist's personal fitness (ability to produce offspring)

Reciprocal altruism

individuals exchange favors; Individuals must be able to recognize one another and remember previous interactions

Direct fitness

the number of offspring an individual produces

Indirect fitness

the number of relatives produced multiplied by the degree of relatedness to those individuals

Sexual selection

promotes traits that increase an individual's access to reproductive opportunities

Natural selection

a process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits

Sexual selection

A form of selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates; often powerful enough to produce features that are harmful to the individual's survival

Hamilton's Rule

Being related to individuals and how this impacts your fitness; \n rB > C; As long as rB exceeds C, altruism can evolve

Adaptive traits

a genetic trait that helps an organism to maximize its reproductive success; enhance individual survival and reproduction of individuals in a population

Non-adaptive trait

not affected by fitness

Biological species concept

species is a group of actually or potentially interbreeding populations whose members can produce viable, fertile offspring and that are reproductively isolated from other species

Morphospecies concept

the idea that members of the same species usually look like each other more than like other species; Relies on phenotype and morphology

Ecological species concept

concept that there is a one-to-one correspondence between a species and its niche

Phylogenetic species concept

concept that members of a species all share a common ancestry and a common fate

Speciation

the development of reproductive isolation between populations

genetic divergence

Low hybridization rate between 2 species; Low gene flow; Nonrandom mating

Allopatric speciation

results from the geographical separation of populations

allopatric populations

populations that are geographically separated from each other

Dispersal

the process in which some individuals colonize a distant place far from the main source population

Peripatric speciation

specific kind of allopatric speciation in which a few individuals from a mainland population disperse to a new location remote from the original population and evolve separately

Vicariance

process in which a geographic barrier arises within a single population, separating it into two or more isolated populations

Co-speciation

a process in which two groups of organisms speciate in response to each other and at the same time, producing matching phylogenies

Sympatric speciation

takes place in single geographic area; Gene flow may be prevented by polyploidy or by habitat specialization

Instantaneous speciation

caused by hybridization between two species in which the offspring are reproductively isolated from both parents

Species

group of individuals that can exchange genetic material through interbreeding to produce fertile offspring

Population

a group of individuals of the same species living in the same place at the same time that can interbreed

Molecular clock

correlation between the time two species have been evolutionarily separated and the amount of genetic divergence between them

Pre-zygotic isolating factors

prevent fertilization from taking place

Post-zygotic factors

occur after fertilization; factors that cause the failure of the fertilized egg to develop into a fertile individual.

Reinforcement

process by which diverging populations undergo natural selection in favor of traits that enhance pre-zygotic isolation, thereby preventing the production of less fit hybrid offspring; Selection against individuals who have hybrid offspring

Phylogenies

are hypotheses because they represent the best model, or explanation, of the relatedness of organisms based on all the existing data

Homologous

characters that are similar because of descent from a common ancestor

Analogous

similarities due to independent adaption by difference species; Result of convergent evolution

Parsimony

assumption that the fewest evolutionary steps is the most likely explanation

Convergent evolution

process whereby organisms not closely related (not monophyletic) independently evolve similar traits as a result of having to adapt to similar environments or ecological niches

Synapomorphy

a shared derived character

Homoplasy

a character shared by a set of species but not present in their common ancestor

Node

the point where a branch splits, representing the common ancestor from which the descendant species diverge

Sister taxa/ groups

groups that are more closely related to each other than either of them is to any other group

Monophyletic group

all members share a single common ancestor not shared with any other species or group of species

Paraphyletic group

groupings that include some, but not all, the descendants of a common ancestor

Phylogenetic tree

a diagrammed hypothesis about the evolutionary history, or phylogeny, of a species

Cancer

cell growth disorder resulting from an alteration in genes (mutations) that lead to unregulated cell growth

Proto-oncogene

can cause cancer only when mutated.

Tumor suppressor

genes that encode proteins whose normal activities inhibit cell division

Rb protein

a transcriptional repressor that inhibits the transcription activator E2F

Germline mutation

a mutation that occurs in a reproductive cell or a cell that develops into the reproductive cell and are therefore passed on to the next generation

Germ cells

reproductive cells that produce sperm or eggs and the cells that give rise to them

Gamete

a mature haploid male or female germ cell that is able to unite with another of the opposite sex in sexual reproduction to form a zygote

Somatic mutation

occurs in somatic cells and only affect the individual in which they occur and are not transmitted to offspring

Somatic cell

a non-reproductive cell

The Law of Segregation

Individuals inherit two copies of each gene, one from the mother and one from the father, and when the individual forms reproductive cells, the two copies separate equally; One parent transmits one member of a pair to an offspring; therefore they segregate; A progeny gets one factor from its mom and one from its father and thus a pair of factors

The Law of Independent Assortment

Segregation of one set of alleles of a gene pair is independent of the segregation of another set of alleles of a different gene pair

Allele

different forms of a gene, corresponding to different DNA sequences in each different form

Genotype

the genetic makeup of a cell or organism; the particular combination of alleles present (AA, Aa, aa, etc)

Phenotype

observable traits or characteristics (tall, short, round)

Product rule

The principle that the probability of two independent events occurring together is the product of their respective probabilities; Outcomes can occur simultaneously (and)

Sum rule

The principle that the probability of either of two mutually exclusive outcomes occurring is given by the sum of their individual probabilities; Outcomes being considered cannot occur simultaneously (or)

Incomplete dominance

phenotype of the heterozygous genotype is intermediate between homozygous parents; Neither allele is dominant or recessive to the other, intermediate is created

Co-dominance

phenotypes of both alleles are observed in the heterozygotes; Both characteristics shown at the same time, not an intermediate

Epistasis

one gene interferes with or masks another gene

homologous recombination

Homologous chromosomes replicate, then pair; Allows any pair of parental genomes to form infinite # of recombinant gametes, depending on where crossover occurs along the chromosomes

Linked

genes that are sufficiently close together in the same chromosome that they do not assort independently

Recombination

the exchange of genes between chromosomes, resulting in a different genetic combination and ultimately the formation of unique gametes with chromosomes that are different from those in parents

Recombinants

An offspring with a different combination of alleles from that of either parent, resulting from one or more crossovers in prophase I of meiosis; There will always be more parental than recombinants

Recombination frequency

(# of recombinants/ total # of progeny) \n Depends on the distance between the genes; The closer genes are along the chromosome, the less likely it is that a crossover will take place in the interval between them (father apart genes = higher recombination frequency)

Meiosis

Happens in germ cells; Generates unique gametes; Diploid cells make haploid cells, which become diploid again after sexual reproduction

Meiosis I

Chromosome duplication; Chromosomes align with homologous chromosomes facing opposite poles: Homologous chromosomes separate move to opposite poles

Chromosome duplication

DNA is replicated in S phase and the chromosome duplicates; is now comprised of sister chromatids; Each chromosome has 2 chromatids

Meiosis II

Chromosomes align with sister chromatids facing opposite poles; Sister chromatids separate and move to opposite poles

Independent assortment of genes on different chromosomes

results from the mechanics of meiosis, in which different pairs of homologous chromosomes align randomly on the metaphase plate in meiosis I. For some pairs of chromosomes, the maternal chromosome goes toward one pole during anaphase I, and the paternal chromosome goes to the other pole, but for other pairs, just the opposite occurs. Because the alignment is random, gene pairs on different chromosomes assort independently of one another

Non- disjunction

the failure of a pair of chromosomes to separate normally during anaphase of cell division; One daughter cell receives extra copy of chromosome while other receives no copy; Violates principle of segregation

Restriction enzymes

cleave double-stranded DNA at specific sequences known as restriction sites; useful in DNA fingerprinting because DNA from different individuals can differ in the distance between adjacent restriction sites or in the presence or absence of a particular restriction site at some location in the genome

Background extinction

the standard rate of extinction in earth's geological and biological history before humans became a primary contributor to extinctions.

Latitudinal diversity gradient

higher species diversity at the equator; Higher productivity = more things can be supported in higher trophic levels

biotic interactions

Interactions among organisms

abiotic interactions

Interactions between organism and their non-living environments

Population

group of individuals of the same species that live interact and interbreed in a particular area at the same time

Community

assemblage of interacting populations of different species in a particular area

Ecosystem

a community of organisms and the physical environment it occupies