BSCI222 exam 2 vocab

quantitative genetics

the genetic analysis of complex characteristics

meristic characteristics

characteristic whose phenotype varies in whole numbers, such as a number of vertebrae, but may be caused by continuous genetic variation

threshold characteristic

characteristic that has only two phenotypes (presence and absence) but whose expression depends on an underlying susceptibility that varies continuously

frequency distribution

a concise graphical method of summarizing values. In genetics, the phenotypes found in a group of individuals are usually displayed with the phenotypic classes plotted on the horizontal (x) axis and the numbers/proportions of individuals in each class are plotted on the vertical (y) axis

normal distribution

common type of frequency distribution that exhibits a symmetrical, bell-shaped curve; usually arises when a large number of independent factors contribute to a measured value

heritability

proportion of total phenotypic variation that is due to genetic differences

phenotypic variance (V_P)

measure of the degree of phenotypic difference among a group of individuals; composed of genetic, environmental, and genetic-environmental interaction variances

genetic variance (V_G)

component of phenotypic variance that is due to genetic differences among individual members of a population

environmental variance (V_E)

component of phenotypic variance that is due to environmental differences among individual members of a population

genetic-environmental interaction variance (V_GE)

component of phenotypic variance that results from an interaction between genotype and environment that causes genotypes to be expressed differently in different environments

additive genetic variance (V_A)

component of genetic variance that comprises the additive effects of genes on the phenotype

dominance genetic variance (V_D)

component of genetic variance that can be attributed to dominance (interaction between genes at the same locus)

gene interaction variance (V_I)

component of genetic variance that can be attributed to gene interaction (interaction between genes at different loci)

broad-sense heritability (H²)

proportion of phenotypic variance that can be attributed to genetic variance

narrow-sense heritability (h²)

proportion of phenotypic variance that results from the additive genetic variance

quantitative trait loci (QTL)

a chromosomal region containing genes that control polygenic characteristics

natural selection

differential reproduction of individuals with different genotypes

artificial selection

selection practiced by humans where we promote the reproduction of organisms with the traits perceived as desirable

response to selection

the extent to which a characteristic subjected to selection changes in one generation; equals the selection differential times the narrow-sense heritability

selection differential

difference between the mean phenotype of the selected parents and the mean phenotype of the original population

realized heritability

heritability determined by a response-to-selection experiment

phenotypic correlation

correlation between two or more phenotypes in the same individual

genotypic correlation

phenotypic correlation due to an effect of the same gene or genes on two or more characteristics

genetic rescue

introduction of new genetic variation into an inbred population in an effort to improve the health of the population and better ensure its long-term survival

population genetics

the branch of genetics that studies the genetic makeup of groups of individuals and how a group’s genetic composition changes over time

mendelian population

a group of interbreeding, sexually reproducing individuals that have a common set of genes

gene pool

set of all genes in a population

genotypic frequency

proportion of a particular genotypes within a population

allelic frequencies

proportion of a particular allele within a population

hardy-weinberg law

principle of population genetics stating that if a population is large, randomly mating, and not affected by mutation, migration, or natural selection, then allelic frequencies of a population do not change and the genotypic frequencies stabilize after one generation in the proportions p² (the frequency of AA), 2pq (the frequency of Aa), and q² (the frequency of aa), where p equals the frequency of allele A and q equals the frequency of allele a

hardy-weinberg equalibrium

frequencies of genotypes when the conditions of the hardy-weinberg law are met

positive assortative mating

one type of nonrandom mating where there is a tendency for like individuals to mate

negative assortative mating

one type of nonrandom mating where there is a tendency for unlike individuals to mate

inbreeding

a form of nonrandom mating; preferential mating between related individuals

outcrossing

preferential mating between unrelated individuals

inbreeding coefficient

a measure of inbreeding; the probability (ranging from 0 to 1) that two alleles are identical by descent

inbreeding depression

decreased fitness arising from inbreeding; often due to the increased appearance of lethal or deleterious traits with inbreeding

sampling error

deviations from expected ratios due to chance when the sample size is small

genetic drift

change in allelic frequencies due to a sampling error

effective population size (N_e)

effective number of breeding adults in a population; influenced by the number of individuals contributing genes to the next generation, their sex ratio, variation between individuals in reproductive success, fluctuation in population size, age structure of the population, and whether mating is random

founder effect

sampling error that results from the establishment of a population by a small number of individuals; leads to genetic drift

genetic bottleneck

sampling error that arises when a population undergoes a drastic reduction in size; leads to genetic drift

fixation

when one allele reaches a frequency of 1 in a population, at which point all individuals in the population are homozygous for one allele

fitness (W)

reproductive success of a genotype relative to that of other genotypes in a population

selection coefficient (s)

measure of the relative intensity of selection against a genotype; equals 1 minus W

directional selection

selection in which one allele or trait is favored over another

overdominance

selection in which the heterozygote has a higher fitness than either homozygote; also called heterozygote advantage

underdominance

selection in which the heterozygote has lower fitness than either homozygote

evolution

genetic change that takes place in a group of organisms

anagenesis

evolution taking place within a single lineage

cladogenesis

evolution in which one lineage is split into two

neutral-mutation hypothesis

proposal that much of the molecular variation seen in natural population is adaptively neutral and unaffected by natural selection; that is, that individuals with different molecular variants have equal fitness

balancing selection

natural selection that maintains genetic variation

species

term applied to different kinds or types of living organisms

biological species concept

definition of a species as a group of organisms whose members are capable of interbreeding with one another but are reproductively isolated from the members of other species. Because different species do not exchange genes, each species evolved independently. not all biologists adhere to this concept.

reproductive isolating mechanism

any biological factor or mechanism that prevents gene exchange

prezygotic reproductive isolating mechanism

reproductive isolating mechanism that prevents gametes from two different species from fusing and forming a hybrid zygote

ecological isolation

reproductive isolation in which different species live in different habitats and interact with the environment in different ways, so that their members do not encounter one another and do not reproduce with one another

behavioral isolation

reproductive isolation due to differences in behavior that prevent interbreeding

temporal isolation

reproductive isolation in which the reproduction of different species takes place at different times of the year; exemplified by some species of plants that do not exchange genes because they flower at different times of the year

mechanical isolation

reproductive isolation resulting from anatomical differences that prevent successful exchange of gametes

gametic isolation

reproductive isolation due to the incompatibility of gametes. mating between members of different species may take place, but the gametes do not form zygotes. see in many plants in which pollen from one species cannot fertilize the ovules of other species.

postzygotic reproductive isolating mechanisms

reproductive isolating mechanisms that operates after gametes from two different species have fused to form a zygote, either because the resulting hybrids are inviable of sterile or because reproduction breaks down in subsequent generations

hybrid inviability

reproductive isolating mechanism in which mating between two organisms of different species takes place and hybrid offspring are produced, but the resulting embryos are not viable

hybrid sterility

reproductive isolating mechanism in which hybrid embryos complete development but are sterile; exemplified by mating between donkeys and horses to produce a mule, a viable but usually sterile offspring

hybrid breakdown

reproductive isolating mechanism in which closely related species are capable of mating and producing viable and fertile F₁ progeny, but genes do not flow between the two species because further crossing of the hybrids produces inviable or sterile offspring

speciation

process by which new species arise; comes about through the evolution of reproductive isolating mechanisms

allopatric speciation

speciation that occurs when a geographic barrier splits a population into two groups and blocks the exchange of genes between them

sympatric speciation

speciation that arises in the absence of any geographical barrier to gene flow, in which reproductive isolating mechanisms evolve within a single population

phylogeny

evolutionary relationships among a group of organisms

phylogenetic tree

graphical representation of the evolutionary relationships among different organisms

branch

an evolutionary connected between nodes in a phylogenetic tree representing an evolutionary connection between organisms

node

point in a phylogenetic tree where branches split; represents a common ancestor

rooted tree

phylogenetic tree in which one node represents a common ancestor to all other organisms (nodes) on the tree; all the organisms depicted have a common ancestor

gene tree

phylogenetic tree representing the evolutionary relationships among organismks or DNA sequences

molecular clock

use of molecular differences to estimate the time of evolutionary divergence between organisms; assumes a roughly constant rate at which one neutral mutation replaces another

exon shuffling

process by which exons of different genes are exchanged, creating genes that are mosaics of other genes; has been important in the evolution of eukaryotic genes

multigene family

set of genes similar in sequence that arose through repeated duplication events and often encode different protein products

prototrophic

capable of using a carbon source, essential elements such as nitrogen and phosphorus, certain vitamins, and other required ions and nutrients to synthesize all the compounds needed for growth and reproduction

minimal medium

medium that contains the nutrients required by only prototrophic bacteria- typically a carbon source, essential elements such as nitrogen and phosphorus, certain vitamins, and other required ions and nutrients

auxotrophic

possessing a nutritional mutation that disrupts the ability to synthesize an essential biological molecule; this bacterium cannot grow on a minimal medium but can grow on a minimal medium to which has been added the biological molecule that it cannot synthesize

complete medium

a medium that contains all the substances required y bacteria for growth and reproduction

colony

clump of genetically identical bacteria derived from a single bacterial cell that undergoes repeated rounds of division

plasmid

small, usually circular DNA molecule that is distinct from a bacterial chromosome; capable of replicating independently of the bacterial chromosome

episome

plasmid capable of replicating freely and able to integrate into a bacterial chromosome

F (fertility) factor

episome of E. coli that controls conjugation and gene exchange between E. coli cells; contains an origin of replication and genes that enable to bacterium to undergo conjugation

conjugation

mechanism by which genetic material can be transferred from one bacterium to another; in the process, two bacteria lie together, and a connection forms between them. A plasmid, or sometimes part of the bacterial chromosome, passes through this connection from one cell to the other

transformation

mechanism by which DNA found in the environment is taken up by a cell. after this process, recombination may take place between the introduced genes and those of the bacterial chromosome

transduction

type of gene exchange that takes place when a virus carries genes from one bacterium to another. After it is inside the cell, the newly introduced DNA may undergo recombination with the bacterial chromosome

pilus (pili)

extension of the cell membrane of some bacteria that allows conjugation to take place. When this area of the cell makes contact with a receptor on another cell, it contracts and pulls the two cell together

human microbiome

the community of bacteria associated with humans

competence

the ability to take up DNA from the environment (to be transformed)

transformant

cell that has received genetic material through transformation

cotransformation

process in which two or more genes are taken up together during cell transformation

horizontal gene transfer

transfer of genes from one organism to another by a mechanism other than reproduction

restriction-modification system

a type of bacterial defense that uses restriction enzymes to cleave foreign DNA. The bacteria protects its own DNA from cleavage by modifying the sequences recognized by the restriction enzymes

CRISPR-Cas system

a system used by bacteria and archaea as a defense against foreign DNA. Has been adapted for use as a molecular tool for precisely cutting DNA, providing a powerful way of editing the genome.

CRISPR array

a series of repeated DNA sequences called clustered regularly interspaced short palindromic repeated located in the bacterial or archaeal chromosome. Fragments of foreign DNA are inserted into the array and are later transcribed into CRISPR RNA

Cas proteins

proteins that function in the CRISPR-Cas systems. Combine with cRNA to form an effector complex that cleaves DNA at specific base sequences