BIO 365 Exam 2

Polymorphism

Polymorphism

The occurrence of different forms among the members of a population; can be morphological, genetic, behavioral, physiological, etc.

Genotype

The genetic constitution of an individual organism

Phenotype

The expression of the genotype of an organism; may be influenced or even determined by the environmental conditions experienced by the organism.

Mutation

The process of alteration of a gene or chromosome and its product

Purines

The base pairs adenine (A) and guanine (G)

Pyrimidines

The base pairs thymine (T) and cytosine (C)

Chromosome

A single long coiled molecule of DNA

Gene

A sequence of DNA that is transcribed into RNA

Transcription

The process by which DNA is converted to RNA

Translation

The process by which RNA is converted to protein

Locus

A site on a chromosome occupied by a particular gene or base pair region

Exons

Gene segments that code for a protein

Introns

Noncoding DNA segments that occur between the exons

Codon

A 3 bp segment of RNA that codes for a particular protein

Amino acids

The building blocks of proteins that are linked together to form a polypeptide; coded for by RNA.

Allele

Different forms of a gene

Haplotype

A particular DNA sequence that differs by one or more mutations from homologous sequences

Genetic markers

Detectable mutations that geneticists use to recognize specific regions of chromosomes or genes

Fixed

A mutation that has increased in frequency to the point that it is found in every individual (or nearly so) in a population.

Wild type

Fixed genes reflecting the typical genotype or phenotype of a population

Base pair substitution

A mutation that maps to a single locus (often restricted to a single base pair).

Transition

A type of base pair substitution whereby a purine is substituted for a purine (G →A or A → G) or a pyrimidine for a pyrimidine (T → C or C → T)

Transversion

A type of base pair substitution whereby a purine is substituted for a pyrimidine or vice versa

Synonymous mutations

Mutations that have no effect on the resulting amino acid, polypeptide, or protein.

Nonsynonymous mutations

Mutations that result in amino acid substitutions thereby changing (or at least potentially changing) the structure and function of the resulting protein.

dN/dS ratio

The number of nonsynonymous mutations divided by the number of synonymous mutations

dN/dS ratio <1

most nonsynonymous mutations are deleterious and removed by purifying selection,

dN/dS ratio =1

the mutations are evolving neutrally,

dN/dS ratio >1

many of the nonsynonymous mutations were fixed by positive selection

Frameshift mutations

A mutation that causes a shift in the reading frame such that the identities of amino acids occurring downstream of the mutation may be changed; the resulting polypeptide is usually greatly altered

Insertion

A mutation whereby a single base pair is inserted into a DNA sequence

Deletion

A mutation whereby a single base pair is deleted from a DNA sequence

Recombination or crossing over

A normal process where genes are exchanged between chromosomes during meiosis

Unequal crossing over

When two chromosomes are not perfectly aligned; results in tandem duplication on one chromosome and deletion on the other

Pleiotropy

Occurs when multiple phenotypic traits are affected by a single mutation

Karyotype

A description of the complement of chromosomes that includes number, size, shape, and internal arrangement.

Aneuploidy

Unbalanced chromosome complement; usually results in inviability or poor development

Polyploidy

Changes in the number of whole sets of chromosomes

Diploid

An organism with two entire sets of chromosomes (2N)

Polyploid

An organism with more than two sets of chromosomes (3N, 4N, 5N, etc.)

Phenotypic plasticity

The capacity of an organism of a given genotype to express different phenotypes under different environmental conditions

Norm of reaction

The variety of different phenotypic states that can be produced by a single genotype under different environmental conditions

Genotype x environment interaction

The effect of environmental differences on a phenotype differs among genotypes.

Allele frequency

The relative commonness (or rarity) of an allele in a population

Homozygotes

In sexually reproducing, diploid organisms that carry two copies of the same allele

Heterozygotes

In sexually reproducing, diploid organisms that carry a copy of two different alleles

Genotype frequency

The proportion of a population that has a certain genotype

Hardy-Weinberg principle

Whatever the initial genotype frequencies for two alleles may be, after one generation, the genotype frequencies will be p2: 2pq: q2

Hardy-Weinberg equilibrium

When genotypes have the frequencies predicted by the Hardy-Weinberg principle.

five assumptions of the Hardy-Weinberg principle

1. Random mating

2. Infinitely large population size

3. No gene flow or migration

4. No mutation

5. Equal probabilities of survival and reproduction

Panmixis

Random mating within a breeding population

Random genetic drift

Changes in allele frequency that occur by chance alone

Gene flow

The movement of alleles from one population to another through mating among individuals from different populations (e.g., migration)

Linkage

Physical association of genes on the same chromosome

Linkage disequilibrium

non-random association of alleles at different loci

six reasons for linkage disequilibrium

1. Nonrandom mating

2. New mutation

3. Recent union of a population from two different populations with different allele frequencies

4. Low recombination rate

5. May be caused by random genetic drift

6. May be caused by natural selection

Quantitative trait

A measurable phenotype that depends on the cumulative actions of many genes and the environment

Polygenic

The genetic component of quantitative variation

Additive alleles

Combine to produce a heterozygote that is phenotypically the average of the two corresponding homozygotes

Heritability (h^2)

The proportion of the phenotypic variance that is genetic; expressed in a formula as h2 = VG/(VG + VE).

Fixation index (FST)

A measure of the variation in allele frequency among populations; can be expressed in the formulas as FST = [Vq /(q)(1-q)] or FST = 1/(4Nm + 1)

Isolation by distance

The further apart two or more populations are from one another geographically, the more genetically dissimilar they are

Ring species

Two populations which do not interbreed are living in the same region and connected by a geographic ring of populations that can interbreed

Genetic drift

Random fluctuations in allele frequencies

Heterozygosity

The frequency of heterozygotes in a population, defined by the formula H =2p(1-p), where p is the frequency of one of two alleles

Census size

When estimating population size, this is the number of individuals that you count, regardless of whether they’re reproducing or not.

Effective population size

The number of individuals in an ideal population (where all individuals reproduce) in which the rate of genetic drift would be the same as in the actual population.

Bottleneck

A severe, temporary reduction in population size

Founder effect

Genetic drift in a small colonizing population

Inbreeding depression

The resulting decline in fitness and fecundity that occurs when closely related individuals reproduce; increases homozygosity in individuals that are more likely to share the same recessive, deleterious alleles.

Neutral theory of molecular evolution

The great majority of mutations that are fixed are effectively neutral with respect to fitness and are fixed by genetic drift

Molecular clock

Evolutionary substitutions at the molecular level proceed at a constant rate, so the degree of sequence difference between species can serve as a way to estimate relative divergence times; can be calibrated to estimate actual times using data from the fossil record

Intelligent design

The theory that life, or the universe, cannot have arisen by chance and was designed and created by some intelligent entity

Natural selection

The process whereby organisms better adapted to their environment tend to survive and produce more offspring

Teleology

The explanation of phenomena by the purpose they serve rather than by postulated causes.

Adaptation

A characteristic that enhances the survival or reproduction of organisms that bear it relative to alternative character states

Fitness

Reproductive success as measured by the average per capita rate of increase; also defined as “Survival of the form (phenotypic or genotypic) that will leave the most copies of itself in successive generations”; consists of survival and reproduction

levels of selection

Genic selection, individual selection, and group selection

Aposematism

A warning signal to potential predators that prey are toxic or noxious

Batesian mimicry

The resemblance in appearance of a palatable or harmless species to an unpalatable or dangerous species that is usually avoided by predators

Müllerian mimicry

The resemblance of an unpalatable or dangerous species to another an unpalatable or dangerous species

Competitive exclusion principle

Two competing species that use exactly the same resources cannot coexist indefinitely; one will eventually be driven to extinction

Resource (or niche) partitioning

Species divide limited resources to reduce competition

Character displacement

The phenomenon where differences among similar species whose distributions overlap geographically are accentuated in regions where the species co-occur, but are minimized or lost where the species' distributions do not overlap

Group selection

A mechanism in which natural selection may favor an increase in fitness of a group of organisms, despite a reduction in individual fitness.

Altruism

The behavior of an animal that benefits another at the expense of its own fitness

Kin selection

Natural selection in favor of behavior by individuals that increases the chance of survival of their kin (who share a proportion of their genes)

Preadaptation

A character trait that originally evolved for a particular function that later served a new and different function

Exaptation

A more recent term for preadaptation as it does not have teleological implications

Naturalistic fallacy

What is natural, isn’t necessarily “good”; terms like moral or immoral, just or unjust, kind or cruel, cannot describe and do not apply to natural selection