BIS 2B Midterm 2

Mendel

Augustinian monk and botanist whose experiments in breeding garden peas led to his eventual recognition as founder of the science of genetics (1822-1884)

blending model

Blending model:
Offspring are a blend of both parents (i.e. in modern terms, alleles would blend together to form a completely new allele)
The characteristics of the blended offspring are passed on to the next generation
Variation is washed out over time

particulate model

Offspring are a combination of both parents
The characteristics of both parents are passed on to the next generation as separate entities
Variation is maintained over time

law of independent assortment

Alleles of different genes assort
independently during gamete
formation.

law of segregation

The two copies of a gene separate when an individual makes gametes.

1. Before Meisosis 1, each homologous chromosome replicates

2. At the end, the copies are seperated into two seperate daughter cells

3. at the end of Meisos II, there are 4 hapoid daughter cells with one chromosome each (one allele for each gene)

law of dominance

dominant allele masks recessive one

character

as a heritable feature for which variants exist ie flower color

trait

as a particular variant for the character that exists ie purple and white flowers

diploid

2 sets of chromosomes

haploid

An organism or cell having only one complete set of chromosomes.

wild-type

allele, genotype, phenotype that is the most common form of expression

dominant

Describes a trait that covers over, or dominates, another form of that trait.

recessive

An allele that is masked when a dominant allele is present

allele

different forms of a gene for each variation of a trait of an organism.

gene

A segment of DNA on a chromosome that codes for a specific trait

locus\`

the specific location or position of a gene, DNA sequence, on a chromosome.

heterozygous

An organism that has two different alleles for a trait

homozygous

An organism that has two identical alleles for a trait

hemizygous

A chromosome in a diploid organism when only one copy is present, ie males and the X chromosome from their mothers

controlled cross

true breeding dominant+ recessive--\> F1 generation (heterozygotes)
Cross-fertilization of two true-breeding plants with different trait
-heterozygous F1 self pollinate--\> F2 generation, 3:1 ratio of dominant:recessive

monohybrid cross

A cross between two individuals, concentrating on only one definable trait

dihybrid cross

A cross between individuals that have different alleles for the same gene

test cross

used to find if dominant phenotype hetero or homozygous: cross with recessive individual and analyze results

probability

look at probability of alleles and multiply by each other

multiple allele trait

Multiple allele trait is a trait that has more than two alleles or gene options. Blood type is an example: the genes are A, B, and O. Any one person can only carry two of these genes since we are diploid.

incomplete dominance

A pattern of inheritance in which two alleles, inherited from the parents, are neither dominant nor recessive. The resulting offspring have a phenotype that is a blending of the parental traits.

codominance

A condition in which neither of two alleles of a gene is dominant or recessive, both are fully expressed ie blood type

pleiotropy

A single gene having multiple effects on an individuals phenotype ie Siamese cats

epistasis

Phenotypic expression of one
gene is influenced by another gene.

heterosis

("hybrid vigor"): A cross between two different truebreeding
homozygotes can result in offspring with stronger,
larger phenotypes.

phenotypic plasticity

the ability of an organism to change its phenotype in response to changes in the environment.

penetrance

The percentage of individuals with a particular genotype that actually displays the phenotype associated with the genotype ie Huntington disease

expressivity

Degree to which genotype is
expressed in an individual.
Example: Rabbits in regions with different
temperatures may show different coat color patterns.

discrete variation (qualitative)

in genetics, inherited traits that have a limited number of variations, such as the ability or inability to roll one's tongue

continuous variation (quantitative)

Variation measured on a continuum rather than in discrete units or categories (eg height in human beings).

quantitative trait locus

One of a set of genes that together determine a complex
character that exhibits quantitative variation.

polygenic inheritance

combined effect of two or more genes on a single character, One phenotype is controlled by two or more genes, also described as: continuous, additive,
dosage-dependent, quantitative.
By increasing the number of genes controlling a trait, the number of phenotype combinations also increase, until the number of phenotypes to which an individual can be assigned are no longer discrete, but continuous, bell curve distribution

linked genes

Some genes were inherited together; the two loci
were on the same chromosome

linkage group

All of the loci on a chromosome

linkage mapping

-The physical distance between two loci dictates the frequencey of crossover between the loci, the smaller the distance, the less chance of crossover, use test cross to expose genotype

absolute linkage

genes at different loci
on the same chromosome do sometimes
separate.

crossing over

Genes may recombine during prophase I of
meiosis

recombinant

Chromosomes exchange corresponding segments.
The exchange involves two chromatids in the
tetrad;

recombinant genotype

A genotype that the offspring has that is not the same as one of the genotypes that one of the parents have.

recombinant frequency

the proportion of offspring of a genetic cross that have phenotypes different from the parental phenotypes due to crossing over between linked genes during gamete formation
DIVIDE NUMBER OF RECOMBINAT/TOTAL OFFSPRING

FREQUENCIES HIGHER WHEN LOCI ARE FURTHER

map unit

distance b/w genes,recombinant frequency of .01\=centimorgan\=cM

genetic maps

arrangement of genes along a
chromosome

sex linked

Gene located on a sex chromosome

autosome

Any chromosome that is not a sex chromosome

sex chromosome

X and Y chromosomes.

hemizygous

A gene present on the X chromosome that is expressed in males in both the recessive and dominant condition

color blindness

A sex-linked recessive disorder carried on the x chromosome in which an individual cannot perceive certain colors.

gene pool

is the set of all genes, or genetic information, in any population, usually of a particular species.

population

summation of all the organisms of the same group or species, which live in a particular geographical area, and have the capability of interbreeding.

genotype frequency

frequency of genotypes in population

allele frequency

proportion of alleles in population

evolutionary change

change in the heritable traits of biological populations over successive generations.

hardy weinberg principle

Allelic and genotypic frequencies in large populations reach an equilibrium after one generation of random mating, and remain unchanged thereafter, assuming:

1. no mutations

2. no interpopulation gene flow

3. large population size (no genetic drift)

4. random mating

5. no selection

hardy weinberg equilibrium

equilibrium reached when the HW principle has been achieved

random mating

no selective mating in which animals chose mate depending on phenotype

nonrandom mating

Mating among individuals on the basis of their phenotypic similarities or differences, rather than mating on a random basis

inbreeding

continued breeding of individuals with similar characteristics to maintain the derived characteristics of a kind of organism

mutation

any change in the nucleotide sequence of DNA
• adds new alleles to a population
• ultimate source of genetic variation in
populations

gene flow

movement of genes between
populations resulting from the migration/dispersal
of individuals or the movement of gametes (e.g. in
pollen) between populations
• can add new alleles to the gene pool or change
allele frequencies

genetic drift

process by which allele frequencies within a
population change by chance alone as a
result of (gamete) sampling error from
generation to generation
Harmful alleles may increase in frequency, and
rare advantageous alleles may be lost.

adaptive evolution

evolution that results in a better match between organisms and their environment

discrete traits

controlled by allelic variation at one or two loci

quantitative traits

traits determined by allelic variation at many gene loci

stabilizing selection

• occurs when the two extremes of a trait are selected
against
Example:
• plant that is too short
may not be able to
compete for light with
other plants but
• plant that is too tall
may suffer wind damage
in windy environments

directional selection

• occurs when one extreme of the phenotypic distribution of
a trait is selected against

disruptive selection

occurs when selection acts against individuals in the middle
of the trait distribution
• result is a bimodal, or two-peaked, curve

sexual selection

form of nonrandom
mating that favors traits that increase the
chances of reproduction.

antagonistic interactions

predation, herbivory, parasitism, all benefit one species and not the other

mutualism

both species benefit

competition

neither benefits

commensalism

one benefits, the other neutral

ammensalism

one does not benefit, the other neutral

coevolution

• evolution of an adaptation in one species can lead to
evolution of a reciprocal adaptation in species with
which it interacts, a process called "reciprocal
adaptation"

coevolutionary arms race

a series of reciprocal
adaptations

oligophagous

specialists on one or few,
often taxonomically related, taxa

polyphagous

feed on many unrelated
plant species

microparasite

maller than hosts; live and reproduce inside host, many pathogens

ectoparasite

live outside host

interspecific

interactions among individuals of two or more
species that share a limited resource

intraspecific

competition for resources within species

competitive exclusion

occurs when one of the species
prevents all individuals of a second species from
using a resource and the inferior competitor goes
locally extinct

resource partitioning

competing species evolve ways to divide up or "partition" the
common limiting resource so all species coexist

interference competition

a competitor interferes
with another competitor's access to a resource

exploitation competition

limiting resource is
available to all competitors but one competitor is
more efficient in using a resource than another

character displacement

• refers to an evolutionary phenomenon in which
species that compete for the same resource within
the same area tend to diverge in morphology and/or
behavior

niche

set of physical and biological
conditions it needs to survive, grow, and reproduce
partly defined by the resources available in the
environment

fundamental niche

defined by a species'
physiological capabilities

realized niche

defined by a species' interactions
with other species.

diffuse coevolution

whole groups of species interact with other groups of species, leading to changes that cannot really be identified as examples of specific, pairwise coevolution between two species

pollination

a process in which pollen is transferred to the female reproductive organs of seed plants, thereby enabling fertilization and reproduction through growth of the pollen tube and eventual release of sperm.

frugivore

herbivore or omnivore that prefers fruit

batesian mimicry

a harmless species has evolved to imitate the warning signals of a harmful species directed at a predator of them both

mullerian mimicry

a natural phenomenon in which two or more distasteful species, that may or may not be closely related and share one or more common predators, have come to mimic each other's warning signals1

competitive exclusion principle

Ecological rule that states that no two species can occupy the same exact niche in the same habitat at the same time

phenetic species concept

Linnaus,based on
overall similarity in phenotype, not concerned
with the processes that lead to the origin of
species nor with those that cause them to
remain distinct once they have diverged.