life science unit 14 - unit 20

dominant

always expressed, produces a characteristic which will be shown in organism that possesses it, produces a polypeptide whose effect will be exerted/shown in organism that possesses it

recessive

expressed only in the absence of a dominant, produces a characteristic that can be overridden by a dominant, produces a polypeptide whose effect can be overridden by a dominant

homozygous

possessing identical alleles in a given gene pair

heterozygous

possessing two different types of alleles in a given gene pair

phenotype

characteristics encoded for by genes

genotype

allelic content of a gene pair

simple dominance

inheritance pattern in which there is a dominant allele in a gene pair that can completely override the recessive allele

incomplete dominance

inheritance pattern in which neither allele in a gene pair can completely override the expression of the other allele (all dominant)

dihybrid cross (possible extra credit question)

cross which considers two gene pairs per parent

monohybrid cross

cross which considers only one gene pair per parent

polyhybrid cross

cross which considers many gene pairs per parent

law of independent assortment*

alleles from different gene pairs will unit in gametes in all combinations possible

law of allelic segregation

alleles of the same gene pair will separate from one another during gamete formation

gene (structural + functional)

sequence of DNA nucleotides that encode for a specific polypeptide/mRNA sequence

the biological purpose of meiosis

to produce gametes (sperm + egg cells) for the purpose of sexual reproduction

meiosis

process of making smaller

46 monads (46 DNAs), 46 dyads (92 DNAs), 23 dyads + 23 dyads (46 DNAs, 46 DNAs), 23 monad + 23 monad + 23 monad + 23 monad (4 × 23 DNAs); 1 diploid cell —> 4 haploid cells

the biological purpose of sexual reproduction

to create genetic diversity in offspring

three sources of genetic variation from sexual reproduction

crossing over, random alignment, recombination

prophase I

nuclear envelope disintegrates, DNA molecules compacted into dyad chromosomes, homologous chromosomes pair up into tetrads, crossing over occurs

metaphase I

random alignment of tetrads, no prometaphase

anaphase I

centromeres not broken apart, tetrads separate

telophase I

cytokinesis, two cells each have one member of each tetrad

prophase II

nuclear envelope reforms, no more crossing over

metaphase II

two dyads have a random arrangement + line up

anaphase II

dyads separate into monads, centromeres broken

telophase II

cytokinesis, haploid monad daughter cells form

syngamy

fusion of gametes to create a zygote

when do bivalents (tetrads) form?

prophase I

what major event occurs during bivalent (tetrad) formation? what is the biological significance of this event?

crossing over, to create greater genetic diversity in the offspring

how many tetrads do humans have?

23

random alignment + when does it occur + biological significance

creates different combinations of paternal + maternal chromosomes in gametes; occurs at metaphase I, to create greater genetic diversity in offspring

when do bivalents (tetrads) split?

anaphase I

when do chromatids split?

anaphase II

when are gametes formed?

at the very end of meiosis

diploid

cell that has only two members of each homologous pair

haploid

cell that has only one member of each homologous pair

carrier

person who possesses an allele, but does not have the phenotype associated with it; typically a person with a heterozygous genotype

pleiotropic

one gene pair/allele having multiple phenotypic effects

autosome

no-sex chromosomes; those other than X + Y

lethal

deadly

major inheritance patterns + physical characteristics associated with albinism

-inability to synthesize an enzyme that manufactures melanin

-extremely pale skin, white hair, pink/blue eyes, tendency to be near-sighted/have strabismus

-recessive

major inheritance patterns + physical characteristics associated with tay-sachs disease

-children likely to become blind, deaf

-missing an allele that produces the enzyme to digest nerve cell gangliosides

-homozygous recessive/2 recessive genes

major inheritance patterns + physical characteristics associated with cystic fibrosis

-recessive allele + CFTR gene

-#1 genetic illness in the U.S.

-buildup of mucus that clogs vital organs

-average lifespan around 35 years old

major inheritance patterns + physical characteristics associated with huntington’s disease

-lethal condition that can be passed onto offspring

-dominant

-presents itself in adulthood/late adulthood

major inheritance patterns + physical characteristics associated with fragile X (sex-linked condition)

-pleiotropic allele produces abnormal cartilage growth in the face caused by the fragile site on X chromosome

-leading genetic cause for mental retardation

-recessive

-only found on X chromosome

major inheritance patterns + physical characteristics associated with colorblindness (sex-linked condition)

-recessive

-found on X chromosome

major inheritance patterns + physical characteristics associated with hemophilia (sex-linked condition)

inherited genetic, X-linked recessive inheritance disorder that impairs ability to make blood clots

polygenic

conditions dependent upon alleles in 2+ gene pairs

multi-allelic

single gene pair in which there are > two possible alleles

mechanism of SRY translocation

during gamete production, SRY gene is transferred from the Y to the X chromosome during crossing over

result of SRY translocation

individual is XX, but has traits — muscular, skeletal, physiological, etc. due to masculinizing SRY gene, including internalized “testes” that produce testosterone in high volumes

ecology

scientific study of how organisms interact with each other + with their nonliving environment

ecological niche

manner in which an organism uses the resources in and is influenced by the conditions of its habitat; determined by an organism’s physical adaptations

habitat

physical place/type of place where an organism lives

physical adaptation (feature not process)

phenotypes that enable a given organism to survive + reproduce using a given niche

niche partitioning (may be permanent/temporary)

division of niches between species so as to cut down on competition

resource

material that is used + potentially used up — food, water, nesting materials, open space, shelter, etc.

environmental conditions

background features of the habitat — temperature, humidity, salinity, altitude, irradiance, pH, etc.

realized niches

actual set of resources utilized, resorted to when competition with other species sets in + must now be avoided

fundamental niches

largest array of resources an organism can utilize

competition + its consequences

antagonistic struggle for a common resource; produces losses including time, energy, other opportunities, tissue, life

competitive exclusion principle (Gause’s principle) + its consequences

no two species can use the same niche in the same habitat; one/the other/both will inevitably be outcompeted

direct (physical) competition

physical confrontation with another organism

indirect (exploitive) competition

quicker/more efficient use of a resource

interspecific competition

between different species

intraspecific competition

within a species, far more common, far less avoidable

which competition is most common?

intraspecific competition

populations

individuals within a species interact with each other as members of a population/colony; a group of organisms that interbreed so as to produce viable offspring

biotic potential

density-dependent factors

predators, disease, food + water shortages, buildup of wastes, lack of space/nesting sites, etc.

density-independent factors

drought, hot spells, cold snaps, fires, floods

carrying capacity (COMPONENT OF THE ENVIRONMENT, NOT POPULATION)

environment’s ability to hold/carry a specific # of individuals for a prolonged period of time

S-shaped curves

logistic, in close relationship to available resources

which curve is associated with exponential growth?

J-shaped curve

J-shaped curves

exponential, at a fixed rate per time period

which curve is associated with logistic growth?

S-shaped curve

logistic growth

exponential growth

what inevitably happens to populations that undergo prolonged J-shaped growth?

population overshoots carrying capacity, crashes + falls back downward, then population may be eliminated altogether/have some survivors to repeat the process

five conditions needed to achieve Hardy-Weinberg equilibrium

gene frequencies within populations will remain stable but there must be:

-no random events that differentially eliminate alleles

-no migration in/out of the population

-no reproductive/survival advantage to any gene/genotype

-all mating must occur at random (no selection criteria for mates)

-mutations may not occur

mutation

an alteration to the nucleotide sequence of a gene (violation of rule 5)

factors causing mutations

exposure to radiation, exposure to toxins, random replication errors in DNA synthesis

gene pool

all inheritable alleles found within a given population

allele (gene) frequency

numeric rate at which a gene/allele occurs in a gene pool, relative to the other alleles in its gene pair

genetic diversity

variety of genes + genotypes in a gene pool

genetic drift

changes in gene (allele) frequency owing to random factors (violation of rule 1)

gene flow

movement of genes (alleles) into/out of population resulting from migration (violation of rule 2)

environmental selection

conditions of habitat create differential survival + replication of specific alleles (violation of rule 3)

sexual selection

mate pairing criteria create differential survival + replication of specific alleles (violation of rule 4)

evolution

changes in gene frequencies in populations over time

evolutionary fitness

ability of an organism/allele to survive + reproduce relative to other individuals/alleles within the population

which pattern of natural selection is likely to lead to speciation?

only disruptive selection

directional selection

genetically-related change in mean over time follows a progressive trend; selective pressure moves population from one average to another

stabilizing selection

no genetically-related change in population mean over time; selective pressure keeps population centered around an average

disruptive selection

genetically-related change in mean over time produces two “means” (modes); selective pressure splits population around two averages/modes

species

population of organisms which is reproductively isolated from other populations of organisms

speciation

evolution of reproductive isolation in two populations which previously interbred

allopatric speciation

speciation occurs in two separate areas; usually involves some geographic barrier — river, canyon, open ocean, mountain range

parapatric speciation

speciation occurs in two adjacent areas (next to each other); anthoxanthum grass

sympatric speciation

speciation occurs in the same area; usually involves some sudden mutation