genetics exam 4

gene interaction

genes/alleles work together to influence phenotype

penetrant individual

phenotype is consistent with genotype

non-penetrant individual

phenotype that is not generally associated w/ genotype

incomplete penetrance

not all individuals w/ a genotype have same phenotype

variable expressivity

same genotype can have varying degrees of trait or symptoms

position effects

physical location of a gene may influence expression

environmental effects

environment can affect observed phenotype

temperature-sensitive allele enzyme

functional at lower temps (extremities of animal) , non-functional at higher temps

pleitropy

single gene influences multiple traits

effects of pleiotropy

if it fails in making a particular protein, many suffer (widespread effects)

single-gene trait

inheritance where single gene codes for a trait (wild type, mutant) It is MENDELIAN

biosynthetic pathways

interacting genes that produce molecular compound

signal transduction pathways

receive chemical signals from outside cell and tell inside of cell

developmental pathways

direct growth, development, & differentiation of body parts/structures

how biosynthetic pathway works

one step provides substrate for next step until end product; every step has to do their job or it won’t work (adenine)

how signal transduction pathway works

occurs via transmembrane proteins; activate TFs that control expression of genes encoding other TFs → genetic cascade

genetic dissection

approach to investigate steps of biosynthetic pathways

what genetic dissection determines

number & order of steps, the step affected by mutation

how does genetic dissection determine where mutation is

the intermediate compound made in the step before mutated will accumulate

genetic heterogeneity

mutations in different genes produce same/similar phenotypes

genetic complementation

two mutant alleles from parents complement each other to restore the wild type (MUTATIONS of parents affect DIFF GENES)

complementation testing

two pure-breeding organisms with similar mutant phenotypes are mated

in complementation occurs in complementation testing

wild type offspring = mutations in parents are in 2 DIFF GENES

if complementation DOES NOT occur in complementation testing

all mutant offspring = mutants in parents are in SAME GENE

complementation analysis

multiple crosses performed for many pure-breeding mutants to determine how many diff genes contribute to phenotype

complementation group

mutations mutually fail to complement one another (SAME Mutated gene) (number of groups = number of genes affecting trait)

epistasis

gene interactions where one gene modify/prevent expression of another gene

epistatic gene (modifier gene)

the gene that modifies/prevents the other gene

hypostatic gene

the gene that is modified/prevented by other gene

epistatic interactions detected

phenotypic ratios modified resulting in genotype classes being combined

complementary gene interaction

when genes work in tandem to produce a single gene product (work together to produce flower color) (9:7)

duplicate gene action

genes encode same product/products that have same effect in pathway (15:1)

recessive epistasis

homozygous recessive at one locus will mask phenotypic expression of alleles at second locus (9:3:4)

dominant epistasis

dom allele at one locus will mask phenotypic expression of alleles at second locus (12:3:1)

dominant suppression

dom allele at one locus completely suppresses phenotypic expression of alleles at second locus (13:3)

coupling

mechanism that kept two parental gamete combinations together (not segregating independently)

syntenic genes

genes located on same chromosome

linked genes

genes on same chromosome that are close enough together that alleles DON’T assort INDEPENDENTLY

what happens w/ linked genes

they’re so close they get inherited together

how would linked genes not get inherited together

crossing over or recombination (moves one to another chromosome)

recombinant chromosomes

alleles/syntenic genes shuffled when crossed over between homologous chromosomes

parental chromosomes (non-recombinant chromosomes)

homologs that do not shuffle alleles

crossing over less likely

b/w genes near one another

crossing over more likely

genes farther apart on chromosome

linked genes are always

syntenic and near each other

parental allele combinations are observed higher frequency than predicted when

genes are linked

how to recognize gene linkage

comparing observed frequencies w/ expected under independent assortment

complete genetic linkage

when no crossing over occurs between genes

complete genetic linkage produces

only PARENTAL gametes formed

incomplete genetic linkage

mixture if parental & recombinant gametes produced

incomplete genetic linkage ratios

two parental types = in frequency; 2 recombinant types = in frequency

recombinant frequency r formula

# of recombinant progeny / total # of progeny. x 100%

crossing over in males

between X and small area of Y; lower rate or none at all

recombination frequency

reflection of physical distance b/w 2 genes on chromosome

genetic mapping

mapping of relative locations of genes on a chromosome

two-point test-cross analysis

determine distance and linkage b/w 2 genes on a chromosome

“ponit” refers to

genetic locus

“two-point” refers to

two linked genetic loci

recombinant frequency r b/w 2 genes converted into units

map unit (m.u.) = centiMorgan (cM)

tree-point test cross

3 linked genes; hetero x homo recessive

incomplete linkage w/ 3-point

produces 8 diff gamete genotypes w/unequal frequencies

no crossing over in 3-point test cross produces

parental gametes

least frequent crossovers

double crossovers

single crossovers involve

one chromatid from each homolog (doesn’t matter which crosses over; same result)

where does crossing over occur

at the four-strand stage (tetrad) after replication

two-strand double crossovers

produce ONLY parental gametes; NO crossing over

three-strand double crossovers

produce 50% parental & 50% recombinant gametes

four-strand double crossovers

produce ALL recombinant gametes

pattern expected when syntenic genes are far enough apart to produce recombination frequencies of 50%

Mendel’s Law of Independent Assortment

recombination frequency is low where

near centromere

discontinuous variation

phenotypes of single-gene traits w/distinct separate categories ;no in-between

continuous variation

polygenic traits w/wide range of possibitilies

additive genes

in polygenic traits: genes whose effects on a trait add together with contributions from each genes

major genes

genes that strongly influence a trait (having to do w/additive effects)

modifier genes

genes that influence to a lesser degree having to do w/ additive effects)

as number of additive genes contributing to a trait increase,

the number of possible phenotypic categories also increase, and less obvious the demarcation between categories

quantitative traits

traits controlled by many genes because “phenotypes” are quantitative values (ex. tibia length=2.57 cm)

quantitative trai loci (QTL)

genes (or genome regions) that contribute to phenotypic variation of quantitative traits

genetic variation results in

• diff alleles/versions of proteins

• variation in amount, timing, or location of protein production (gene expression)

environmental variation

influences protein function or gene expression

genotype-by-environment interaction occurs when

genetic diffs cause diff sensitivity/response to environmental factors

values of quantitative traits determined by

combination of genetic and environmental influences

when no effect of environment occurs

genotype corresponds to distinct phenotype

the greater the effect of environment

the wider the potential range of phenotypic values that may occur for given genotype (=phenotypic plasticity)

variance (s2)

measure of spread of distribution around mean

phenotypic plasticity

when organisms w/ same genotype develop diff phenotypes in diff environments

reaction norm

pattern of genotype’s change in phenotype across range of environments

genotype-by-environment interaction

genetic variation for phenotypic plasticity

polyphenism

reaction norm w/ discrete morphs rather than continuous variation

reciprocal transplant

creating a common garden at multiple location along environmental gradient to observe if differences at maturity is due to environmental or genetic factors

broad sense heritability (H2)

estimates proportion of phenotypic variation that’s due to total genetic variation

narrow sense heritability (h2)

estimates proportion of phenotypic variation that’s due to additive genetic variation

selection differential (S)

diff b/w mean of selected individuals & overall pop mean

response to selection (R)

how much trait value is predicted to change in pop under selection

if trait has h2=0

then it’s NOT heritable & canNOT respond to selection

molecular genetics

how genetic info is encoded, replicated, & expressed

transmission genetics

principles of heredity & how traits passed across gens

population genetics

genetics variation of pops across space & time (change = evolution)

gradual evolution results from

small genetic changes (mutations) acted on by natural selection

evolution

change in allele frequencies across gens (groups within species)