exam 1: relating phenotype to genotype Flashcards
types of inheritance that have traits controlled by 1 gene (locus) but dont show the typical ratios
- incomplete dominance: one gene mask the other
- codominance: work tgt, see them equally
- > 2 alleles
4.pleiotropy:one gene control multiple traits
- lethality: bad genetics that are lethal
type of inheritance that dont show medelian ratios because they are controlled by many loci
multifactorial
-epistasis
-heterogeneous traits
incomplete dominance
1 allele DOES NOT completely mask the presence of another
-occurs when 1 allele is functional (expressed), 1 allele is functional but not enough to mask the other
-phenotype is a heterozygous between the two homozygous phenotypes (red is not enough to completely mask the nonfunctional allele
homozygous: red and white
heterozygous: pink
1:2:1
-> true breeding of white is nonfunctional
codominance
both alleles at a locus are expressed equally in the phenotype
(both alleles are functional & equally in the phenotype)
-blood types
more than 2 alleles
how to multipple alleles arise? mutation (1 in 3 gametes)
*mutant allele: <1% frequency (distinctly rare)
*wild allele:>1% frequency (common)
dominance series:>2 alleles at a locus that varibale dominance relative to each other
ex. coat color in mice
Agouti: wt=A
Black back:mutant=at
black:mutant=a
order of dominance: A>at>a
pleiotropy
1 locus affects many traits(1locus affects > 1 phenotypic trait
ex. phenylketonuria
prevents humans from breaking down phenylalanine so it accumulatesf in the brain
=> mental retardation, musty order to skin, blond hair, and light skin
lethality
how is it different from fetal?
genetic combinations are bad so embryo stop develop
-embryo never born
*when doing punett square, ross out the genotype that will die (2/3: 66% surviving)
multifactorial traits
multiple genes affecting 1 trait
*true breeding lines (coming from diff ancestors)
yields a 9:7 ratio (variation of 9:3:3:1 resulting from complementary gene action)
complementary gene action
when crossed, one parent provides what the other is missing and vice versa, genotypes complement each other
what can a complementation test tell u?
cross 2 true breeding parents (with same phenotype) from a separate line
-> if all f1’s have phenotype different than parents, you can assume more than 1 gene affect trait and parent carry mutations at diff genes.
epistasis
one genetype at 1 locus completely mask the other genotype at a diff locus
**recessive (homozugous recessive) vs. dominant (homozygous/heterozugous-only need one dominant allele)
epistasis: recessive vs dominant
homozygous recessive:
when homozygous recessive genotype at 1st locus masks the presence of an allele at 2nd locus
-ex: coat color in retrievers (e is epistasis to b)
if have two ee then the god will be brown no matter what alleles are at the B locus (__ee)
dominant:
when the presence of 1 dominant allele at 1 locus masks the presence of allele at the 2nd locus
ex: summer squash
fruit color controlled by 2 loci: A & B
if a dominant B allele, fruit will be white no matter what alleles present at A locus
- A_bb=yellow
-aabb=green
-_ B=white
heterogenous traits
traits controlled by many loci where mutation in any one of the loci can give rise to the same phenotype
ex:deafness in humans
-50 loci in humans control hearing
-mutation (recessive) in any of them can produce same phenptype of deafness
-possible for 2 deaf ppl w mutations at differnt loci to have that are not deaf
->offspring would be heterozygous at loci that are homozugous recessive in parents
=>gene action:complementary gene action
not all individuals with same genotype have the same phenotype…why?
- penetrance
2.expressivity
3.modifier genes - environmental differences
5.chance!
penetrance
% of individuals in a pop that have a specific genotype and express the corresponding phenotype
ex. retinoblastoma in humans
-dominant mutation in 1 locus
-only 75% of ppl w mutant allele develoop disease so penetrance=75%
(hace dominant allele, only 75% have the phentotype)
expressivity
degree with which specific genotype is expressed as a specific phenotype (how intense?)
ex. retinoblastoma in humans
some ppl w mutant allele have disease in 1 eye
, some have it in both eyes
modifier genes
alter phenotypes produced by alleles at other loci
-how does this differ from epistasis? mask completely
ex.tail length in mice
-length controlled by single locus
-diff true breeding lines of mice with same genotype for tail length locus have different tail lengths
-linen specific differences due to modifer gene action
environment:
any external force (including in utero)
-may affect penetrancen (whether it is expressed/not) and/or expressivity (how intense)
ex: temp and color in Siamese cats
-color produced by enzyme that only function at lower temp
-hve color on extremities because those body parts are colder
chance
no 2 calicos have the same phenotype even though color genotype
do continuous variations follow mendel laws ? what cause this phenotypic variation?
yes, they do
-continuous varible traits (height,weight, skin color)
*additive gene action
additive gene action
presence of specific alleles at loci controlling specific trait increase expression of that trait
ex: height
-height controlled by 1 locus with 2 alleles
-A0 add nothing
-A1 add 2 unit
A0A0=0 unit tall
A0A1=1 unit tall
A1A1=2 units tall
