LECTURE 3: Non-allelic Interactions Flashcards
Allelic Interaction vs Non-allelic interaction
AI: only one type of gene controls a single trait (1 phenotype)
NAI: two genes are controlling one trait (1 phenotype)
OTHER TERM for non-allelic interaction
gene interaction
NON-ALLELIC INTERACTIONS (6)
A. Epistasis
1. Dominant Epistasis
2. Recessive Epistasis
3. Duplicate Genes
4. Complementary Genes
B. Novel Phenotypes
NON-ALLELIC INTERACTIONS
NOVEL PHENOTYPES
- F2 phenotypic ratio
- definition
9:3:3:1
- DIHYRBID genotypes but 1 phenotypic trait is pinag-uusapan rather than 2.
example in chickens :
R_P_ - 9 walnut comb
R_pp - 3 rose
rrP_ - 3 pea
rrpp - 1 single
example in peppers:
Y_R_ - 9 red
Y_rr - 3 yellow
yyR_ - 3 brown (green + red)
yyrr - 1 green
NON-ALLELIC INTERACTIONS
RECESSIVE EPISTASIS
- F2 phenotypic ratio
- definition
9:3:4
- homozygous recessive gene masks the effects of other genes
example in color of mouses:
A_C_ - 9 agouti
A_cc - 3 albino (due to cc)
aaC_ - 3 black (due to aa)
aacc - 1 albino (due to cc)
wherein
A_ - agouti is dominant to black (aa)
C_ - color expression is dominant to color inhibition (cc)
cc - epistatic to A/aa (masks A_ or aa)
NON-ALLELIC INTERACTIONS
DOMINANT EPISTASIS
- 2 types
- F2 phenotypic ratio
- Complete dominance at both gene pairs BUT dominant gene masks the expression of other gene
12:3:1
example in color of squash:
W_Y_ - 9 white
W_yy - 3 white
wwY_ - 3 yellow
wwyy - 1 green
wherein:
W_ - white, epistatic to Y_ or yy
Y_ - yellow
yy - green
ww - no assigned, just “color”
- Consider genes: A and B
- A_ is dominant to a
- A_ is epistatic to B and b
- B_ is dominant to b
- bb is epistatic to aa
- bb and A_ has the same expression
13:3
example in feather color:
I_C_ - 9 white
I_cc - 3 white
iiC_ - 3 colored
iicc - 1 white
wherein:
I_ - color inhibition (also white) is dominant to color appearance (ii)
C _ - colored feather is dominant to white (cc)
NON-ALLELIC INTERACTIONS
COMPLEMENTARY GENE ACTION
- F2 phenotypic ratio
- definition
9:7
- either gene, when homozygous recessive, becomes epistatic to the other gene
example:
P_C_ - 9 purple
P_cc - 3 white
ppC_ - 3 white
ppcc - 1 white
wherein:
P_ - purple is dominant to white (pp)
C_ - color is dominant to non-color (also white) (cc)
NON-ALLELIC INTERACTIONS
DUPLICATE GENE ACTION
- F2 phenotypic ratio
- definition
15:1
- either gene, when dominant, is epistatic to the other gene
example:
A_B_ - 9 triangular
A_bb - 3 triangular
aaB_ - 3 triangular
aabb - 1 ovoid
wherein:
A_ - triangular is dominant to ovoid (aa)
B_ - triangular is dominant to ovoid (bb)
PSEUDOALLELES
- author, and year
- are they true alleles?
- definition
- described through the ______ in ___?
- Lewis (1951)
- no, but behave similarly
- two or more genes that are close together on a chromosome and have similar functions
- STAR-ASTEROID GENES in Drosophila
LEWIS EFFECT
- other term
- states that the phenotype is dependent on 2 things:
- position effect
1. not just the GENOTYPE but also…
2. position of genes on chromosomes
Does environment have an effect on phenotype?
yes
what AFFECTS development (2)?
GENES + ENVIRONMENTAL FACTORS
IMPORTANT TERMS in environmental influence on gene (4)
- penetrance
- expressivity
- pleiotropy
- phenocopy
PENETRANCE
- proportion of ___ that shows the ____
- 2 types?
- genotype - expected phenotype
- complete penetrance
- all will show the trait (100%) - incomplete penetrance
- not all will show the trait
EXPRESSIVITY
- degree in which?
- 2 kinds?
- a particular phenotypic effect is exhibited by an individual
- constant or narrow expressivity (everyone w/ same genetic mutation displays the exact same phenotypic expression)
- variable expressivity (everyone w/ same genetic mutation exhibit different degrees of a phenotype)
PENETRANCE vs EXPRESSIVITY
PENETRANCE (more on number of individs that express the phenotype)
- 100% expressed in all individs (complete)
- some will fully express, some will fully not (incomplete)
EXPRESSIVITY (more on severity of phenotypic expression)
- 100% same level (of severity) expressed in all individuals
- different levels of severity (may be 30%, 55%, or so on) per individual
PLEIOTROPY
- definition
- example
- one gene has MULTIPLE phenotypic effects
- sickle-cell anemia
PHENOCOPY
- main definition
- example
an ENVIRONMENTAL MIMIC of gene action
*environmental factor causes a specific phenotype emergence that resembles a genetically determined phenotype
THALIDOMIDE
- drug to cure morning sickness in pregnant women
- but CAUSED underdeveloped limbs (mimicked PHOCOMEILA which is due to genetic mutation)
other EXAMPLES of phenocopy (3)
- cosmetic surgery
- straightening/curling of hair
- use of insulin to control blood sugar
(mimicking genes’ effect on natural phenotype expressed)
ENVIRONMENTAL FACTORS responsible for differences in penetrance & expressivity
- external environment
- internal environment
P & E ENVIRONMENTAL FACTORS
external environment (4)
- temperature
- light
- nutrition
- maternal relations
P & E ENVIRONMENTAL FACTORS
internal environment (3)
- age
- sex (sex-limited traits/sex-influenced traits)
- substrates (metabolites within the body)
known study that helps determine the EFFECT OF GENES and ENVIRONMENT
+ what else is determined?
twin studies
difference - difference in the effects of genes and environment
2 types of twins
- identical - same genotypes
- fraternal - different genotypes
2 possibilities in the TWIN STUDIES and their CONCLUSIONS if ever
- when phenotypic similarities are greater in IDENTICAL than fraternal:
then there is GREATER GENETIC INFLUENCE than environmental factors
- when phenotypes are the SAME for identical and fraternal:
then there is GREATER ENVIRONMENTAL INFLUENCE than genetic factors
2 TERMS important in the TWIN STUDIES
+ 2 possibilities
and what was proven?
- Concordant - both twins show/don’t show the trait
- Discordant - only one of the twins show the trait
- High heredity influence
- high concordance in identical
- low concordance in fraternal - Low heredity influence & high environmental influence
- equal concordance and discordance between identical and fraternal twins
1 was proven
