gene interactions marie Černá lecture no 406-h. mendelian genetics: 1 character = 1 gene genes are...
TRANSCRIPT
Gene Interactions
Marie Černá
Lecture No 406-H
Mendelian genetics: 1 character = 1 geneGenes are segregating independently
on each other
Gene interactions:1 character = two or more genes Interaction of two genes
– genotype ratio as in dihybridism – less phenotype classes
Gene Interactions
• Reciprocal interactions• Epistasis - dominant and recessive• Inhibition• Complementarity• Multiplicity
Reciprocal interactions
= Interactions without change of phenotype ratioF2: 9 : 3 : 3 : 1, B1: 1 : 1 : 1 : 1
The identical character can occur in more various independent forms, which of them is determined by one gene.
gene 1 = A1 Phenotype A2 = gene 2
Reciprocal interactions
Product color of paprika:Gene 1: allele R – anthocyan = red coloring Gene 2: allele Cl – chlorophyll degradation =
yellow pigmentPhenotype 1: R-Cl-– red (anthocyan)Phenotype 2: R-clcl – brown (red + green)Phenotype 3: rrCl- – yellowPhenotype 4: rrclcl – green (chlorophyll)
P
1)x
2)x
F1
RRClCl rrclcl RRclcl rrClCl
RrClcl
R-Cl- R-clcl rrCl- rrclcl 9 : 3 : 3 : 1
F2
Epistasis
One of alleles of the epistatic gene suppresses phenotype manifestation of the hypostatic gene.
It is then an unilateral relation - among alleles of two various genes (M > N)- among alleles of more various genes (M > N > R > S)
Dominant Epistasis
- Dominant allele of one gene has epistatic effect.Dominant alleles of both genes allow the same
precursor processing in the same direction, but into different final products.
Epistatic effect will have dominant allele of that of both genes, which can lead by biosynthetic processes to more expressive form of a trait, and by this way will cover an effect of dominant allele of the hypostatic gene.
Dominant Epistasis
Flower color of dahlia: depends on hydroxylation degree of colorless precursor of flavon pigment
Gene 1: allele Y – higher degree = dark yellowGene 2: allele I – lower degree = light yellow
(ivory white)
Phenotype 1: Y-I-, Y-ii – dark yellowPhenotype 2: yyI- – light yellowPhenotype 3: yyii – white
P
1)x
2)x
F1
YYII yyii YYii yyII
YyIi
Y-I- Y-ii yyI- yyii 9 : 3 : 3 : 1
12 : 3 : 1
F2
Examples of dominant epistasis in human
Determination of eye coloring
- depends on type and density of pigment in eye iris
brown coloring (melanin) gene EYCL3 = BEY2 on chr.15
? light-brown, nut coloring gene EYCL2 = BEY1 on chr.15
genes dominant epistatic towards „lipochrome“ gene
green coloring (lipochrome) gene EYCL1 = GEY on chr.19
? 2nd gene
gene dominant hypostatic towards „melanin“ gene
Determination of eye coloring
BEY > GEY
B-G-, B-gg _brown → intensity depends on
quantity of pigment
bbG- _green
bbgg _blue (albinotic) →
inability of pigment formation
Which parents can have which children?
Examples of dominant epistasis in human
Determination of hair coloring
- depends on type and density of pigment in hair fiber
eumelanin = dark dye - black/brown hair
gene HCL3 on chr.15 - association with eye brown coloring
gene BRHC on chr.19 - association with eye green coloring
gene dominant epistatic towards other two genes
pheomelanin = red-and-yellow dye - rusty-red hair
gene RHC on chr.4
gene dominant epistatic towards „blond“ gene
? gene x → low density - blond hair
Determination of hair coloring
HCL3 (BRHC) > RHC > x
H-rr _black (↑ pigment) / brown (↓ pigment)
H-R- _dark-brown
hhR- _rusty-red
hhrrX- _blond
hhrrxx _white (albinotic) →
inability of pigment formation
_grey → degraded products of pigment
Which parents can have which children?
Recessive Epistasis
- Recessive allele of one genein homozygous state has epistatic effect.
Dominant alleles of both interactive genes participate in multistage synthesis of the same final product.
Still dominant allele of the epistatic gene functions in one of initial phases of biosynthesis, while dominant allele of the hypostatic gene functions not until in one of its later phases.
Recessive Epistasis
Flower color of sage: depends on hydroxylation degree of colorless precursor of flavon pigment
Gene 1: allele P – lower degree = rose coloringGene 2: allele A – higher degree = violet coloring
Phenotype 1: P-A- – violetPhenotype 2: P-aa – rosePhenotype 3: ppA-, ppaa – white
P
1)x
2)x
F1
PPAA ppaa PPaa ppAA
PpAa
P-A- P-aa ppA- ppaa 9 : 3 : 3 : 1 9 : 3 : 4
F2
Examples of recessive epistasis in human
AB0 system of blood groups metabolite antigens
Precursor H, A H H, B
H
- (unchanged precursor)
H or h alleles are recessively epistatic
against A or B alleles hh genotype codes the blood group 0
even in the presence of A or B alleles hh = Bombay allele
transferase H transferase A
transferase B
0hh
Recessive epistasis is manifested in the case of the gene for secretion of antigens A, B, H:
Genotypes SS, Ss secret antigens into saliva and body fluids
Genotype ss does not secret any antigens, even though they are present in erythrocytes
Epistasis- unilateral relation
• Dominantsubstrate
Y-------> P1 I-------> P2
• Recessivesubstrate
B A-------> P0 -------> P
InhibitionIt is certain analogy of dominant epistasis.
But, in comparison with it, inhibitive allele I has not another effect on phenotype than ability to suppress an effect of allele A.
Feathers color of domestic fowl: Gene 1: allele C = red coloringGene 2: allele I = inhibits an effect of allele C
Phenotype 1: C-I-, ccI-, ccii – colorlessPhenotype 2: C-ii – colored
P
1)x
2)x
F1
CCII ccii CCii ccII
CcIi
C-I- C-ii ccI- ccii 9 : 3 : 3 : 1 13 : 3
F2
Complementarity and Multiplicity
• genes are equal – no subordination• bilateral relation of alleles of interactive genes
Complementarity is bilateral relation of alleles of interactive genes.• Dominant alleles of complementary genes allow
genesis of two or more non-replaceable components, which form the final product.
• Each of these components is qualitatively different and arises from different biosynthetic processes.
• For this reason replacement of any of dominant alleles of complementary genes for recessive one leads to non-formation of the final product.
Complementarity
Flower color of earthnut pea: Gene 1: allele C – formation of colorless precursor Gene 2: allele R – formation of activation enzyme,
which changes the precursor intocolored compound
Phenotype 1: C-R- – red (anthocyan)Phenotype 2: C-rr, ccR-, ccrr – colorless
P
1)x
2)x
F1
CCRR ccrr CCrr ccRR
CcRr
C-R- C-rr ccR- ccrr 9 : 3 : 3 : 1 9 : 7
F2
Multiplicity
is bilateral relation of alleles of interactive genes,but in comparison with complementarity,
each single dominant allele of any of these genes, even in itself, is sufficient for expression of a corresponding trait.
To this effect these single dominant alleles are identical. These alleles are responsible for biosynthesis of identical final products, but by qualitatively different ways.
Multiplicity
• Noncumulative – full expression of a corresponding trait is caused by single dominant allele of given multiplicative rank and presence of next members of the rank no more changes intensity of phenotype.
• Cumulative – intensity of phenotype expression is direct proportionally dependent on number of present dominant members of multiplicative rank.
Duplicity noncumulative
Siliqua shape of shepherd’s purse: Gene 1: allele T1 – normal (heart-shaped)
Gene 2: allele T2 – normal (heart-shaped)
T1+T2 – normal (heart-shaped)
Phenotype 1: T1-T2-, T1-t2t2, t1t1T2- – normal
Phenotype 2: t1t1t2t2 – cylindrical
P
1)x
2)x
F1
T1T1T2T2 t1t1t2t2 T1T1t2t2 t1t1T2T2
T1t1T2t2
T1-T2- T1-t2t2 t1t1T2- t1t1t2t2
9 : 3 : 3 : 1 15 : 1
F2
Duplicity cumulative with dominancecharacter intensity depends on gene number
Caryopsis color of barley: Gene 1: allele P1 – brownish red coloring (half)
Gene 2: allele P2 – brownish red coloring (half)
P1+P2 – dark brown coloring (maximal)
Phenotype 1: P1-P2- – maximal
Phenotype 2: P1-p2p2, p1p1P2- – half
Phenotype 3: p1p1p2p2 – null (white)
P
1)x
2)x
F1
P1P1P2P2 p1p1p2p2 P1P1p2p2 p1p1P2P2
P1p1P2p2
P1-P2- P1-p2p2 p1p1P2- p1p1p2p2
9 : 3 : 3 : 1 9 : 6 : 1
F2
Duplicity cumulative without dominance character intensity depends on allele numberCaryopsis color of wheat: Gene 1: allele R1 – pink coloring (quarter)
Gene 2: allele R2 – pink coloring (quarter)
Phenotype 1: R1R1R2R2 – dark red (maximal)
Phenotype 2: R1R1R2r2, R1r1R2R2 – red (three quarter)
Phenotype 3: R1R1r2r2, R1r1R2r2, r1r1R2R2 – rose (half)
Phenotype 4: R1r1r2r2, r1r1R2r2 – pink (quarter)
Phenotype 5: r1r1r2r2 – white (null)
Davenport’s hypothesis
about pigment synthesis in human:Degree of pigmentation is coded by the number of dominant alleles of 2 allelic pairs / genes
• black - 4 dominant alleles A1A1A2A2• brown - 3 dominant alleles • mulatto - 2 dominant alleles• light brown - 1 dominant allele• white - no dominant allele a1a1a2a2
P A1A1A2A2 x a1a1a2a2
F1 A1a1A2a2
F2
A1A1A2A21
A1A1A2a22
A1A1a2a21
A1a1A2A22
A1a1A2a24
A1a1a2a22
a1a1A2A21
a1a1A2a22
a1a1a2a21
1 : 4 : 6 : 4 : 1
black brown mulatto light brown white
Bilateral allele relation of cooperated genes
Complementarityalleles ≥2 genes
R ∩ S↓ ↓A1 A2↘ ↙
Aphenotype
Multiplicityalleles ≥2 genes
T1 ∪ T2
↘ ↙A
phenotype
GENE INTERACTIONS - SUMMARYGENE INTERACTIONS - SUMMARY
interaction type phenotype cross ratio in the F2 generation
reciprocal interaction 9 3 3 1
dominant epistasis 12 3 1
recessive epistasis 9 3 4
inhibition 13 3
complementarity 9 7
noncumul. duplicity with domin. 15 1
cumul. duplicity with domin. 9 6 1
cumul. duplicity without domin. 1 4 6 4 1
Mendelian inheritance 9 3 3 1
Significance of gene interactions in multifactorial diseases
• the main genetic mechanism of
predisposition to diseases
Principle of cumulative multiplicity = heredity of quantitative traits - polygenic heredity
Significance of gene interactions in monogenic diseases
• low penetrance penetrance = probability of expression of dominant allele in phenotype
- sick or healthy persons
• different expressivity
expressivity= intensity of phenotype manifestation
- severe or minor clinical signs