1 / 39

Gene Interactions Marie Černá

Gene Interactions Marie Černá. Lecture No 406 - H. Mendelian genetics : 1 character = 1 gene Genes 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.

evanslarry
Download Presentation

Gene Interactions Marie Černá

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Gene InteractionsMarie Černá Lecture No 406-H

  2. Mendelian genetics: 1 character = 1 gene Genes are segregating independently on each other Geneinteractions:1 character = two or more genes Interaction of two genes – genotype ratio as in dihybridism – less phenotype classes

  3. Gene Interactions • Reciprocal interactions • Epistasis - dominant and recessive • Inhibition • Complementarity • Multiplicity

  4. Reciprocal interactions = Interactions without change of phenotype ratio F2: 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

  5. Reciprocal interactions Product color of paprika: Gene 1: allele R – anthocyan = red coloring Gene 2: allele Cl – chlorophyll degradation = yellow pigment Phenotype 1: R-Cl- – red (anthocyan) Phenotype 2: R-clcl – brown (red + green) Phenotype 3: rrCl- – yellow Phenotype 4: rrclcl – green (chlorophyll)

  6. 1) 2) x x P RRClCl rrclcl RRclcl rrClCl F1 RrClcl F2 R-Cl- R-clcl rrCl- rrclcl 9 : 3 : 3 : 1

  7. 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)

  8. 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.

  9. Dominant Epistasis Flower color of dahlia: depends on hydroxylation degree of colorless precursor of flavon pigment Gene 1: allele Y – higher degree = dark yellow Gene 2: allele I – lower degree = light yellow (ivory white) Phenotype 1: Y-I-, Y-ii – dark yellow Phenotype 2: yyI- – light yellow Phenotype 3: yyii – white

  10. 1) 2) x x P YYII yyii YYii yyII F1 YyIi F2 Y-I- Y-ii yyI- yyii 9 : 3 : 3 : 1 12 : 3 : 1

  11. 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 coloringgene 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

  12. 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?

  13. 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

  14. 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?

  15. Recessive Epistasis • Recessive allele of one gene in 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.

  16. Recessive Epistasis Flower color of sage: depends on hydroxylation degree of colorless precursor of flavon pigment Gene 1: allele P – lower degree = rose coloring Gene 2: allele A – higher degree = violet coloring Phenotype 1: P-A- – violet Phenotype 2: P-aa – rose Phenotype 3: ppA-, ppaa – white

  17. 1) 2) x x P PPAA ppaa PPaa ppAA F1 PpAa F2 P-A- P-aa ppA- ppaa 9 : 3 : 3 : 1 9 : 3 : 4

  18. 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 alleleshh = Bombay allele transferase H transferase A transferase B hh 0

  19. 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

  20. Epistasis- unilateral relation • Dominant substrate Y -------> P1 I -------> P2 • Recessive substrate BA -------> P0-------> P

  21. Inhibition It 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 coloring Gene 2: allele I = inhibits an effect of allele C Phenotype 1: C-I-, ccI-, ccii – colorless Phenotype 2: C-ii – colored

  22. 1) 2) x x P CCII ccii CCii ccII F1 CcIi F2 C-I- C-ii ccI- ccii 9 : 3 : 3 : 1 13 : 3

  23. Complementarity and Multiplicity genes are equal – no subordination bilateral relation of alleles of interactive genes

  24. 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.

  25. 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 into colored compound Phenotype 1: C-R- – red (anthocyan) Phenotype 2: C-rr, ccR-, ccrr – colorless

  26. 1) 2) x x P CCRR ccrr CCrr ccRR F1 CcRr F2 C-R- C-rr ccR- ccrr 9 : 3 : 3 : 1 9 : 7

  27. 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.

  28. 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.

  29. 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

  30. 1) 2) x x P T1T1T2T2 t1t1t2t2 T1T1t2t2 t1t1T2T2 F1 T1t1T2t2 F2 T1-T2- T1-t2t2 t1t1T2- t1t1t2t2 9 : 3 : 3 : 1 15 : 1

  31. 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)

  32. 1) 2) x x P P1P1P2P2 p1p1p2p2 P1P1p2p2 p1p1P2P2 F1 P1p1P2p2 F2 P1-P2- P1-p2p2 p1p1P2- p1p1p2p2 9 : 3 : 3 : 1 9 : 6 : 1

  33. Duplicity cumulative without dominancecharacter intensity depends on allele number Caryopsis 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)

  34. 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

  35. P A1A1A2A2 x a1a1a2a2 F1 A1a1A2a2 F2 A1A1A2A2 1 A1A1A2a2 2 A1A1a2a2 1 A1a1A2A2 2 A1a1A2a2 4 A1a1a2a2 2 a1a1A2A2 1 a1a1A2a2 2 a1a1a2a2 1 1 : 4 : 6 : 4 : 1 black brown mulatto light brown white

  36. Bilateral allele relation of cooperated genes Complementarity alleles ≥2 genes R ∩ S ↓ ↓ A1 A2 ↘ ↙ A phenotype Multiplicity alleles ≥2 genes T1∪ T2 ↘ ↙ A phenotype

  37. GENE 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

  38. 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

  39. 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

More Related