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Additional Genetic Patterns

Additional Genetic Patterns . Additional Genetic Patterns . RR x R’R’ Red White. RR’ pink. Incomplete Dominance . Incomplete dominance: neither allele masks the other and both are observed as a blending in the heterozygote. Four o’clock flowers R = red, R’ = white.

Samuel
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Additional Genetic Patterns

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  1. Additional Genetic Patterns

  2. Additional Genetic Patterns

  3. RR x R’R’ Red White RR’ pink Incomplete Dominance Incomplete dominance: neither allele masks the other and both are observed as a blending in the heterozygote Four o’clock flowers R = red, R’ = white

  4. ½ R ½ R’ ½ R ½ R’ Incomplete Dominance RR’ x RR’ Pink x Pink ¼ RR ¼ RR’ ¼ RR’ ¼ R’R’ Genotypic Ratio: ¼ RR + ½ RR’ + ¼ R’R’ Phenotypic Ratio: ¼ red + ½ pink + ¼ white

  5. Multiple Alleles • Multiple alleles: three or more alleles exist for one trait (Note: A diploid individual can only carry two alleles at once.)

  6. Codominance Codominance: Neither allele masks the other so that effects of both alleles are observed in heterozygote without blending IA =IB > i IA and IB are codominant. IA and IB are completely dominant over i.

  7. Codominance

  8. IAi IBi Antigens on Red Blood Cells IAIB

  9. Inheritance of Rh Factor *There are multiple alleles for the Rhesus protein (R1, R2, R3, etc.) and all are dominant to the multiple alleles for the absence of Rhesus protein (r1, r2, r3, etc.) .

  10. Multiple Alleles and Codominance Type A, Rh positive x Type B, Rh negative (father is Type O, Rh negative) (mother is Type O) IB irr IA iRr x IAR IAr iR ir IBr ir IAIBrr IBiRr IBirr IAIBRr IAirr iiRr iirr IAiRr Phenotypic Ratio of Offspring 1/8 Type AB positive 1/8 Type A positive 1/8 Type AB negative 1/8 Type A negative 1/8 Type B positive 1/8 Type O positive 1/8 Type B negative 1/8 Type O negative

  11. ½ ML ½ m X ½ ML ½ m 2/3 tailless + 1/3 tails Lethal Alleles Example: Manx cat ML = tailless, lethal in homozygote m = tail Tailless male x Tailless female MLm x MLm ¼ MLML ¼ MLm dies tailless ¼ mm ¼ MLm tailless tail

  12. Hierarchy of Dominance Example: hair curling Sw = wooly Sc= curly Swa= wavy s = straight Sw>Sc> Swa>s

  13. Hierarchy of Dominance Sw>Sc> Swa>s Dad Colavito has wavy hair. Mom Colavito has curly hair. Their daughter Jean has straight hair. What are the expected genotypic and phenotypic ratios for their offspring?

  14. ½ Sc ½ s ½ Swa ½ s Hierarchy of Dominance Sw> Sc> Swa>s Dad C x Mom C Wavy Curly Swas Scs ¼ Swas ¼ ScSwa curly wavy ¼ Scs ¼ ss curly straight Bonus: What is Dr. C’s genotype?

  15. Pleiotropic Effects One gene affects many phenotypic characteristics

  16. Example of Polygenic Inheritance Two genes affecting skin coloration *Based on a study conducted in Jamaica.

  17. Polygenic Inheritance Medium Black Woman (mother is white) X Darkest Black Man AaBb AABB AB Ab aB ab AABb AaBB AaBb AB AABB Dark Black Dark Black DarkestBlack Medium Black ¼ Darkest Black + ½ Dark Black + ¼ Medium Black

  18. Interacting Genes Affecting a Single Characteristic eg. Skin coloration in snakes One gene O = orange pigment o = no orange pigment Second gene B= black pigment b = no black pigment

  19. Interacting Genes Affecting a Single Characteristic eg. Skin coloration in snakes Oo Bb x Oo Bb OB Ob o b o B OB Ob o B o b

  20. Interacting Genes Affecting a Single Characteristic eg. Skin coloration in snakes OoBb x OoBb 9/16 O_B_ camouflaged 3/16 O_bb orange 3/16 ooB_ black 1/16 oobb albino

  21. Epistasis • An allele of one gene masks the expression of alleles of another gene and expresses its own phenotype instead. • Gene that masks = epistatic gene • Gene that is masked = hypostatic gene • Genes that code for enzymes that are upstream in a biochemical pathway usually exert epistasis (“standing on”).

  22. W M enzyme 1 enzyme 2 Precursor 1 Precursor 2blue anthocyanin colorless magenta Recessive Epistasis Epistatic gene exerts its affect with homozygous recessive genotype. eg. Petal color in blue-eyed Mary plants mm= magenta, ww =white, W__M__= blue

  23. Recessive Epistasis eg. Petal color in blue-eyed Mary plants Ww Mm x Ww Mm 9/16 W__ M__ 3/16 W __mm 3/16 w w M__ 1/16 w w mm Blue Magenta White White Phenotypic ratio: 9/16 blue: 3/16 magenta: 4/16 white

  24. W B enzyme 1 enzyme 2 Duplicate Recessive Epistasis Defective products of recessive alleles of two different genes interfere with separate steps in a biochemical pathway. eg. Petal color in harebell flowers ww = white, bb = white, W_ B_ = blue Precursor 1 Precursor 2blue anthocyanin colorless colorless

  25. Duplicate Recessive Epistasis eg. Petal color in harebell flowers Ww Bb x Ww Bb 9/16 W__B__ 3/16 W __b b 3/16 w w B__ 1/16 w w bb Blue White White White Phenotypic ratio: 9/16 blue: 7/16 white

  26. Dominant Epistasis Epistatic gene exerts its affect with the presence of a dominant allele. eg. Fruit color in summer squash Y = yellow, yy = green; W inhibits either color = white; w has no effect on color

  27. Dominant Epistasis eg. Fruit color in summer squash Ww Y y x Ww Y y 9/16 W__ Y__ 3/16 W __yy 3/16 w w Y__ 1/16 w w yy White White Yellow Green Phenotypic ratio: 12/16 white: 3/16 yellow: 1/16 green

  28. Duplicate Dominant Epistasis eg. Fruit shape in Shepherd’s purse A_ or B_ = heart shape aa and bb = narrow shape

  29. Duplicate Dominant Epistasis eg. Fruit shape in Shepherd’s purse A_ or B_ = heart aa and bb = narrow A a Bb x A a Bb 9/16 A__B__ 3/16 A__b b 3/16 aa B__ 1/16 aa b b heart heart heart narrow Phenotypic ratio: 15/16 heart: 1/16 narrow

  30. Interaction between Sex and Heredity John Adams John Quincy Adams Male pattern baldness Dominant in males, recessive in females

  31. Interaction between Sex and Heredity Cock-feathered male Hen-feathered female Hen-feathered male Cock feathering, autosomal recessive Expressed only in males

  32. Interaction betweenSex and Heredity Leaf variegation caused by inheritance of variable chloroplast genotypes

  33. Interaction betweenSex and Heredity Direction of snail shell coiling is determined by genotype of female parent

  34. Interaction Between Sex and Heredity Angelman SyndromeDeletion on chromosome 15 inherited from mother Prader-Willi SyndromeDeletion on chromosome 15 inherited from father

  35. Anticipation Trait is more strongly expressed or expressed earlier in succeeding generations

  36. Expansion of the Trinucleotide Repeat for Huntington’s Disease Linda (6,22) Allen (46,13) age 50 Jama (7,18) Andrew (69,6) age 37 Kristen (64,22) age 40 Ann (64,22) age 39 Bill (8,12) Greg (11,19) Debbie (13,6) Christina (93,7) age 26 Joseph (7,6) Nathaniel (72,19) age 35 Paula (13,12) Evan (not tested)

  37. Environmental Effects Phenotype is dependent upon the presence of a specific environment. The temperature-sensitive product of the himalayan allele is inactivated at high temperatures.

  38. Penetrance and Expressivity • Penetrance = percentage of individuals with a given genotype who exhibit the phenotype • Expressivity = extent to which genotype is expressed at the phenotypic level (may be due to allelic variation or environmental factors)

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