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Dihybrid Crosses

Dihybrid Crosses. Involve 2 traits Eg. Crossing tall yellow pea plants with short green pea plants Procedure is same as with monohybrids Must first find gametes Then cross in punnett square Then show gametes coming together , making offspring!. Working out Gametes

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Dihybrid Crosses

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  1. Dihybrid Crosses • Involve 2 traits • Eg. Crossing tall yellow pea plants with short green pea plants • Procedure is same as with monohybrids • Must first find gametes • Then cross in punnett square • Then show gametes coming together, making offspring!

  2. Working out Gametes in Dihybrid Crosses T T Y Y TY TY TY TY

  3. Working out Gametes in Dihybrid Crosses T t Y Y TY tY tY TY

  4. Working out Gametes in Dihybrid Crosses T t Y y Ty ty tY TY

  5. TtYy X TtYy ty tY TY Ty TTYy TTYY TY TtYy TtYY 9:3:3:1 Pheno Ratio TTyy TTYy Ty Ttyy TtYy ttYy TtYY ttYY tY TtYy ttyy TtYy Ttyy ty ttYy Dihybrid Cross

  6. Dihybrid crosses involve 2 traits

  7. P Generation P Gametes F1 Generation

  8. Predict the phenotypic outcome if a hetero tall, homozygous yellow pea plant is crossed with TTYY tY TY TTYY TtYY TY TY TTYY TtYY Genotypes 2 TTYY & 2 TtYY Phenotypes All Tall &Yellow

  9. A dwarf, red snapdragon is crossed with a homozygous tall white plant. Determine the pheno and geno of the F1’s. (Tall is dom, red incompletely dom to white) Genotype of Homozygous Tall white snapdragon TTWW Genotype of Dwarf, red snapdragon ttRR Gametes from Parents tR X TW tR Phenotype of offspring: all Tall & Pink Genotype of offspring: TtRW TtRW TW

  10. Summary of Dihybrid Cross • Most complex punnett square involves 2 parents heterozygous for both traits • eg. RrBb X RrBb • 4 possible gametes from each parent • Punnett square is 4 X 4 • Classic 9:3:3:1 phenotypic ratio in offspring

  11. If parents are RRBb and RrBB….. • Only 2 possible gametes from each parent (RB or Rb) and (RB or rB) • Punnett square becomes 2 X 2 instead of 4 X 4! Rb RB RB RRBB RRBb rB RrBb RrBB

  12. In poultry, a crested head is produced by a dom. allele and a plain head by it’s rec allele. Black feather is dom to red. A homozygous red feathered, hetero. crest headed bird is mated to a hetero. black, plain headed bird! Find the pheno’s and geno’s of the F 1’s. bc bC Parental Genotypes bbCc & Bbcc C = crested c = plain B = black b = red BbCc Bc Bbcc bc bbCc bbcc Phenotypic Ratio 1:1:1:1 Genotypic Ratio 1:1:1:1

  13. Gametes would be abc & ABC All offspring: AaBbCc Gametes would be ABC, AbC, aBC, abC ABc, Abc, aBc, abc

  14. Trihybrid Cross YIKES!!

  15. Working out Gametes!! 2nwhere n = number of different sets of alleles n= 1 for mono n= 2 for dihybrid n= 3 for trihybrid

  16. Lethal Alleles Dominant allele is Lethal!

  17. Mexican hairless dog!! Hh

  18. Gene Interaction 1.Polygenic Inheritance • Where a trait is controlled by more than one gene • Skin color • Eye color • Height

  19. W = prevents pigment w = does not prevent color ALSO • Example: Coat color in dogs • B = black coat • b = brown coat W is a separate gene located on a separate chromosome W allele masks the effect of the B gene 2. Epistatic Interaction Genes that mask the expression of other genes

  20. Dog example continued black • wwBb genotype = ______ phenotype • WwBb genotype = ______ phenotype • wwbb genotype = _______ phenotype white brown

  21. Genotype B + = 3. Complementary Interaction • Occurs when two genotypes combine to create a phenotype that neither can produce alone Genotype A Phenotype C Chicken Example R = rose comb P = pea comb R + P = walnut r + p = single comb

  22. Rose Pea Walnut Single

  23. Question onComplimentary Interaction • Find the F1’s and the F2’s for the following parents: • RRpp x rrPP • Gametes would be Rp x rP • All offspring would be RrPp • Phenotype: all walnut • Must use punnett square for second cross!!

  24. RrPp X RrPp rp rP RP Rp 9:3:3:1 Pheno Ratio RRPp RRPP RP RrPp RrPP RRpp RRPp Rp Rrpp RrPp rrPp RrPP rrPP rP RrPp rrpp RrPp Rrpp rp rrPp Dihybrid Cross

  25. Rose Pea Walnut Single

  26. Pleiotropic Genes • Affect many characteristics throughout body • Sickle Cell Anemia • mutations can lead to fatigue and weakness, enlarged spleen, rheumatism, pneumonia • Sickle cell disease (easy to follow info!)

  27. Notice sickle shape of cells…can’t carry enough oxygen & get stuck in caps Blood smear showing sickle cell anemia

  28. Normal & Abnormal Red Blood Cells

  29. Pleiotropic Genes • Eg. Marfan’s Syndrome • inability to produce connective tissue • eye, skeleton and cardiovascular defects show up

  30. Marfan’s Syndrome

  31. Abraham Lincoln Symptoms of Marfan’s??

  32. Marfan’s Syndrome Long thin limbs & Abnormal joints

  33. Environment and Phenotype • Primrose flowers • Red if raised at room temp • White when raised above 30 0 C

  34. Effect of Environment on Phenotype Submerged leaves are finely divided, Compared with the ones Growing in air

  35. Sun lightens hair & Darkens freckles

  36. Genetics Problems 1:Dihybrid crosses Practice Genetics Problems More Practice!

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