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Dihybrid Crosses Involve 2 traits

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Presentation on theme: "Dihybrid Crosses Involve 2 traits"— Presentation transcript:

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 ty TY Ty tY TY Ty tY ty Dihybrid Cross TtYy X TtYy 9:3:3:1 Pheno Ratio

6 Dihybrid crosses involve 2 traits

7 P Generation P Gametes F1 Generation

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

9 ttRR TTWW tR TW Gametes from Parents tR X TW
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 Dwarf, red snapdragon ttRR Genotype of Homozygous Tall white snapdragon TTWW Gametes from Parents tR X TW tR Phenotype of offspring: all Tall & Pink Genotype of offspring: TtRW TW TtRW

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

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13 RB Rb RB rB RRBB RRBb RrBB RrBb 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

14 bC bc Bc bc Phenotypic Ratio Genotypic Ratio 1:1:1:1 1:1:1:1 Parental
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 Bc BbCc Bbcc bc bbCc bbcc Phenotypic Ratio 1:1:1:1 Genotypic Ratio 1:1:1:1

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

16 Trihybrid Cross YIKES!!

17 2n where n = number of different
Working out Gametes!! 2n where n = number of different sets of alleles n= 1 for mono n= 2 for dihybrid n= 3 for trihybrid

18 Lethal Alleles Dominant allele is Lethal!

19 Mexican hairless dog!! Hh

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

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

22 Dog example continued yellow/white wwBb genotype = ______ phenotype
black Yellow/white brown yellow/white brown black

23 4 Yellow/white:3 Black: 1 Brown
What would be the genotypes and phenotypes produced by a cross between two dogs: WwBb x wwBb? wB wb WB WwBB WwBb Wwbb wwBB wwBb wwbb Wb wB wb 4 Yellow/white:3 Black: 1 Brown

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

25 Walnut Rose Pea Single

26 Question on Complimentary 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!!

27 RP Rp rP rp RP Rp rP rp Dihybrid Cross RrPp X RrPp 9:3:3:1 Pheno Ratio

28 Walnut Rose Pea Single

29 Pleiotropic Genes Example 1: Sickle Cell disease
A gene that affects many characteristics throughout body Example 1: Sickle Cell disease HbAHbA= normal hemoglobin HbSHbS = sickle cell anemia mutations can lead to fatigue and weakness, enlarged spleen, rheumatism, pneumonia HbAHbS = Resistance to malaria (sickle cell trait)

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

31 Normal & Abnormal Red Blood Cells

32 Example 2: Marfan’s Syndrome
Long thin limbs & Abnormal joints Example 2: Marfan’s Syndrome inability to produce connective tissue eye, skeleton and cardiovascular defects show up

33 Abraham Lincoln Symptoms of Marfan’s??

34 Environment and Phenotype
Examples: Primrose flowers Red if raised at room temp White when raised above 30 0 C

35 Effect of Environment on Phenotype
2. Water Plants Submerged leaves are finely divided, Compared with the ones Growing in air

36 3. Sun lightens hair & darkens freckles

37 Genetics Problems 1:Dihybrid crosses
Practice Genetics Problems More Practice!


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