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 in Dihybrid Crosses T T Y Y TY

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

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

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

Dihybrid crosses involve 2 traits

P Generation P Gametes F1 Generation

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

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 TtRW TW Phenotype of offspring: all Tall & Pink Genotype of offspring: TtRW

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

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 rB RRBB RrBb RrBB RRBb

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. Phenotypic Ratio 1:1:1:1 Genotypic Ratio 1:1:1:1 bC bc Bc bc BbCc Bbcc bbCc bbcc C = crested c = plain B = black b = red Parental Genotypes bbCc & Bbcc

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

Trihybrid Cross YIKES!!

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

Lethal Alleles Dominant allele is Lethal!

Mexican hairless dog!! Hh

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

Example: Coat color in dogs B = black coat b = brown coat ALSO 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 2. Epistatic Interaction Genes that mask the expression of other genes

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

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

Walnut Rose Pea Single

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!!

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

Walnut Rose Pea Single

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!)Sickle cell disease

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

Normal & Abnormal Red Blood Cells

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

Marfan’s Syndrome

Abraham Lincoln Symptoms of Marfan’s??

Marfan’s Syndrome Long thin limbs & Abnormal joints

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

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

Sun lightens hair & Darkens freckles

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