PUNNETT SQUARES

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PUNNETT SQUARES

Punnett Square: A diagram that is used to predict the outcome of a cross between organisms

They show the results of any cross

Target: I will be able to use Punnett Squares to predict the phenotype and genotype ratio of crosses involving one trait.

Pg. 25

Practice: Cross a homozygous purple plant and a homozygous white plant.

PPp

p

Pp Pp

Pp Pp

• Genotypes: 1:1 Pp (100% Pp)

• Phenotypes: 1:1 Purple (100% Purple)

Hybrid Cross: A cross between two hybrids (Heterozygotes).

Practice: Cross a heterozygous Tall plant and a Heterozygous Tall Plant. Note tall (T) is dominant over short (t)

TtT

t

TT Tt

Tt tt

• Genotypes: 1TT :2Tt :1tt• Phenotypes: 3 Tall: 1 Short

Test Cross: an individual of unknown genotype is mated with an individual showing the contrasting recessive trait.   Dihybrid Cross: When there are two heterozygous traits that we are looking at. How to Solve a Dihybrid Cross: 1. Determine the parent genotypes, unless given 2. Determine the gametes using the FOIL method

3. Set up a large 4x4 Punnett Square, place one gamete set from the parent on the top, and the other on the side

4. Solve like a typical Punnett Square but put the same letters together (TTGG; not TGTG)

Example- How to FOIL a Genotype to Determine Gametes:

Parent Genotype: TtGg Tall = T Short = t Green = G yellow = g T t G g       TG Tg tG tg

Summary:

PUNNETT SQUARE PRACTICESeed Shape = Round (R)/Wrinkled (r)

Rr x RR

Seed shape = Round (R)/Wrinkled (r)

Rr x Rr

Plant Color = Green (G)/Yellow (g)

GG x gg

Pg. 26

Plant Color = Green (G)/Yellow (g)

Gg x gg

Plant height= Tall (T)/Short (t)

Tt x TT

Plant height= Tall (T)/Short (t)

Tt x Tt

Predict the offspring of this dihybrid cross: YyRr x YyRr

(Y = Yellow Seed, y = Green Seed), R = Round, r = Wrinkled)

For each Punnett Square- be sure to write the genotype ratios and phenotype ratios off to the side!!