punnett squares :

Genetics Notes Day 2

Warm Up – What is the difference between a genotype and a

phenotype? Give an example of each.

Bring in your PHOTOS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

We are doing “Throw Back Thursday” this week!

A diagram that predicts the expected outcome of a genetic cross.

Helps you keep track of traits.

Punnett Squares

.

Dominant and recessive alleles

are represented by letters.

Punnett Squares

A capital letter (T) is used for dominant alleles.

Punnett Squares

A lowercase letter (t) is used for recessive alleles.

Punnett Squares

Example (Tall or short)

T = dominant allele t = recessive allele Homozygous dominant

– Genotype = _____ Phenotype = __________

Heterozygous– Genotype = _____ Phenotype = __________

Homozygous recessive– Genotype = _____ Phenotype = __________

If you wanted to know the type of offspring a cross between two parents would produce, you can use a punnett square.

Tt x Tt

TT,Tt for tall

Tt for short

Punnett Squares

The letters representing the alleles from one parent are placed along the top of the square.

T t

Punnett Squares

The letters representing the two alleles from the second

Parent are places along the side of the square.

T

t

Punnett Squares

T t x T t

T t

T

t

Punnett Squares

Punnett Squares

Squares are filled by writing the letter at the top beside the letter on the side.

TT Tt

Tt t t

T t

T

t

Punnett Squares

The letters in each of the squares represents the Genotypes of the offspring that the parents could produce.

TT Tt

Tt t t

T t

T

t

TT

Tt

Tt

t t

The genotype (genetic makeup) can be used to predict the phenotype (physical appearance) of the offspring.

Punnett Squares

Genotype Phenotype

TT tall

Tt tall

Tt tall

t t short

Punnett Sqaures

Punnett Squares

Probability: the ratio that a particular event could occur.

out of 4 offspring3 would be tall

1 would be short

Punnett Squares:

•Help you keep track of traits.

•Predict genotype and phenotype.

•Calculate probability.

Bb Bb

Bb Bb

BB x bb

b b

B

B

Genotypes: Bb, Bb, Bb, Bb

Phenotypes: All brown

Probability: 100%

BB Bb

BB Bb

BB x Bb

B b

B

B

Genotypes: BB, BB, Bb, Bb

Phenotypes: All brown

Probability: 100% brown

Genetics Notes Day 3

Warm Up: Create a Monohybrid cross from these parents:

Dad = heterozygous for Brown Eyes

Mom = homozygous recessive for Blue Eyes

Bb bb

Bb bb

B b

b

b

Dihybrid Crosses

A cross that involves two pairs of contrasting traits.

– RrYy crossed with RrYy

– RY Ry rY ry – RY Ry rY ry

BBff x BBFF

• Bf Bf Bf Bf

• BF BF BF BF

Ttrr x ttRr

• Tr Tr tr tr

• tR tr tR tr