DO NOWGRAB YOUR GREEN FOLDER. •In golden retrievers, the allele for brown hair is dominant to the allele for yellow hair. If a yellow-haired golden retriever mated with a heterozygous brown-haired retriever, what is the probability that their puppies will be brown haired?

You have 5 minutes.

PUNNETT SQUARES DAY 2NOTES

I CAN…•I CAN make and interpret a Punnett square to predict the genotypes and phenotypes of offspring for sex linked, incomplete, and co-dominant traits

•I CAN interpret a dihybrid cross Punnett square

Can you predict the outcome of 2 traits at the same time?•YES! This is called a dihybrid cross. Just

follow the same Punnett square rules. •On the EOC, you will NOT have to make a

dihybrid cross Punnett Square; you will only have to interpret it correctly.

1.Just figure out who wins the battle in each square, as usual, to determine phenotype

IT’S SO

Dihybrid Punnett Square Cross• Cross between

2 guinea pigs heterozygous for hair color and length

•B=black

•b=white

•S=short

•s=long

Dihybrid Punnett Square Cross

Q: What fraction of the offspring are black and long tailed?

• Cross between 2 guinea pigs heterozygous for hair color and length

•B=black

•b=white

•S=short

•s=long

A:

Q: What fraction of the offspring are white and short tailed?

• Cross between 2 guinea pigs heterozygous for hair color and length

•B=black

•b=white

•S=short

•s=long

A:

Mr. Im lied to me…•There are exceptions to the dominant allele

always winning the battle against the recessive allele that might show up on the EOC1. Incomplete dominance: when two alleles

mix to create a new phenotype2. Co-dominance: when alleles are both

dominant and will both express their phenotypes

•The EOC will always let you know in the question if the trait is incomplete or co-dominant.

Incomplete Dominance: •The alleles for red flower and white flower

petals show incomplete dominance (two alleles mix to create a new phenotype)▫What is the new phenotype? PINK!

Check for UnderstandingQ: In roses the allele for red flowers shows

incomplete dominance with the allele for white flowers. One pink rose and one white rose are crossed. What is the probability of producing a white rose?

Co-dominance•The alleles for white petals and red petals

show co-dominance (alleles are both dominant and will both express their phenotypes)▫Both capital letters.

•What is the phenotype of the flower? Spotted red & white!

Check for UnderstandingQ: A homozygous brown-coated dog is crossed with a brown-and-white-coated dog. Brown and white coats are co-dominant. What is the probability of producing a brown-and-white coated puppy?

Sex Chromosomes

FEMALE: XX MALE: XY

Why are more males colorblind?•Some genes are carried on sex

chromosomes. ▫Sex chromosomes are the X and Y

chromosomesExample: The allele for colorblindness

is recessive and carried on the X chromosome▫XEXE: healthy female▫XeXe: colorblind female▫XEXe: female carrier▫XeY: color blind male▫XEY: healthy male

•It is easier for males to be colorblind, because they only have one X chromosome. One shot and you're done!

E=normal eyese=color blind

Q: Hemophilia (not being able to clot your blood) is a sex-linked recessive disease. A heterozygous female and a male who has hemophilia are worried about having a baby with the disease. What is the probability that they will have a child with hemophilia?

Check for Understanding