DO NOW1. Complete a punnett square

showing the cross between a heterozygous tall plant and a homozygous recessive plant .

ANNOUNCEMENTS• Gonzaga is now ranked • Quiz on Thursday• I will not be here on Friday.

AGENDA• Sex linked traits• Sex linked punnett squares• Article detailing sex linked

traits

SEX LINKED TRAITS• Sex linked traits are those

traits that are found on either the X or Y chromosome.

HEMOPHILIA• Hemophilia is a disease

where your blood doesn’t clot.

• It only occurs when all of the X chromosomes have a copy of the recessive gene.

SEX LINKED TRAIT EXAMPLE

• XHXh: Female Carrier• XhXh: Female Hemophiliac• XHY: Normal Male• XhY: Hemophiliac Male

SEX LINKED TRAIT PUNNETT SQUARE

• As we’re watching this video, let’s copy this professor’s example in our notes.

• http://www.youtube.com/watch?v=j35OALtS3Bk

EXAMPLE• Colorblindness is inherited as a sex-

linked recessive disease. An affected male marries a heterozygous female. Draw a Punnett square of the possible offspring. What is the chance that they will have an affected child? Could any of their daughters be affected?

EXAMPLEColorblindness is inherited as a sex-linked recessive disease. 1. Recognize how the disease in inherited.a. Sex-linked means that the gene is carried on the X chromosome. b. Recessive means that both alleles must be recessive for female to have the disease. Females could have a good backup copy because they have two X chromosomes. c. Males, who only have one X chromosome, will have the disease if their only X is mutant.

EXAMPLEAn affected male marries a heterozygous female. 2. Determine the genotypes of the parents.Affected male is XA Y (since he is affected, his only X is mutant)Heterozygous female is XA X (heterozygous means one of each allele)

EXAMPLE

Draw a Punnett square of the possible offspring.3. Set up the Punnett square with the genotypes of the above two parents. 

EXAMPLEWhat is the chance that they will have an affected child? 4. Determine how many possibles would be affected according to how the disease in inherited (See help #1).