1. Blood Types & Sex-Linked Traits
Biology Honors

2. Multiple Alleles
Blood Types

3. Multiple Alleles Traits are the result of more than 2 types of alleles
Example: blood typing
There are 3 different alleles for blood type (A, B, & O)
A is dominant to O
B is also dominant to O
A and B are both codominant

4. Blood Transfusions
Blood can only be transferred to a body of a person who's immune system will "recognize" it.
Type A = A antigens
Type B = B antigens
Type O = No antigens
O is the universal donor
a person can receive a transfusion from O blood without having an immune response
AB is the universal recipient
because a person with AB blood has both the A and B antigens already in the body

5. Multiple Alleles

6. Sample Crosses

7. Sex-Linked Traits

8. Sex-linked Traits
A gene that is found only on the X chromosome and not the Y chromosome
Examples:
Colorblindness
Hemophilia
Duchenne Muscular Dystrophy
Male Pattern Baldness
Female Male

9. Sex-linked Traits
More common in men because they only have one X chromosome
Females need to have the gene on both X’s to have the trait
Females that are heterozygous for the trait are carriers
Carriers appear normal but can pass the trait to their offspring

10. Colorblindness Recessive trait on X chromosome
Condition in which certain colors cannot be distinguished
Red/Green color blindness is most common (about 99%)
Causes problems in distinguishing reds and greens
No treatment
Life is normal

11. Hemophilia Recessive trait on the X chromosome
Bleeding disorder in which the blood does not clot normally
Persons with hemophilia may bleed for a longer time than others after an injury or accident
They also may bleed internally, especially in the joints
Live life cautiously, receive treatments to help blood clot normally

12. Duchenne Muscular Dystrophy
Caused by a recessive gene on the X chromosome
Rapidly-worsening muscle weakness that starts in the legs and pelvis, and later affects the whole body
No cure
Treatment is aimed at control of symptoms to maximize the quality of life
Death usually occurs by age 25

13. How to do a sex-linked cross

14. Sample Problem: Male Pattern Baldness
Unlike all the other crosses there is information that we know before we ever read the problem. We know that a XX female is going to mate with a XY male. So, you can set up your square ahead of time.
X Y XX XY
X X

15. Next, you have to read the problem and figure out what the sex-linked condition is and write down the allele you want to use for the problem and set up a key!
Baldness is a sex-linked trait. The allele for baldness is recessive and is carried on the X chromosome. The Griffin family lives in a town called Quahog. The father, Peter, has a gene for normal hair. The wife, Lois, is a carrier for baldness. Peter and Lois have 3 kids: Chris, Meg, and Stewie. The kids want to know what is the probability they will develop baldness?

16. Setting up your key What letters will Peter have since he is a male?XY
What letters will Lois have since she is a female? XX
Decide what letter you will use for the trait
B = normal, b= bald

17. Reread the problem and find the parents genotypes using the key you just made
So, Peter is XY and Lois is XX
Now you have to add the allele for baldness to all of the X chromosomes as described in the problem
Peter XBY
Lois XBXb

18. Now, set up the Punnett square and do the cross…Don’t forget the genotype and phenotype ratios!

19. XB Y XB Xb Geno: ¼ XBXB ¼ XBXb ¼ XBY ¼ XbY Pheno: ¼ female, normal
¼ female, carrier
¼ male, normal
¼ male, bald

20. Answer the question:
What is the probability the children will develop baldness?
Females = 0% chance
Males = 50% chance