notes

1. Assign Yourself: Sex Linked Practice
• Do Now:
• Unit 2 Review 1 through 11 (yes, you may use
your homework)

2. Sex-Linked Inheritance

3. What is sex-linked inheritance?
• Patterns seen when alleles for a trait are carried on
the X chromosome.
XA = X chromosome with dominant allele
Xa = X chromosome with recessive allele
• Y chromosomes do NOT carry the alleles.

4. Processing Piece:
• Draw a picture to illustrate sex-linked inheritance.
• Find these on your paper:
XAXa XAY XaXa XaY
• Label each one as a boy or girl.
• Label each one as recessive or dominant trait.

5. What is a carrier?
• A person who carries ONE allele for a recessive trait
but does NOT show the recessive trait.
• Sometimes they’re shown on a pedigree like this:
= female carrier

6. Processing Piece:
• Label the carriers.
XAXa XAY XaXa XaY

7. Processing Piece:
On the pedigree below, label each person as XX or XY.
Circle X chromosomes with the recessive allele (Xa)

8. Processing Piece:
What patterns do you notice? Who are the carriers?
Who are the people affected?

9. What patterns are seen in sex-linked
inheritance?
• Females who are carriers (heterozygous)
• Males with the recessive trait

10. Sample Questions 1 through 3:
1) Are most affected
individuals male?
2) Are most carriers
female?
3) Do you think this
is sex-linked
inheritance?

11. Sample Questions 4 through 5:
4) Are most affected individuals male?
5) Are most carriers female?
6) Do you think this is sex-linked inheritance?

12. Sample Question 7
A family has 2 parents, 1 son and 1 daughter. The father is
colorblind (a sex-linked trait), and the mother does not carry
any alleles for it. XN = normal Xn = colorblind
a) What is the father’s genotype? _________
b) What is the mother’s genotype? _________
c) What must the daughters’ genotypes be?__________
d) What must the sons’ genotypes be? ______________
e) Draw a pedigree of this family.

13. Sample Question 8
A woman who is a carrier marries a man who has hemophilia.
XN = normal Xn = hemophilia
a) Genotypes of the parents? _________ x _________
b) Draw a Punnett Square:
c) A boy who has hemophilia? ___
d) A girl who is a carrier? ____
e) A boy who does NOT have hemophilia? _______
f) a girl who is NOT a carrier? ____

14. #4 on the classwork

15. Exit Ticket
1) Which chromosome, X or Y, carries the alleles in
sex-linked inheritance?
2) What are 2 patterns that are normally seen in
sex-linked inheritance?
3) Draw an example of a pedigree you might see
for a sex-linked trait.

16. Assign Yourself: Draw and color completely
(no white spots!) 2 parents and 2 dragon
babies
• Do Now:
• Unit 2 Review 12-23

17. Exit Slip
• Describe the pilot program that some schools
in Kentucky participated in. Why was it
started? Explain whether or not you think the
program is a good idea and why. Support your
response with information from the article.