1. The deadline for all missing assignments is Friday, March 8 at 3:30.

2. Chromosomes and Inheritance

3. Describe sex linked inheritance.
Learning Objectives
Describe sex linked inheritance.

4. Karyotypes
This karyotype shows a diploid set of human chromosomes.

5. Sex Chromosomes
Two of the chromosomes in the human genome are sex chromosomes.
Females: XX
Males: XY

6. Autosomal Chromosomes
The non-sex chromosomes are called autosomes.

7. Notation XA = dominant Xa = recessive Y = male chromosome
Sex-Linked Genes
Males have only 1 X, so all x-linked alleles are expressed
Colorblindness
Hemophilia
Notation
XA = dominant
Xa = recessive
Y = male chromosome

8. Where do females get their X chromosomes?
One from mom, one from dad.
Where do males get their X chromosome?
From mom
Where do males get their Y chromosome?
From dad
Who determines the sex of the baby, the mom or the dad?
The dad

9. Is the mother color blind?
Color blindness is a recessive genetic disorder that is carried on the X chromosome. Answer the following questions about the family of a baby boy who was born with this disorder.
Is the mother color blind?
You don’t know, but probably not.
Is the father color blind?
You don’t know, but probably not. If he is, it’s a coincidence.
Did the boy get the disorder from his mom or his dad?
Mom

10. Color blindness is a recessive genetic disorder that is carried on the X chromosome. A little girl from a different family is colorblind.
Is her mother colorblind?
Don’t know, probably not
Is her father colorblind?
Yes
Did the girl get the disorder from her mom or her dad?
Both

11. XAXa x XaY 1/4 Xa Y Xa Xa Xa Y XA XA Xa XA Y
Mom is heterozygous for colorblindness.
Dad is colorblind
The mom is pregnant. She does not know anything about the baby yet. What are the chances that she will have a colorblind daughter?
XAXa x XaY
1/4 Xa Y
Xa Xa
Xa Y XA
XA Xa
XA Y

12. Vitamin D-resistant rickets is a dominant genetic disease that is carried on the X chromosome. Answer the following questions about the family of a baby boy who was born with this disease
Does the mother have D- resistant rickets?
Yes
 Does the father have D-resistant rickets?
Don’t know, probably not. If he does, it’s a coincidence.
Did the boy get the disease from his mom or his dad?
Mom 

13. Vitamin D-resistant rickets is a dominant genetic disease that is carried on the X chromosome. A normal woman and a man with rickets have a daughter. What are the chances that the girl has rickets? Use a Punnett square to justify your answer.
100% XA Y Xa
Xa XA
Xa Y

14. Hemophilia is caused by a X-linked recessive allele
Hemophilia is caused by a X-linked recessive allele. A normal woman (whose father had hemophilia) marries a man with hemophilia. What fraction of their children are expected to be girls with hemophilia? Use a Punnett square to justify your answer.
25% Xa Y
Xa Xa
Xa Y XA
XA Xa
XA Y

15. A pedigree chart shows the relationships within a family.

16. Hemophilia – Sex-linked recessive disease. Pedigree practice
What is the phenotype?
Male with hemophilia
What is the genotype?
XnY

17. Hemophilia – Sex-linked recessive disease. Pedigree practice
What is the phenotype?
Normal male
What is the genotype?
XNY

18. Hemophilia – Sex-linked recessive disease. Pedigree practice
What is the phenotype?
female with hemophilia
What is the genotype?
Xn Xn

19. Hemophilia – Sex-linked recessive disease. Pedigree practice
What is the phenotype?
Normal female
List all the possible genotypes.
XN Xn
XN XN
If you aren’t sure, put XN X?

20. Fill out the pedigree

23. Hemophilia – Sex-linked recessive disease. Summary
= XnY
= XnXn
= XNY
= XNXN Or XNXn Or XNX? 1. 2. 3. 4.