1. Thursday 2/2
How many copies of the chromosome for skin color do you have? Why do you have that many?
What is similar and what is different about the chromosomes you have that determine skin color
Agenda
1. Finish Karyotype Activity
2. Discuss single gene disorders

2. Single Gene Disorders Inherited from parents like other traits
May be recessive or dominant

3. Ex: Cystic Fibrosis
Lungs make too much mucus
cc = Cystic Fibrosis
CC or Cc = no disease

4. Carrier Has a “hidden” recessive allele for disease Ex: Cc
has no disease, but can pass on disease allele
1/25 Caucasians are carriers
Genetic testing on one
parent only
If both parents carriers
what are odds of
having a child affected

5. Ex: Achondroplasia (dwarfism)
Growth factor imbalance
Aa = dwarf
aa= average height
AA = lethal (embryo cannot survive)

6. Two people heterozygous for dwarfism.
What are the odds of their children having dwarfism?
Odds of having a baby that does not survive to birth?

7. Muscles weaken progressively
Huntington’s Disease
Muscles weaken progressively
Begins about age 40
Hh = Huntington’s
hh = no disease
HH = lethal

8. Why would this get passed on if it is a dominant trait?
What is the chance of two people with Huntington’s having a normal baby?
What is the chance of two people who are homozygous for huntington’s having a baby?

9. Albinism Cells do not make melanin May have pink or blue eyes
aa = albino
AA or Aa = have melanin

10. If two normal skin parents give birth to an albino child, what is the genotype of the parents?

11. Albinism not just in people

12. Sex-Linked Traits Some genes are on X chromosome
But have no matching gene on Y

13. Recessive form of trait Males have only 1 X
MUCH more common in males
Males have only 1 X
So if they have a recessive, it “shows”

19. Gene for color vision is on X XCXC OR XCXC
Ex: Colorblindness
Gene for color vision is on X
C is normal, c is colorblind
XCXC OR XCXC
Females with normal color vision
XCY
Male with normal color vision
XCXC OR XCY
Female or male with colorblindness
Males have no “back up”
What is on their X “shows”

20. Gene for blood clotting is on X
Ex: Hemophilia
Gene for blood clotting is on X
Normal clotting is dominant
Hemophilia is recessive
People with only recessive have Hemophilia

21. Cystic Fibrosis:
Achondroplasia:
Huntington’s:
Albinism:
Hemophilia: