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

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

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

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

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

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?

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

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?

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

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

Albinism not just in people

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

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”

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”

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

Cystic Fibrosis: http://www.youtube.com/watch?v=Dn0grhu9h4g Achondroplasia: http://www.youtube.com/watch?v=Bn7eGRsYYGI Huntington’s: http://www.youtube.com/watch?v=uVkzi-kdOrc Albinism: http://www.youtube.com/watch?v=OrX5HflxQQs Hemophilia: http://www.youtube.com/watch?v=X9Qrm6o4tNQ