Thursday 2/2

1. How many copies of the chromosome for skin color do you have? Why do you have that many?

2. 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?

• 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– MUCH more common in males

• Males have only 1 X– So if they have a recessive, it “shows”

• 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”

• 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