1. Sex-Linked Genes Ms. Klinkhachorn March 21, 2011 Biology

2. DNA – March 21, 2011 The next day another couple walks into your office. You test both of their genes and you find that they are both carriers for Cystic Fibrosis. They tell you that they do not want to have a baby unless there is a 50% chance that their child will be healthy. Show the cross for this couple in the space below. 1.Describe this disease. 2.Is this a dominant or recessive disease? 3.Based on what the parents have told you, do you advise them to have a baby? Why/Why not? Give specific probabilities in your answer.

3. Objective SWBAT… – Understand sex-linked traits and complete Punnett Squares using this information

4. The Chromosomal Basis of Sex Two types of sex chromosomes – X and Y – Y is a lot smaller XX is female, XY is male – Females only pass on an x, but males can pass on an x or a y chromosome Your dad determines your sex

6. Sex-linked Genes Genes located on sex chromosomes are called sex-linked genes – Specifically on the X chromosome (the y doesn’t have many genes on it) Mom can pass on sex-linked alleles to boys and girls Dad can only pass on sex-linked alleles to girls

7. How would you set up a Punnett Square for a sex-linked trait?

8. Name the following genotypes: 1.X B X b = heterozygous dominant female 2.X B X B 3.X b X b 4.X B Y 5.X b Y

9. How is this different from what we did before?

10. Males cannot be carriers – they either have it or not – X R Y, X r Y Males have these kinds of traits more frequently – Have only one X, whereas girls have two – Girls have two copies of the gene, but males have one

11. Examples of Sex-Linked Traits Red-Green Colorblindness – Most common genetic disorder

12. Practice Problem: Colorblindness A man without colorblindness has children with a woman who is homozygous recessive for colorblindness. – Give the phenotype and genotype of each parent – Show the cross – What can we predict about any girls they will have? – What can we predict about any boys they will have?

13. Examples of Sex-Linked Traits Duchenne Muscular Dystrophy – Progressive weakening of the muscle and loss of coordination – Usually causes death in the 20s

15. Practice Problem A woman with muscular dystrophy has children with a man without muscular dystrophy. – Show the cross – Give the phenotype and genotype of each parent – If they have 4 children, what can we predict those children will be like (phenotype and gender-wise)

16. Examples of Sex-Linked Traits Hemophilia – Don’t have a gene necessary to make a protein responsible for blood clotting

17. DNA – March 22, 2011 You are a genetic counselor. A couple walks in to your office one day, and you notice that the wife has 6 fingers on her hand, but the husband has the normal number. The wife is homozygous dominant. – Show the cross – State the genotype and phenotype of the mom and dad – Give the phenotypic and genotypic ratio

18. Objective SWBAT… – Understand sex-linked traits and complete Punnett Squares using this information

19. Practice Problem: Hemophilia A woman is a carrier for hemophilia and her husband has the disease. Show the cross for this couple, state their phenotypes and genotypes, and give the genotypic and phenotypic ratio for their offspring.

20. Practice Problem Fruit flies have a sex-linked gene for eye color where red (R) is dominant over white (r). 1._X R X R ________ has the phenotype Red eyes 2._________ has the phenotype 3._________ has the phenotype 4._________ has the phenotype 5._________ has the phenotype

21. Practice Problem Baldness is also a sex-linked trait found on the X chromosome. To become bald, a person must have a recessive copy of the gene (b) on every X chromosome. Predict the genotypic and phenotypic ratios of the offspring if a woman who has no history of baldness in her family (B) had a baby with a man who was bald.

22. Write the genotype and phenotype for the following 1.Homozygous Recessive for colorblindness 2.Heterozygous for hemophilia 3.Dominant male for Muscular Dystrophy 4.Carrier for Cystic Fibrosis 5.Sick with Sickle-Cell 6.Male sick with colorblindness

23. Fill in the following table. Name of Disorder Dominant/R ecessive? Autosomal/ Sex-Linked? DescriptionSick Genotypes Healthy Genotypes