Journal Entry Why are sex-linked recessive traits such as red-green colour-blindness and hemophilia more commonly found in males than in females? Explain your answer in terms of the X chromosome. http://www.khanacademy.org/video/sex-linked-traits?topic=biology

Pedigrees A table to explain how sex-linked traits are passed along

Constructing a Pedigree Female Male

Connecting Pedigree Symbols Examples of connected symbols: Fraternal twins Identical twins

Connecting Pedigree Symbols Examples of connected symbols: Married Couple Siblings

Pedigree uses: autosomal dominant conditions (e.g.Huntington disease, polydactyly) autosomal recessive conditions (e.g., cystic fibrosis, Tay-Sachs disease, attached earlobes) sex-linked recessive conditions (e.g., colour-blindness, Duchenne muscular dystrophy, hemophilia)

What they tell us Pedigrees will display phenotypes and gender Genotypes can only be determined using logic! http://www.zerobio.com/drag_gr11/pedigree/pedigree_overview.htm

Problem 1

Problem 2

1. How many generations are represented in the chart for sickle-cell anemia? __________ 2. How many carriers of the sickle-cell trait are in each generation? _________________ 3. How many people in the family were born with sickle-cell anemia? _______________ 4. From with parent did the second-generation children inherit the sickle-cell gene? ____ 5. In which generation did sickle-cell anemia first show? __________________________