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

• Male

• Female

Connecting Pedigree Symbols

• Fraternal twins

• Identical twins

Examples of connected symbols:

Connecting Pedigree Symbols

• Married Couple

• Siblings

Examples of connected symbols:

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? __________________________