Topic 3: Sex-Linked Inheritance and Gender Determination

Topic 3: Sex-Linked Inheritance and Gender Determination
Due Thursday, May 20th

This session we will explore inheritance patterns associated with genes located on the sex chromosomes. We will also look at the role that sex chromosomes play in sex determination and gender.

Assignment 1: Battle of the Sexes

Genes physically located on the sex chromosomes are called sex-linked genes. Genes found on the X chromosome are X-linked, while genes on the Y chromosome are Y-linked. Only males inherit Y-linked genes, since females do not have a Y chromosome. Males inherit their Y chromosomes from their fathers.

Males inherit one X chromosome from their mother, and are called "hemizygous" for a given X-linked trait. Females inherit two X chromosomes (one from mom, one from dad) and can be either homozygous or heterozygous for a given X-linked trait.
Examples of X-linked recessive disorders include muscular dystrophy, hemophilia, and red-green colorblindness.

A male who inherits a recessive disorder allele on his X chromosome will exhibit that disorder, since he does not have a second X chromosome (containing a normal allele) to mask the disorder allele. As a result, there are no male carriers for X-linked disorders. On the other hand, females can be carriers for X-linked recessive disorders since they inherit two X chromosomes (and the second X chromosome might contain the normal allele).

For this assignment, we will explore X-linked recessive inheritance patterns.

To begin:

Read:

Text pages 358-364.

Part A: Sample Problems to Try:

1) Colorblindness is an X-linked recessive trait. If a colorblind male and a homozygous normal female have children, will any of the children be colorblind? Show the Punnett square.

2) Colorblindness is an X-linked recessive trait. If a normal male and a colorblind female have children, will any of the children be colorblind? Show the Punnett square.

Sites to Visit:


Part B: Sex-Linked Inheritance Tutorials and Practice Problems
http://www.biology.arizona.edu/mendelian_genetics/problem_sets/sex_linked_inheritance/sex_linked_inheritance.html

WRITE DOWN THE ANSWERS TO QUESTIONS 1-10 AND TURN THEM INTO MS. JOHNSON ON THURSDAY, MAY 20TH!!!


Part C: Complete the worksheet you were given in class, "Sex Linked Inheritance"


So...due Thursday, May 20th

-Part A: 2 simple sample problems
-Part B: Answers to online tutorial practice questions 1-10
-Part C: Sex-linked Inheritance worksheet you received in class.