1. Read This on Monday:

What are Sex Linked Traits?

Biological sex in humans is determined by the X and Y sex chromosomes. Human females have two "X" chromosomes while human males have an "X" and a "Y" chromosome. Females receive one X from their mother and the other X from their father. Males receive one X from their mother and a Y from their father. Sex linked traits, make inheritance patterns different from what you've done so far..

If a recessive trait is located on the X chromosome, females must receive two recessive alleles for that trait to be expressed. For males, they only need one copy of the allele because there is no matching allele for that trait on their Y chromosome.

2. Watch This Video on Monday:

The following Amoeba Sisters' video gives a simple explanation with Punnet squares included.

3. Read This Example on Tuesday:

How To Solve Sex Linked Genetics Problems:

Example: In humans, hemophilia is a sex-linked recessive trait. If a female who is a carrier for hemophilia has children with a male with normal blood clotting:

a. What fraction of the female children will have hemophilia? Be carriers of the trait?

b. What fraction of the male children will have normal blood clotting? Have hemophilia, Be carriers?

Step 1 - Write the legend

Phenotype	Genotype
Normal Female	X^HX^H or X^HX^h
Female with hemophilia	X^hX^h
Normal Male	X^HY
Male with hemophilia	X^hY

Step 2 - Determine the parents' genotypes

Normal Female (carrier)	X^HX^h
Normal Male	X^HY

Step 3 - Create the Punnet Square

	X^H	X^h
X^H	X^HX^H	X^HX^h
Y	X^HY	X^hY

Step 4 - Carefully read and answer the questions

a. What fraction of the female children will have hemophilia? Be carriers of the trait?

None of the female children will have hemophilia
There is a 50% probability that the female child will carry the gene for hemophilia

b. What fraction of the male children will have normal blood clotting? Have hemophilia, Be carriers?

There is a 50% probability that the male child will have normal blood clotting
There is a 50% probability that the male child will have hemophilia
None of the male children will be carriers

4A. Do this worksheet on Wednesday. (Log into the chart room if you have a question)

Sex Linkage Worksheet- Version A.pdf

4B. Check your answers here on Wednesday

Sex Linkage Worksheet Answers - Version A.docx.pdf

5. Take the Sex Linkage Quiz in Schoology by Thursday's Class Meeting

6. Complete the Self Reflection in Schoology by Friday at 5 pm

7. Watch this Video (if or when you are bored or interested)

The Royal Family Story and Sex Linked Traits

( back to FrontPage)

Sex Linked Traits and Practice