Sex-linked traits are caused by genes located on the X or Y chromosomes, with X-linked traits more common. Males typically only have one copy of the X chromosome and are thus more likely to exhibit sex-linked traits. Females have two X chromosomes and one trait can be compensated for by the other chromosome through X-inactivation.

1. Phenotypic Expression Varies
• Complete Dominance
• Codominance
• Incomplete Dominance
• Sex-Linked
 X-linked: gene lies on X
chromosome (males only
have one copy of the gene)
 Y-linked: gene lies on Y
chromosome (only males
have the gene)
 Contributes to younger Hemophilia
mortality rate in males
• Polygenic Traits

2. Phenotypic Expression Varies
• Complete Dominance
• Codominance
• Incomplete Dominance
• Sex-Linked
 X-linked: gene lies on X
chromosome (males only
have one copy of the gene)
 Y-linked: gene lies on Y
chromosome (only males
have the gene)
 Contributes to younger
mortality rate in males
• Polygenic Traits Hemophilia

3. Phenotypic Expression Varies
• Complete Dominance
• Codominance
• Incomplete Dominance
• Sex-Linked
 X-inactivation disables one x-
chromosome in each cell
(females and males each
only use one x-chromosome)
 can lead to unique
phenotypes in females
• Polygenic Traits

4. Practice
• Sex-linked practice “Pipe Cleaner
babies and genetic traits”. Complete
and glue to page ___ of your notebook
• OR, do sex linked handout

5. X Linked Genetics in the Calico Cat
Calico is a coat color found in cats, which is caused by
a SEX-LINKED, CODOMINANT allele.
B = black, R = orange, and BR = calico.
The following genotypes are possible;
Female cats can be black XBXB, orange XRXR, or
calico XBXR
Male cats can be black XBY or orange XRY

6. Phenotypic Expression Varies
• Complete Dominance
• Codominance
• Incomplete Dominance
• Sex-Linked
• Polygenic Traits
 Controlled by more than
one gene
 Most common type of
expression

7. Pedigree Rules
• What is a pedigree?
• *A pedigree is a chart that shows all
family members and how they are
related. It follows certain rules and
shows genotypes and phenotypes.

8. – Boys Shaded-
Phenotype being
“traced”
– Girls X deceased
Marriage same level=same
generation
Mating w/o marriage Carrier
(heterozygous)
Kids Adopted

9. • Draw a pedigree for your immediate
family (mom, dad, step parents,
siblings, etc)

11. Trait

12. Trait

13. Trait
traits

14. Trait
traits

15. Trait

16. Trait

18. Pedigrees
• Graphically shows the
lineage of a disorder in
a particular family
• Be able to tell if
disorder is
dominant, recessive, or
sex-linked from a
pedigree
• Be able to predict the
chance that an
indicated couple will
have a child with the
disorder

19. Pedigrees
• Autosomal: Not sex-linked
Where would a gene
be if it was
Human Chromosomes
autosomal?
Where would it be if it
was sex-linked?
What gender is this
person?

20. Pedigrees
• Autosomal: Not sex-linked
Autosomal Dominant
How can we tell?
Human Chromosomes

21. Pedigrees
Autosomal Recessive
How can we tell?

22. Pedigrees
Sex-Linked
How can we tell?
Is the X-linked dominant or recessive?

23. Pedigree Analysis Case Study
• Read family information
• Put family name at the top of your whiteboard
• Make a pedigree for the entire family
• Label names of all family members that you know
• Make a key for the possible genotypes and phenotypes of your trait. Label as
many individual genotypes on the pedigree that you can.
• Shade in the people that have the trait
• Identify the Patterns in the Pedigree and write the following answers on your
whiteboard:
– Is the trait dominant or recessive?
– Does the trait show up in every generation? Or, does the trait skip a
generation?
– Does the trait affect males/females equally? Or, Does the trait only affect
males? Or, only females?
– Does your trait fit our model? (why or why not?) If not, what rule(s) need to
change, or what new rules do you need to explain how this trait is inherited?
• YOUR PATTERN SHOULD SUPPORT YOUR ANSWER.
•