This document discusses several genetic concepts including incomplete dominance, codominance, sex-linked traits, polygenic traits, and multiple alleles. It provides examples for each concept. Incomplete dominance is when neither allele is fully dominant, resulting in an intermediate phenotype in heterozygotes. Codominance is when both alleles are expressed simultaneously in the heterozygote. Sex-linked traits are located on sex chromosomes, most often the X chromosome, resulting in different inheritance patterns between males and females. Polygenic traits are influenced by multiple genes, resulting in a range of possible phenotypes. Multiple alleles refers to traits with more than two possible alleles, such as blood types.

1. Genetic Crosses

2. Incomplete Dominance
• One allele for a trait is not dominant
over the other
• Heterozygous condition produces a
phenotype that is intermediate of the
two alleles
• Use capital form of two different letters

3. Incomplete Dominance
Red Snaps White Snaps
RR
WW
RW
All Pink
RW X RW

4. Codominance
• One allele for a trait is not dominant
over the other
• The heterozygous condition
produces a phenotype in which both
variations appear

5. Codominance

6. Try these two
1) In cats when a long tailed cat is bred with a no
tailed cats short tailed cats are produced. If a
short tailed cat was bred with a no tailed cat,
what is the likelihood that a short tailed cat would
be produced? Is this incomplete or
codominance?
2) Also in cats a black haired cat and a white haired
cat produce a tuxedo (mix of black and white). If
a two tuxedo cats were bred, what would be the
likelihood of producing a white cat? Is this
incomplete or codominance.

7. Sex-Linked Traits Activity
Hemophiliac
Male
Xh
Y
Normal MaleXH
Y
Hemophiliac
Female
Xh
Xh
Carrier FemaleXH
Xh
Normal FemaleXH
XH
Overall
Total
Group TotalPhenotypeGenotype

8. Sex Linked Traits
• Traits that have a gene (allele) located
on a sex-chromosome. Most traits the
gene is located on the X chromosome
• Since males have only one of two X
chromosomes they only need one
recessive gene to carry the trait.
• Must include sex chromosome in cross
• Examples are colorblindness and
hemophilia

9. Colorblindness Test

10. Sex-linked Trait example
• Normal vision is dominant to
colorblindness. A heterozygous
(carrier) female marries a normal male.

11. 3-2-1 Think about
• List 3 human traits that seem to have a
range of possible variations (rather than
simply 2 or even 3 distinct variations)
• Describe 2 reasons why you think traits
could have a range of variations
• Give one definition for the word
POLYGENIC

12. Polygenic Traits
• Traits controlled by more than one
gene.
• Usually creates a range of variations
possible
• Examples: Eye color, skin color, hair
color, height
• See Child/Grandchild lab for examples

13. Answer the following
• How similar or different does your child
look compared to you in terms of hair,
eye, or skin color?
• How could the genotypes of the child
change to make them look more/less
similar than you?

14. Multiple Alleles
• More than two alleles (gene variations)
for a trait.
• Example A B O blood types

15. Blood Type
Donate
/Receive
iiO
IA
IB
AB
IB
IB
IB
iB
IA
IA
IA
iA
Antibody
for:
Antigen
on Blood
GenotypeBlood
Type

16. Blood Type Examples
• A woman with O blood and man with A blood
marry. Could they have a child with O blood?
Could it be possible that there is no chance of
having children with O blood?
• A man with B blood marries a woman with AB
blood. They have a child with A blood. What
has to be dads genotype? Prove it.
• A man with A blood (IA
IA
) and woman with B
blood (IB
IB
) have a child. The child needs a
blood transfusion. Do they need to worry
about the child getting the wrong type of
blood? Why or why not?