LIFE SCIENCES GENETICS CROSSES

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?