1. Complex Patterns of Inheritance
Exceptions to Mendel’s rules:
not simple dominant/recessive inheritance

2. The phenotype of the heterozygote is INTERMEDIATE.
Incomplete Dominance
The phenotype of the heterozygote is INTERMEDIATE.
Red + White = Pink

3. Red parent plant R R
RR’ R’
White parent plant R’
All pink offspring!

4. Both alleles are expressed!
Codominance
Both alleles are expressed!
Cross a Brown and
White Cow!
B=Brown W=White
BW=Brown and White

5. Multiple Alleles
When a gene has more than 2 forms of an allele (conflicts with Mendel’s 2nd conclusion); There are more than just one dominant and one recessive allele
Blood Types: A, B, AB, O
A and B are codominant
O is recessive to both

6. Type A: IAIA or IAi Type B: IBIB or IBi
Type AB: IAIB Type O: ii

8. Pretend that Brad Pitt is heterozygous for the type B allele and Angelina Jolie is Type O. If they have a child, what are all the possible blood types of their baby? What if he is homozygous for type B?

9. Polygenic Traits
Trait controlled by two or more GENES (not alleles) OR interaction with the environment
AaBbCc x AaBbCc
Skin Pigmentation
Gene to make melanin
Gene to bring nutrients to melanin-producing cells (melanocytes)
Gene to turn on/off melanin when in continued presence of UV light
Traits vary along a bell curve

10. Sex-Linked Traits Traits that affect genes on the X chromosome
Females: XX Males: XY
There are X-linked dominant and X-linked recessive traits
Males only have to inherit one version for it to show
Females can have a copy of the affected allele on 1 X chromosome and NOT have the disorder
Examples of X-linked Dominant Disorders: Vitamin D Rickets
Examples of X-linked Recessive Disorders: Male-Pattern Baldness, Color Blindness, Hemophilia
Baldness

11. Vitamin D Rickets Vitamin D allows calcium to be absorbed.
No calcium absorption = weak, flimsy bones

12. Punnett Squares for the sex-linked trait hemophilia
Cross a heterozygous (carrier) female for hemophilia with a normal male:
XNXn x XNY
N = Normal
n = hemophilia