1. Investigating different patterns of inheritance
Codominance and Incomplete Dominance

2. Simple Mendelian Genetics

3. Codominance Both alleles of a gene pair are equally dominant.
Neither allele is dominant or recessive to the other and as a result both alleles are expressed in a heterozygous offspring.

4. Codominance
The heterozygous offspring will express (show) both phenotypes

5. Punnett Square for CodominanceX RR WW RW R R W RW RW
100% mixed color carnations (RW) RW RW W

6. Punnett Square for CodominanceX RW RW R W RR RW R
25% red carnations (RR)
50% mixed color carnations (RW)
25% white carnations (WW) RW WW W

7. Incomplete Dominance
One allele of a gene pair is only partially dominant over the other.
In these cases an intermediate form of the trait is expressed in heterozygous organisms.
Often seen in flowers.

8. Incomplete Dominance
The heterozygous offspring will express (show) a blend of the
Parent phenotypes

9. Punnett Square for incomplete dominanceX RR rr Rr R R
100% pink snapdragons (Rr) r Rr Rr Rr Rr r

10. Punnett Square for incomplete dominanceX Rr Rr R r R RR Rr
25% red snapdragons (RR)
50% pink snapdragons (Rr)
25% white snapdragons (rr) Rr rr r

11. Investigating different patterns of inheritance
Sex Linked Traits

12. Sex Linked Traits
Traits that are controlled by genes located on the sex chromosomes (X or Y)
These traits are more common in males than females.
Why???

13. Sex Linked Traits Girls = XX Boys = XY X Chromosome
Larger and contains multiple genes
Y Chromosome
Smaller and contains no genes
Girls = XX
Boys = XY

14. Sex Linked Traits XB XB - Normal XB YØ - Normal
Girls = XX Boys = XY
Color blindness is a recessive condition inherited on the X chromosome:
BB = Individual has normal vision
Bb = Individual has normal vision (carries the colorblind gene)
bb = Individual is colorblind
XB XB - Normal
XB YØ - Normal
XB Xb – Normal (carrier)
Xb YØ – Color Blind
Xb Xb – Color Blind

15. Are you colorblind?

16. Sex Linked Example Girls = XX Boys = XY Xb Xb XBXb XBXb XB XbYØ XbYØ
Consider a case where a mother is color blind and the father has normal vision. What is the probability that this couple’s children will be colorblind? Xb Xb
All Daughters are carriers (XBXb ) with normal vision
All Sons are color blind (XbYØ)
XBXb
XBXb XB
XbYØ
XbYØ YØ

17. Sex Linked Example Girls = XX Boys = XY XB Xb XBXB XBXb XB XBYØ XbYØ
Consider a case where a mother is a carrier and the father has normal vision. What is the probability that this couple’s children will be colorblind? XB Xb
50% the daughters will be carriers (XBXb ) but all will have normal vision.
50% of the sons will be color blind (XbYØ) and 50% will have normal vision (XBYØ).
XBXB
XBXb XB
XBYØ
XbYØ YØ

18. Sex Linked Traits are more common in boys
Girls = XX Boys = XY
What is the only way that a female can inherit colorblindness? XB Xb
XBXb
XbXb Xb
Dad has to be color blind and Mom has to at least be a carrier of the trait!
XBYØ
XbYØ YØ

19. Investigating different patterns of inheritance
Multiple Alleles

20. Multiple Alleles Traits that are controlled by three or more alleles.
Even though more that two alleles exist for a particular trait, humans only carry two at a time.
ABO Blood Type is a good example!

21. Blood Type - ABO Three alleles exist in the general population – A-B-O
Humans only carry two
A and B are co-dominant
O is recessive
Let’s see how this works!

22. Blood Type - ABO A and B are Co-Dominant and O is recessive
What allele combinations are possible for A blood type?
AA or AO
What allele combinations are possible for B blood type?
BB or BO

23. Blood Type - ABO A and B are Co-Dominant and O is recessive
What allele combination is possible for AB blood type? AB
What allele combination is possible for O blood type? OO

24. A O A O AO OO O AO OO O ABO Blood Type
Consider the following genotypes:
Father genotype = AO Father’s Blood Type = ________
Mother Genotype = OO Mother’s Blood Type = ________ A O A O
What are the possible blood types for the children? What are the genotypes?
50% chance of blood type A (AO)
50% chance of blood type O (OO) AO OO O AO OO O

25. B O BO OO O BO OO O ABO Blood Type
Consider a family where the father is blood type B, the Mother is blood type O, and their daughter is blood type O. What is the possibility that future children will have the following blood types?
Why not BB? B O
Blood type A _____%
Blood type B _____%
Blood type O _____%
Blood type AB _____% BO OO O 50 50 BO OO O

26. Most Common Blood types in the United States