1. Notes Pg. #16: Complex Genetics
EQ: Are there other, more complicated, types of inheritance?

2. Incomplete Dominance
Incomplete Dominance - Situation in which one allele is not completely dominant over another- phenotypes mix/blend.
Example When straight hair and curly hair are crossed, wavy hair results.
Alleles:
S= Straight (dominant)
S’= Curly (recessive)
Genotype=Phenotype:
SS =Straight hair
SS’=Wavy hair
S’S’=Curly hair

3. Incomplete dominance in Rats
If you crossed a white rat and a black rat using incomplete dominance what offspring would you get? +
Discuss with your neighbor!

4. Example incomplete dominance Punnett:
Red and white flowers are crossed and pink flowers are produced.
Genotype=Phenotype:
RR=Red
RR’=Pink
R’R’=White

5. You try: incomplete dominance
#1: Cross a curly-haired mother with a wavy-haired father, then summarize the genotype & phenotype percentages:
Genotype=Phenotype:
SS =Straight hair
SS’=Wavy hair
S’S’=Curly hair

6. Codominance
Codominance - Situation in which both alleles of a gene contribute equally to the phenotype of the organism.
Example – A solid white cow is crossed with a solid black cow and the resulting offspring are spotted black and white (spotted is also called roan).
Alleles: W=white, B=Black
Genotype = Phenotype:
WW=White cow, BB= Black cow, WB=White & Black spotted cow [NOT gray!] +

7. Example Codominance Punnett:
If you cross a red and white flower, you get a flower with red & white splotches.
Genotype = Phenotype:
RR=Red
WW=White
RW=Red & White spots
[NOT a mix-
NOT pink!]

8. Co-dominance in Rats Discuss with your neighbor!
If you crossed a white rat and a black rat using codominance what offspring would you get? +
Discuss with your neighbor!

9. You Try: codominance
#2: Cross a speckled “erminette” chicken with a white chicken. Summarize the genotype and phenotype results as percentages:

10. Label the pictures
When you cross a red & white flower, what do you get?
1. If red is dominant /with regular [complete] dominance?
2. With incomplete dominance?
3. With codominance?

11. Check yourself: Which type of inheritance is this?
Incomplete dominance
Incomplete dominance!

12. Check yourself: Which type of inheritance is this?
Incomplete
Incomplete dominance!

13. Check yourself: Which type of inheritance is this?
Codominance
Co-dominance!

14. Check yourself: Which type of inheritance is this?
Tall plant
Medium plant
Incomplete dominance
Short plant
Incomplete dominance!

15. Check yourself: Which type of inheritance is this?
Codominance
Codominance!

16. Check yourself: Which type of inheritance is this?
Codominance –both present in spots
Codominance!

17. Check yourself: Which type of inheritance is this?
Incomplete dominance- mixing of two patterns
Incomplete Dominance!

18. Multiple Alleles
Multiple Alleles- Three or more alleles of the same gene.
Even though three or more alleles exist for a particular trait, an individual can only have two alleles - one from the mother and one from the father.

19. Examples of Multiple Alleles
Coat color in rabbits is determined by a single gene that has at least four different alleles. Different combinations of alleles result in the fur colors you see here.

20. Examples of Multiple Alleles
Blood Type – 3 alleles exist (IA, IB, and i), which results in four different possible blood types
Hair Color – Too many alleles exist to count
There are over 20 different shades of hair color.

21. Multiple alleles: human Blood types
The 4 human blood types A, B, AB & O made from 3 alleles: lA, lB, & i
lA & lB are dominant to i
lA & lB are codominant

22. human Blood types 4 Human Blood Types: Genotypes A A lA lA or lAi
Surface Molecules
Phenotypes A A
lA lA or lAi
lB lB or lBi B B
lA lB
A and B AB ii
None O

23. Section 12.3 Summary – pages 323 - 329
Phenotype A
Surface molecule A
The lA allele is dominant to i, so inheriting either the lAi alleles or the lA lA alleles from both parents will give you type A blood.
Surface molecule A is produced.
Section 12.3 Summary – pages

24. Section 12.3 Summary – pages 323 - 329
Phenotype B
Surface molecule B
The lB allele is also dominant to i.
To have type B blood, you must inherit the lB allele from one parent and either another lB allele or the i allele from the other.
Surface molecule B is produced.
Section 12.3 Summary – pages

25. Section 12.3 Summary – pages 323 - 329
Phenotype AB
Surface molecule B
The lA and lB alleles are codominant.
This means that if you inherit the lA allele from one parent and the lB allele from the other, your red blood cells will produce both surface molecules and you will have type AB blood.
Surface molecule A
Section 12.3 Summary – pages

26. Section 12.3 Summary – pages 323 - 329
Phenotype O
The i allele is recessive and produces no surface molecules.
Therefore, if you are homozygous ii, your blood cells have no surface molecules and you have blood type O.
Section 12.3 Summary – pages

27. Example: Blood types
What are the genotype & phenotype chances for this offspring?

28. You try: Blood type Punnett
Cross a Mother who is heterozygous for blood type B, with a Father who has blood type AB:
What are the genotype and phenotype percentages?

29. Multiple Alleles There Are Always Multiple Alleles!
Genetic inheritance is often presented with straightforward examples involving only two alleles with clear-cut dominance. This makes inheritance patterns easy to see.
But very few traits actually only have two alleles with clear-cut dominance. As we learn more about genetics, we have found that there are often hundreds of alleles for any particular gene.
We probably know this already - as we look around at other people, we see infinite variation.

30. Polygenic Trait
Polygenic Trait - Trait controlled by two or more genes.
Polygenic traits often show a wide range of phenotypes.
Example: The wide range of skin color in humans comes about partly because more than four different genes probably control this one trait... No wonder DNA is soooo looooong!