1. Multiple Alleles Eye color in Drosophila (fruit flies)
For each trait observed by Mendel….
Only 2 alleles existed (T & t, for example)
Many traits are controlled by multiple alleles
2 examples include
Eye color in Drosophila (fruit flies)
Blood types in humans

2. Eye Color in Drosophila
4 alleles control eye color
E1 = Wild
E2 = Apricot
E3 = Honey
E4 = White
E1 > E2 > E3 > E4

3. Normal Fruit Fly

4. Mutant Fruit Flies
            
            
                  
Short winged fly
Normal fruit fly
Curly winged fly

5. Eye Color in Drosophila
Phenotypes Genotypes
Wild Type E1E1, E1E2, E1E3, E1E4
Apricot E2E2, E2E3, E2E4
Honey E3E3, E3E4
White E4E4

6. E3 E4 E4 E4 E3E4 E4E4 E3E4 E4E4 Phenotypes Genotypes 2 E3E4 : 2 E4E4
Predict the phenotypic outcome if a honey colored
heterozygous fly is crossed with a white fly! E3 E4 E4
E3E4
E4E4 E4
E3E4
E4E4
Phenotypes
2 Honey : 2 White
Genotypes
2 E3E4 : 2 E4E4

7. ? ? ? ? E1E2 E1E3 E2E3 E3E3 Genotpes E1E3 : E2E3 Phenotypes
What are the possible phenotypes of the parents in
a cross which produces the following offspring? ? ? ?
E1E2
E1E3 ?
E2E3
E3E3
Genotpes
E1E3 : E2E3
Phenotypes
Wild & Apricot

8. Another Example of Multiple Alleles
Possible
alleles C
cch ch c

9. Antigen type
Determines
Blood type
Blood
Types

10. Person with blood type A Has antigen A on RBC’s & Antibody B
(floating in plasma) A A A A A A A A A A

11. i is recessive to IA and IB
Blood Typing in Humans
Another example of multiple alleles
Controlled by 3 alleles
IA, IB and i
IA and IB are said to be codominant
If a person inherits both of them, then antigen A and antigen B are on the RBC’s
i is recessive to IA and IB

12. Blood Components
Antigens A, B or Rh
may be present
on RBC surface

13. Genotypes and Phenotypes for ABO Blood Types
Genotype Phenotype Blood Type
IAIA, IAi A antigen A
IBIB, IBi B antigen B
IAIB A & B antigen AB
ii neither antigen 0

14. IA IB i i IAi IBi IAi IBi Phenotypes Genotypes 2 IAi : 2 IBi
Predict the phenotypic outcome if a person with
blood type AB mates with a person with type O! IA IB i
IAi
IBi i
IAi
IBi
Phenotypes
1 Type A : 1 Type B
Genotypes
2 IAi : 2 IBi

15. Blood Typing Problem 1 IB__ IBIB or IBi Dad Mom Unknown Blood Type A
Must carry
IB__
IBIB
IBi
IAIB
IAIA or
IA i
Baby
Blood Type B
IBIB or IBi

16. Blood Typing Problem 1 i__ ii Dad Mom Unknown Blood Type B Blood Type
Must carry
i__
IBi
IAi ii
IBIB or
IB i
Baby
Blood Type O ii

17. Punnet Squares for Codominance

18. IA IB i i Must Use Product Rule IAi IBi IAi IBi Probability of
Calculate the probability of producing a son who
is blood type A from the following cross! IA IB
Must
Use
Product
Rule
Answer
0.5 X 0.5 =
0.25 or
25% i
IAi
IBi i
IAi
IBi
Probability of
producing a son
= 0.5
Prob. Of
producing Type A
= 0.5

19. Blood Typing and Gender
Calculate the probability of producing a daughter who is blood type A from a cross between a Type B mother and a Type A father, given that each of these individuals have a parent with Type O.
Since parents are ii, both must be carriers for i
Mother must be IBi, Father must be IAi

20. Prob. of producing Type A = 0.25
Prob. of producing a daughter = 0.50
Therefore prob of producing Type A daughter must be found with the product rule……..
0.25 ( 0.5) = or 1/8 or 13%
Diploma questions ask for answer rounded to 2 decimal places or to 2 significant digits

21. Genetics Problem Set

22. The Product Rule

23. Incomplete Dominance Codominance Intermediate Inheritance Cattle
Snapdragons
Red X White =
Pink!!
Blending occurs
Codominance
Cattle
Red X White = Roan
Both genes
expressed
White and red
hair present

24. Gene for red (R) is incompletely dominant
Red X White = Pink
Gene for red (R) is incompletely dominant
to gene for white (W)

25. Incomplete Dominance: Blending/3 distinct phenotypes

26. R R W W RW RW RW RW Phenotypes Genotypes All RW
Predict the phenotypic outcome if a Red (RR)
snapdragon is crossed with a White (WW) sd! R R
Capital Letters
used for
both alleles
since
they are equally
Dominant W RW RW W RW RW
Phenotypes
All pink!
Genotypes
All RW

27. R R R W RR RR RW RW Phenotypes Genotypes 2 RR : 2 RW
Predict the phenotypic outcome if a red (RR)
snapdragon is crossed with a pink (RW) sd! R R R RR RR W RW RW
Phenotypes
2 Red : 2 pink
Genotypes
2 RR : 2 RW

28. Intermediate? Or Co-dominant?
Ask
yourself
does
blending
occur??

29. Predict the
genotypes of
the parents!
Rr & Rr