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Multiple Alleles• 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
Eye Color in Drosophila
• 4 alleles control eye color
• E1 = Wild
• E2 = Apricot
• E3 = Honey
• E4 = White
•E1 > E2 > E3 > E4
Normal Fruit Fly
Mutant Fruit Flies
Short winged fly
Curly winged fly
Normal fruit fly
Eye Color in Drosophila
• Phenotypes Genotypes• Wild Type E1E1, E1E2, E1E3,
E1E4
• Apricot E2E2, E2E3, E2E4
• Honey E3E3, E3E4
• White E4E4
Predict the phenotypic outcome if a honey coloredheterozygous fly is crossed with a white fly!
Phenotypes2 Honey : 2 White
Genotypes2 E3E4 : 2 E4E4
E3 E4
E4
E4
E3E4 E4E4
E3E4 E4E4
What are the possible phenotypes of the parents ina cross which produces the following offspring?
PhenotypesWild & Apricot
GenotpesE1E3 : E2E3
? ?
?
?
E1E2 E1E3
E2E3 E3E3
Possible alleles
C cch
ch
c
Another Example of Multiple Alleles
Antigen type Determines Blood type
Blood Types
A
AAA
A AA
AA
A
Person with blood type AHas antigen
A on RBC’s
&Antibody B
(floating in plasma)
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
Antigens A, B or Rh may be present on RBC surface
Blood Components
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
Predict the phenotypic outcome if a person with blood type AB mates with a person with type O!
Phenotypes1 Type A : 1 Type B
Genotypes2 IAi : 2 IBi
IA IB
i
i
IAi IBi
IAi IBi
Blood Typing Problem 1
MomBlood Type A
BabyBlood Type B
DadUnknown
Blood Type
IAIA orIA i
IBIB or IBi
Must carry
IB__IBIB
IBiIAIB
Blood Typing Problem 1
MomBlood Type B
BabyBlood Type O
DadUnknown
Blood Type
IBIB orIB i
ii
Must carry
i__IBiIAiii
Punnet Squares for Codominance
Calculate the probability of producing a son whois blood type A from the following cross!
Probability of producing a son
= 0.5
Prob. Ofproducing Type A
= 0.5
IA IB
i
i
IAi IBi
IAi IBi
Answer0.5 X 0.5 =
0.25 or25%
MustUse
Product Rule
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
• 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) = 0.125 or 1/8 or 13%• Diploma questions ask for answer
rounded to 2 decimal places or to 2 significant digits
Genetics Problem Set
www.biology.arizona
The Product Rule
Incomplete Dominance
Intermediate InheritanceSnapdragons
Red X White = Pink!!
Blending occurs
CodominanceCattle
Red X White = Roan
Both genes expressed
White and red hair present
Red X White = Pink
Gene for red (R) is incompletely dominant to gene for white (W)
Incomplete Dominance: Blending/3 distinct phenotypes
Predict the phenotypic outcome if a Red (RR)snapdragon is crossed with a White (WW) sd!
PhenotypesAll pink!
GenotypesAll RW
R R
W
W
RW RW
RW RW
Capital Lettersused for
both allelessince
they are equally Dominant
Predict the phenotypic outcome if a red (RR)snapdragon is crossed with a pink (RW) sd!
Phenotypes2 Red : 2 pink
Genotypes2 RR : 2 RW
R R
R
W
RR RR
RW RW
Intermediate?Or
Co-dominant?
Askyourself
doesblendingoccur??
Predict the genotypes of the parents!
Rr & Rr