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