Multiple Alleles

Genetics UnitBiology 30

Mrs. S. Pipke-Painchaud

Multiple Alleles

• have 3 or more alleles for the same gene (or at a single locus) 

• In Other Words – there are 3 or more alleles that create the different traits. 

• at most one individual will have 2 alleles or 1 pair  (unit factors exist in pairs.) 

• in a species, however, many alternative forms exist 

Example – ABO Blood Group

• this deals with the presence of antigens– These are like labels/ name tags on the blood

cells.

• Each individual has 1 of 4 phenotypes – Type A– Type B– Type AB– Type O

– What are you?

http://www.rrsd.mb.ca/ResourcesandProjects/grade8/images/red%20blood%20cells.jpg

The Info You Need To Know• Gene designated is I (isoagglutinogen)

– I  = A antigen – I  = B antigen– i  = no antigen 

• IA and IB are both codominant 

• IA and IB are both dominant to I (type O)

Genotype Antigen Phenotype 

IAIA A A

IAi A A

IBIB B B

IBi B B

IAIB AB AB

i i Neither O

• http://learn.genetics.utah.edu/units/basics/blood/types.cfm

Website Resoures• Nobel Prize – Blood Typing Website:

– http://nobelprize.org/educational_games/medicine/landsteiner/readmore.html

– View for animations and background info on blood types.

• Wikipedia – Blood Types– http://en.wikipedia.org/wiki/Blood_type– Contains a chart of blood types by nation.

• Maps of the Distribution of Human Blood Types all over the World.– http://anthro.palomar.edu/vary/vary_3.htm

• Sickle Cell Anemia Example:– http://www.astrographics.com/GalleryPrintsIndex/GP2146.html

Did You Know?• B is the rarest allele. • 16% of the population have it.

– Distribution of Blood Types • http://anthro.palomar.edu/vary/vary_3.htm

http://www.faqs.org/health/images/uchr_01_img0015.jpg

http://www.uwosh.edu/med_tech/teaching/ElementaryHemeWeb/LEARN%20ABOUT%20RBCS%20AND%20PLTS.htm

• Wikipedia: http://en.wikipedia.org/wiki/Image:ABO_blood_type.svg

Practice

• If a person with Type A (Heterozygous) blood married and had children with a person who has Type B (Heterozygous) blood, what would the genotypic and phenotypic ratios be?– IAi X IBi

IA i

IB IAIB IBi

i IAi ii

Genotypic Ratio:

1 IAIB : 1 IAi: 1 IBi: 1 ii

Phenotypic Ratio:

1 AB: 1 A: 1 B: 1 O

Practice

• If you crossed a person with type 0 with heterozygous type B, what would the phenotypic ratio be?– ii X IBi – Phenotypic Ratio:

• 1 B : 1 O

i i

IB IBi IBi

i ii ii

Website Resoures• Nobel Prize – Blood Typing Website:

– http://nobelprize.org/educational_games/medicine/landsteiner/readmore.html

– View for animations and background info on blood types.