Patterns of Inheritance

• All of the traits and problems that we have talked about so far have been traits that are controlled by Dominant and Recessive Alleles.

• This is not the only type of inheritance pattern that exists however

• Today we will talk about Co-Dominant Alleles

Co-Dominance

• Co-Dominant Alleles: these are pairs of alleles which BOTH affect the phenotype of an organism when present in the heterozygous state

• For example:• X

P: Red Flower (RR) White Flower (rr) Pink Flower (Rr)

What Would You Expect the Genotype/Phenotype Ratios to be in the F2 Generation?

X ?

F1: Pink Flower Pink Flower (Rr) (Rr)

There is an important example of Co-Dominant Alleles in Humans

• BLOOD TYPES!!!!!

• Does anyone know what their blood type is?

One gene determines the ABO blood type of a person. There are three different alleles that can be found at the locus for blood type. These are…

Blood Type Alleles

IA – Type A AlleleIB – Type B Allelei – Type O Allele

Both the IA and IB alleles are dominant over the i alleleIA and IB are co-dominant to one another

Blood Genotypes and Phenotypes

Due to the nature of these alleles, four phenotypes are possible:Type A, Type B, Type AB, and Type O

Alleles IA IB iIA IAIA IAIB IAiIB IAIB IBIB IBii IAi IBi ii

These Blood Type Differences are Very Important!

• Our immune system is designed to identify foreign material in our body and to try and remove it

• Each of the cells of our body have proteins on their membrane called antigens which the immune system can use to identify the cells as native

• Depending on a persons blood type, the red blood cells produce different antigens on their membranes

Antigens

• Type A blood cells have Type A Antigens• Type B blood cells have Type B Antigens• Type AB blood cells have both the Type

A and Type B Antigens on their cell membrane• Type O blood cells have no antigens on

their cell membrane

Blood Transfusions

• Because of our immune system, our bodies can only accept blood that contain antigens that our bodies recognize as native• E.g. People with Type B blood cannot accept blood which has Type A

antigens on its cells

People with Type ____ blood are known as Universal Acceptors because they can accept any type of blood

People with Type ___ blood are known as Universal Donors because their blood can be accepted by people of any blood type

Possible Test Questions

• There is a practical joker in the maternity ward who removed all the baby id bracelets. There are three babies that cannot be easily distinguished and the parents want to be sure they get the right ones back so the doctors do a blood test. A particular mom is homozygous type A and the dad is type O. The babies have blood types AB, A, and O. Show your work and indicate which baby must be theirs

Possible Test Questions

• The police have rounded up the usual suspects in the latest rash of bookstore robberies. The thief got a nasty paper cut at the scene of the crime. The suspects are of blood types O, A, B and AB. The blood at the crime scene contained i alleles. Which suspect therefore cannot have been involved? Explain

More Practice Questions

• A man with AB blood is married to a woman with AB blood. What blood types will their children be and in what proportion?

• A man with Type A blood is married to a woman with Type O blood and wants to find out what his genotype is. He and his wife have 8 children together. How might he determine his genotype without having tests done?