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Powerpoint Presentation: Multiple Alleles

 

Genetics Index

Chromosomes
Meiosis
Meiosis: Crossing over
Mitosis and Meiosis
Introduction to Mendelian Genetics
Test Cross
Codominance
Pedigree Charts
Twin Studies
The dihybrid cross
Dihybrid Cross : Test Cross
Autosomal Linkage
The Genetic Diagram for Linked Genes
Calculating the cross over value using a test cross
Sex determination and sex linkage
Sex linkage
Genetic diagram for sex linked genes
Blood Clotting and Haemophilia
The Retina and Daltonism
Genetic Modification
Cloning Animals
Cloning Plants

Topic Chapters Index

 

Blood types and transfusions

Blood types vary and your immune system recognises your own blood type as being self. Other blood types are recognised as non-self.

If a blood which is incompatible with your body is transfused it will result in the agglutination of the foreign red blood cells. This could be harmful to the patient so it is essential that the blood types are determined before a transfusion.

People who are Type A blood produce antibodies to agglutinate cells which carry Type B antigens. They recognise them as non-self.

The opposite is true for people who are Type B.

Neither of these people will agglutinate blood cells which are Type O. Type O cells do not carry any antigens for the ABO system. Type O cells pass incognito.

The table below summarises the compatibilities between the blood types at transfusion.

blood groups

 

Note:

Type O blood may be transfused into all the other types. It is called the universal donor.

Type AB blood can receive blood from all the other blood types. It is called the universal recipient.

 

GENETICS

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Multiple Alleles

About 30% of the genes in humans are di-allelic, that is they exist in two forms.

About 70% are mono-allelic, they only exist in one form and they show no variation.

A very few are poly-allelic having more than two forms.

 

Poly-allelic genes

Poly-allelic genes are usually associated with tissue types. They are so varied that they provide us with our genetic finger print.

  • Di-allelic genes can generate 3 genotypes.

  • Genes with 3 alleles can generate 6 genotypes.

  • Genes with 4 alleles can generate 10 genotypes.

  • Genes with 8 alleles can generate 36 genotypes

This is very important to our immune system which must tell the difference between our own cells and invading disease causing microbes.

 

The ABO blood system

This is a controlled by a tri-allelic gene. It can generate 6 genotypes.

The alleles control the production of antigens on the surface of the red blood cells. Two of the alleles are co-dominant to one another and both are dominant over the third.

Blood Groups

Note:

Blood types A and B have two possible genotypes - homozygous and heterozygous.

Blood types AB and O only have one genotype each.

 

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