An Example of Complex Genetics Inheritance of Types An Example of Complex Genetics

Intro to Blood Types Blood types are described with both a letter and a + or – sign (A+, O-, etc.) that name the kinds of marker proteins found on blood cell membranes We will only examine the letters here The + or – sign refers to “Rh positive or Rh negative” (this tells whether or not the blood cells have marker proteins on them that were first described in rhesus monkeys)

Percent of People with each Blood Type in the US

Blood Type Inheritance Blood type inheritance is a double exception to Mendel’s Law of Dominance First, there are three possible alleles for blood type in the human gene pool: A, B, and O (but any one person only gets two of them) Second, A and B are codominant alleles (both are expressed simultaneously) These result in 4 possible phenotypes: Type A blood (Dominant allele) Type B blood (Also Dominant) Type AB blood(Codominant) Type O blood (Recessive allele)

Possible blood type genotypes and phenotypes Blood type alleles are shown with the letter I for “Immune Response” since mixing the wrong blood types causes one type to attack the other (this is an immune response using antibodies to attack the foreign blood cells) Type A allele = IA Type B allele = IB Type O allele = iO Heterozygous Geno Pheno Homozygous Geno Pheno IAiO IAIA Type A Type A IBiO Type B IBIB Type B IAIB Type AB iOiO Type O

What happens if the wrong blood types mix? Red blood cells have marker proteins on their membranes that show if they are Type A or Type B – there is not a Type O marker protein These marker proteins are called “antigens,” since they can generate an immune response If the wrong blood type is given to someone, their antibodies attack the foreign antigens – this makes the blood clump together, or “agglutinate.” This is not good for keeping your blood flowing to your organs! Normal Blood Agglutinated Blood

What happens if the wrong blood types mix? This red blood cell has Type A antigens – it will be attacked by “Anti-A” antibodies found in Type B and Type O blood B This red blood cell has Type B antigens – it will be attacked by “Anti-B” antibodies found in Type A and Type O blood This red blood cell has Type A and Type B antigens – it will be attacked by “Anti-A” antibodies found in Type B and Type O blood and by “Anti-B” antibodies found in Type A and Type O blood – but it won’t attack it’s own kind, so it can get blood from anyone! B A This red blood cell has NO antigens – it will not be attacked by any kind of blood, so it can give blood to everybody – but it can only receive blood if there are no markers on the cells. This is Type O blood.

Summary of Blood Type Characteristics (Phenotype) Alleles (Genotype) Antigens (Marker Proteins) Anti- Bodies Receives From Donates To A IAio or IAIA Anti-B A or O A or AB B IBio or IBIB Anti-A B or O B or IAIB Both A and B none All!! “Universal Receiver” O ioio None Both Anti-A & Anti-B “Universal Donor”