Co- dominance WALT That some alleles show incomplete dominance That some alleles show co-dominance

Incomplete dominance Where the action of one allele does not mask the action of another Neither allele has dominant control over a particular characteristic The heterozygous offspring have an intermediate phenotype between the contrasting parents

The snapdragon An example of incomplete dominance is the snapdragon When red and white flowered flowers are crossed The resulting offspring are all ……………..

Pink!! Draw the cross of the red and white flowered snapdragon What would the F1 cross produce?

F1 Cross × Gametes

A plant breeder wants to produce flowers that are only pink or white Determine the phenotypes of the parents necessary to produce these desired offspring. Use a punnet square Gametes

Co dominance This is where two alleles in a heterozygous organism contribute equally to the phenotype Both alleles are independently and equally expressed An examples of this is the human blood group AB where both alleles are equally expressed

Multiple Alleles In humans the inheritance of the ABO blood group is determined by a gene – symbol I which has 3 different alleles. The ABO antigens consist of sugars attached to the surface of RBC The alleles code for enzymes that join together these sugars

Allele I A causes production of antigen A on RBCs Allele I B causes production of antigen B on RBCs Allele I O causes no production of antigens on RBCs Alleles I A and I B are codominant and allele I O is recessive to both

For each blood group A, B, AB and O work out the possible genetypes Blood group Possible genotypes A I A I A or I A I O B I B I B or I B I O AB I A I B OIOIOOIOIO

The transmission of these alleles occurs in normal Mendelian fashion.

A cross between certain individuals of blood group A and certain individuals of blood group B may produce offspring with any one of the 4 blood groups: