Co dominance & Multiple Alleles L.O: to solve a codominant cross to solve a multiple allele cross to create synoptic links to other topics Starter: SpongeBob Squarepants Genetics worksheet!

Co dominant Crosses A type of monohybrid cross, so still only looking at one gene BUT two alleles are expressed! How to Solve a Co dominant Cross 1)The gene has a capital letter 2)The alleles are written in superscript 3)Write the parents alleles in the punnett square 4)Solve the genotypes and phenotypes of the offspring 5)Calculate the ratio / %

Worked Example: Coat colour in cows

Your turn… Snapdragons show co dominance. P R is red petals, P W is white petals and a combination of both is pink. Draw a monohybrid cross between two heterozygous parents and write the ratio of the phenotypes produced.

Multiple Alleles A type of monohybrid cross, so still only looking at one gene BUT there are three alleles or more, and only two can be expressed. How to Solve a Multiple Allele Cross 1)The gene has a capital letter 2)The alleles are written in superscript 3)Write the parents alleles in the punnett square 4)Solve the genotypes and phenotypes of the offspring 5)Calculate the ratio / %

Worked Example: Human Blood Group Different allele creates a different antigen on the surface membrane of red blood cells.

Your Turn… a)Cross between I A I B and I O I O b)Cross between I A I O and I B I O

Synoptic Links 1) Research which blood groups can donate to whom. You will need to understand why (there is a link to a previous module in AS) Further research: a)Which blood group is most common in Europe, compared to Africa? b)What is hemolysis? c)What is hemolytic disease of the newborn?