Monday 7th November COPY LO: To be able to describe and predict outcomes for co-dominance and multiple alleles Starter Guinea pig sheet

BATS Explain how co-dominance affects the inheritance of characteristics Explain how multiple alleles affects inheritance Explain how blood groups in humans is inherited.

Co-dominance = where both alleles are equally dominant This means that both alleles are expressed in the phenotype

Snapdragon plant One allele codes for an enzyme that catalyses the formation of a red pigment The other allele codes for an altered enzyme that lacks this catalytic activity and so does not produce the pigment If they showed the normal pattern for inheritance - what colours could the flowers have?

As they are co-dominant - what colours do we see? 1. If plants are homozygous for the first allele? 2. If plants are homozygous for other allele? 3. In Heterozygous plants?

Why can’t we use upper and lower case letters for these genetic diagrams? Instead we use different letters - in this case R for Red and W for White and put them as superscripts on a letter that represents the gene - e.g. C for colour

Allele for Red pigment = C R Allele for no pigment = C W Book Page Fig 2 & 3 Roan cattle example sheet GENETICS sheet with monohybrid examples

Multiple Alleles - this is when a gene has more than 2 alleles Human ABO Blood Groups 3 alleles associated with the gene I (immunoglobulin gene) which lead to the production of different antigens on the surface membrane of red blood cells

- allele I A, which leads to the production of antigen A - allele I B, which leads to the production of antigen B - allele I O, which does not lead to the production of either antigen

Only 2 of them can be present in an individual as there are only 2 gene loci The alleles I A and I B are co- dominant I O is recessive to both

Possible genotypes of blood groups in the ABO system Blood GroupPossible genotypes AI A I A or I A I O BI B I B or I B I O ABIAIBIAIB OIOIOIOIO

Draw a diagram to show the cross between a person who is blood group O and one who is blood group AB Do any of the offspring have the same blood groups as the parents?

Draw a diagram to show the cross between a person who is blood group A and one who is blood group B What blood groups do their offspring have? Monohybrid cross with multiple alleles sheet - blood groups etc.

Multiple Alleles and a dominance hierarchy Sometimes multiple alleles have a hierarchy of dominance - e.g. in rabbit coat colour The gene for coat colour (C) has 4 alleles

Here they are in the order of dominance: Agouti coat (C A ) Chinchilla coat (C Ch ) Himalayan coat (C H ) Albino coat (C a ) Copy the table opposite and write out the possible genotypes of the rabbits with each coat colour. Coat Colour Possible genotypes Full colour (Agouti) Chinchilla Himalayan Albino

Question 1-3 at bottom of Page 123 Application Page 124

Other useful Sources - summary of Mendelian inheritance The best A Level Biology Website References Glenn Toole, Susan Toole (2008). A2 Biology. Cheltenham: Nelson