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 = CR

Allele for no pigment = CW

Book Page 122 - Fig 2 & 3Roan cattle example sheetGENETICS 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 IA, which leads to the production of antigen A

- allele IB, which leads to the production of antigen B

- allele IO, 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 IA and IB are co-dominant

•IO is recessive to both

Possible genotypes of blood groups in the ABO system

Blood Group Possible genotypes

A IAIA or IAIO

B IBIB or IBIO

AB IAIB

O IOIO

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 (CA)

•Chinchilla coat (CCh)

•Himalayan coat (CH)

• Albino coat (Ca)

•Copy the table opposite and write out the possible genotypes of the rabbits with each coat colour.

Coat Colour

Possible genotype

sFull colour (Agouti)

Chinchilla

Himalayan

Albino

Question 1-3 at bottom of Page 123

• Application Page 124

Other useful Sources

http://www.youtube.com/watch?v=NgXOLU3uiHg - summary of Mendelian inheritance

http://www.biologymad.com/master.html?http://www.biologymad.com/A2Biology.htm The best A Level Biology Website

References Glenn Toole, Susan Toole (2008). A2 Biology. Cheltenham: Nelson