Transcript Co dominance - The Grange School Blogs

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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
R
C
Allele for Red pigment =
W
Allele for no pigment = C
Book Page 122 - 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
A
I ,
- allele
which leads to the
production of antigen A
B
- allele I , which leads to the
production of antigen B
O
- allele I , 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
A
I
B
I
and
are codominant
•
O
I
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:
A
Agouti coat (C )
Chinchilla coat
(CCh)
Himalayan coat
(CH)
Possible
Coat Colour
genotypes
Full colour
(Agouti)
Albino coat (Ca)
Chinchilla
Copy the table
opposite and
write out the
possible
genotypes of the
rabbits with each
coat colour.
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