Co-dominance
By: M (athilde) dawg, L (iam) dawg, and G (eorge) dawg
Objectives
• 4.3.3 – Multiple alleles
• 4.3.4 – Describe ABO blood groups as an example of
co-dominance and multiple alleles.
• 4.3.5 – Sex Determination
• 4.3.6 – State that some genes are present on the Xchromosome and absent from the shorter Y
chromosome in humans.
4.3.3
• Some genes have more than two alleles.
• An individual can only possess two alleles.
• The population may contain many alleles for a given
gene.
• Multiple alleles increases the number of different
phenotypes.
• Multiple alleles can be dominant, recessive or codominant to each other.
Video
http://www.youtube.com/watch?v=mFbwOubQMgQ&l
ist=ECE7B097006D38E249
4.3.4
-The ABO blood type system in humans has 4 possible phenotypes: A, B, AB,
and O.
-The red blood cell antigen is coded for by the gene I
-I has three alleles three alleles IA, IB and IO
-IA and IB are codominant, while IO is recessive.
The Possible Genotypes
and Phenotypes
The cross below shows how all four blood groups can
arise from a cross between a group A and a group B
parent.
4.3.5
• Determined by sex chromosomes
• X and Y
• In humans:
- Homologous (XX) are females
- Non- Homologous (XY) are males
Monohybrid cross
• Demonstrates inheritance of X and Y chromosomes
• There will be 1:1 ratio of male to females
X and y
• Sex is determined solely by the sperm
• Technique for separating X and Y sperm is using IVF
4.3.6
• These are called sex or linked X-linked genes
• Female sex chromosomes are XX
• Male sex chromosomes are XY
• The Y chromosomes does not carry an allele
reference
• http://static.ddmcdn.com/gif/blood-cells.jpg
• http://2.bp.blogspot.com/fnma529dqx0/URDOSarqpjI/AAAAAAAAADs/gxr1PLCKyyc
/s1600/1-absolutely-innocent-princess1-baby-girl.jpg
• http://2.bp.blogspot.com/-bpJf-4I0toQ/T7Zs9UUBRI/AAAAAAAAAEo/lxo88YNM40s/s1600/Blog+10.jpg
• http://imgc.artprintimages.com/images/art-print/victor-habbickconceptual-image-cloning-where-we-see-cloned-babies-against-aforeground-of-x-and-y-chromosomes_i-G-64-6462-1AVH100Z.jpg
• http://i.telegraph.co.uk/multimedia/archive/01084/educationgraphics_1084561a.jpg
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