Incomplete and codominance
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Transcript of Incomplete and codominance
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DOMINANCE
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INCOMPLETE DOMINANCE
• Pattern of gene expression in which the phenotype of a heterozygous individual is intermediate between those of the parents.
• Cases in which one allele is not completely dominant over another.
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• Snapdragons
http://faculty.pnc.edu/pwilkin/incompdominance.jpg
http://www.dobermann-review.com/info/genetics/mendels_genetic_laws/Gregor%20Mendel.jpg
HUH?
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Incomplete Dominance
X
R1
R2
F1
F2R2R2 does not produce pigment
Heterozygote only produces ½ pigment of R1R1
http://www.google.ca/images?hl=en&q=incoplete%20dominance&rlz=1W1SNNT_enCA397&um=1&ie=UTF-8&source=og&sa=N&tab=wi&biw=1345&bih=555
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http://2.bp.blogspot.com/_uPFMFfHgGGg/SygBEtl5D1I/AAAAAAAAAKc/nylZiiL2k7s/s320/incomplete+dominance.jpg
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CODOMINANCE
• The condition in which both alleles in a heterozygous organism are expressed.
• BOTH alleles contribute to the phenotype.
• The two alleles don’t blend, but are rather both present in the offspring.
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http://search.vadlo.com/b/q?rel=2&keys=Dominance+Incomplete+Dominance+Codominance+PPT
Roan Horse
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Roan Cattle
Variegated Clover
http://3.bp.blogspot.com/_zUPrgMM5tUg/SSVdrs59_uI/AAAAAAAAAA8/qJGjG2nZPhk/s200/codominance.GIF
http://www.ccs.k12.in.us/chsteachers/BYost/Biology%20Notes/CH11notescoincompletedom_files/image004.jpg
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MULTIPLE ALLELISM
• When there is more than 2 alleles possible for a given gene.
• Allows for a larger number of genetic and phenotypic possibilities.
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CODOMINANCE & MULTIPLE ALLELES
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BLOOD TYPES
Antibody Anti – B Anti – A
None
Anti – A, Anti – B
• 4 ABO blood types•3 alleles of the I gene
IA = A antigen on RBCIB = B antigen on RBCi = neither A nor B antigen
Genotype IAIA or IAi
IBIB or IBi
IAIB
ii
Blood type AB
AB
O
http://sydfish.files.wordpress.com/2008/02/bloodcells.jpg
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http://image.wistatutor.com/content/feed/tvcs/blood_type5B15D.jpg
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http://www.biologycorner.com/anatomy/blood/images/bloodtypes.jpg
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Codominance & Multiple Alleles• Human blood type is
an example of both codominance and a trait with multiple alleles.
• AB = universal acceptor
• O = universal donor
BLOOD TYPE
GENOTYPE CAN RECEIVE BLOOD FROM
A IAIA , IAi A, O
B IBIB , IBi B, O
AB IAIB A, B, AB, O
O ii O
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Rhesus Factor
• The Rhesus factor, also known as the Rh factor, gets its name from experiments conducted in 1937 by scientists Karl Landsteiner and Alexander S. Weiner.
• Involved Rabbits which when injected with the Rhesus monkey’s red blood cells, produced an antigen present in the red blood cells of many humans
http://content9.clipmarks.com/blog_cache/latimesblogs.latimes.com/img/E0C83714-56E5-4757-B9F1-604FCE5643C3
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Rhesus Factor• The Rhesus factor is an antigen, or more
specifically a protein, that exists on the surface of red blood cells.
• If a person has either two (+) genes for Rh or one (+) and one (-) Rh gene, they will test Rh(+). A person will be negative only if they have 2 (-).
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• It is very important in terms of babies: E.g. an Rh(-) mother may make antibody against an Rh(+) fetus if the baby gets a (+) gene from its father (Obstetricians screen pregnant women for this problem with blood tests).
• The ABO and RH genes are only two of many blood antigens that are present on human red cells and must be matched up for successful blood transfusions.
Relevance of Rh Factor & ABO Typing?
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Multifactorial
• Referring to control of the expression of a trait by several genes and environmental factors.
• Many multifactorial traits show continuous distribution.
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Multifactorial
• E.g. Human height usually between 120cm and 200cm, however these genes cannot be fully expressed without all the necessary nutrients from a healthy diet
http://www.babble.com/CS/blogs/droolicious/menace-height.jpg
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PRACTICE QUESTIONS 1. In a certain case a woman’s blood type
was tested to be AB. She married and her husbands blood type was type A. Their children have blood types A, AB, and B. What are the genotypes of the parents? What are the genotypic ratios of the children?
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2. In a certain breed of cow the gene for red fur, R, is codominant with that of white fur, W. What would be the phenotypic & genotypic ratios of the offspring if you breed a red cow and a white bull? What would they be if you breed a red & white cow with a red & white bull?
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3. A rooster with grey feathers is mated with a hen of the same phenotype. Among their offspring 15 chicks are grey, 6 are black and 8 are white.
a. What is the simplest explanation for the inheritance of these colors in chickens?
b. What offspring would you expect from the mating of a grey rooster and a black hen?