Biochemical

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Biochemical Genetics
The study of the relationships between genes and
enzymes, specifically the role of genes in
controlling the steps in biochemical pathways.
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Gregor Mendels Pea Studies
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Mendels Seven Traits
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Mendel made a cross between a Tall plant and a
Dwarf plant.
X
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Then, Mendel allowed the plants to self-pollinate
Offspring were 75 Tall 25 Dwarf
How could such a thing happen?
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Alleles are often indicated with a single
letter. A CAPITAL letter denotes a dominant
allele T A lowercase letter denotes a recessive
allele t
Genotype (chemical code)
Phenotype (visual)
TT x tt
Tt
Tall x Dwarf
Tall
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one parent (female)
T
t
T
TT
Tt
25 TT (tall) 50 Tt (tall) 25 tt (dwarf)
t
Tt
tt
..other Parent (male)
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Dr. James Reid University of Tasmania discoverer
of the le mutation
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Gibberellin Hormone
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Gibberellin 3 beta-hydroxylase is non-functional
in this mutant
The Active form Of Gibberellin
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• The le allele is a point mutation (substitution)
• that alters the active site of the enzyme.
• Which explains the differences seen between
  heterozygotes and homozygous-recessives !
• 
  

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Finally, a biochemical explanation for
Dominance!!!
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Dr. Reid found it using Arabidopsis mutant
Gibberellin
Mutant
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Pea Arabidopsis
le mutation
Iron-binding cofactor sites
Mutation of Active Site
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Pea Arabidopsis
Probably NOT in these four conserved areas
Where could neutral mutations occur?
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Mendels Seven Traits
Another example of using Biochemical Genetics
to explain Mendels observations
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pea
corn
The wrinkled seed trait in plants Smooth seed
is dominant over wrinkled seed Why?
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Starch Grains
Made by Starch Synthase and Starch-Branching
Enzyme
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r is the gene described by Mendel
r stands for rugosus wrinkled
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Wrinkled seeds are low in starch and high in
sugar (starch is a polymer of glucose)
Starch synthesis in developing seeds
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Wrinkled seeds are low in starch and high in
sugar
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It all has to do with Osmosis diffusion of
water across a membrane from high concentration
to low concentration
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Sugars build-up because they are not being used
to make starch.
Starch-Branching Enzyme is mutated (Loss of
Function)
Water moves into cells of seed due to osmosis.
Later, as seeds mature, they dry down (so
they can survive long periods).
Tissue swells
Dry seeds end up looking wrinkled (like a
raisin).
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So what?
Could try to overcome mutation in pea or other
plants.
Could induce mutation in other species.
Learn about the function of the enzyme.
Learn about similar genes in other species
The Pea ß-Hydroxylase gene for instance is fairly
similar to the ones in Tobacco and Lettuce,
but much more different than the one in
Cucumber.
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Kiwi (Actinidia deliciosa) interspecific
hybrid from China Hexaploid 174 chromosomes
(29 pairs)