biochemical genetics “the study of the relationships between genes and enzymes, specifically the...
TRANSCRIPT
Biochemical Genetics
“The study of the relationships between genes and enzymes, specifically the role of genes in controlling the steps in biochemical pathways.”
Gregor Mendel’s Pea Studies
Mendel’s Seven Traits
X
Mendel made a cross between a Tallplant and a Dwarf plant.
Progeny were all Tall >
Then, Mendel allowed the plants to self-pollinate:
Offspring were:
75% Tall
25% Dwarf
How could such a thing happen?
Alleles are often indicated with a single letter.
A CAPITAL letter denotes a dominant allele = TA lowercase letter denotes a recessive allele = t
TT x tt
Tt
Tall x Dwarf
Tall
Genotype (chemical code): Phenotype (visual):
T
t
T t
TT Tt
Tt tt
…one parent (female)
..other Parent (male)
25% TT (tall)50% Tt (tall)25% tt (dwarf)
Dr. James ReidUniversity of Tasmania
discoverer of the le mutation
Gibberellin Hormone
The Active formOf Gibberellin
Gibberellin 3 beta-hydroxylaseis non-functional in this mutant
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 !
Finally, a biochemical explanation for Dominance!!!
Gibberellin
Mutant
Dr. Reid found it using Arabidopsis mutant
Iron-binding cofactor sites
Mutation of Active Site
Pea
Arabidopsis
le mutation
Where could neutral mutations occur?
Pea
Arabidopsis
Probably NOT in these four “conserved” areas
Mendel’s Seven Traits
Another example ofusing “Biochemical Genetics” to explain
Mendel’s observations
The wrinkled seed trait in plants
“Smooth seed” is dominantover wrinkled seed
Why?
cornpea
Made by Starch Synthase
and Starch-Branching Enzyme
StarchGrains
“r” is the genedescribed by
Mendel
“r” stands for “rugosus” = “wrinkled”
Wrinkled seedsare low in starchand high in sugar
(starch is a polymerof glucose) Starch synthesis
in developing seeds
Wrinkled seedsare low in starchand high in sugar
It all has to do with
Osmosis“diffusion of water across a membrane
from high concentration tolow concentration”
Starch-BranchingEnzyme is mutated(Loss of Function)
Sugars build-up because they are not being used to
make starch.
Water movesinto cells ofseed due to
osmosis.
Tissue swells Later, as seeds mature,they dry down (so they
can survive long periods).
Dry seeds end uplooking wrinkled
(like a raisin).
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 β-Hydroxylase gene for instance is fairly similar to the ones in Tobacco and Lettuce, but much more different than the one in Cucumber.
Kiwi (Actinidia deliciosa) = interspecific hybrid from China
Hexaploid = 174 chromosomes (29 pairs)