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 Tall plant 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 = T A lowercase letter denotes a recessive allele = t TT x tt Tt Tall x Dwarf Tall Genotype (chemical code):Phenotype (visual):

T t T t TTtTt TtTt t …one parent (female)..other Parent (male) 25% TT (tall) 50% Tt (tall) 25% tt (dwarf)

Dr. James Reid University of Tasmania discoverer of the le mutation

Gibberellin Hormone

The Active form Of Gibberellin Gibberellin 3 beta-hydroxylase is 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 of using “Biochemical Genetics” to explain Mendel’s observations

The wrinkled seed trait in plants “Smooth seed” is dominant over wrinkled seed Why? corn pea

Made by Starch Synthase and Starch-Branching Enzyme Starch Grains

“r” is the gene described by Mendel “r” stands for “rugosus” = “wrinkled”

Wrinkled seeds are low in starch and high in sugar (starch is a polymer of glucose) Starch synthesis in developing seeds

Wrinkled seeds are low in starch and high in sugar

It all has to do with Osmosis “diffusion of water across a membrane from high concentration to low concentration”

Starch-Branching Enzyme is mutated (Loss of Function) Sugars build-up because they are not being used to make starch. Water moves into cells of seed due to osmosis. Tissue swells Later, as seeds mature, they dry down (so they can survive long periods). Dry seeds end up looking 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)