Biochemical Genetics The study of the relationships between

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

Mendel made a cross between a Tall plant and a Dwarf plant. X 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 Genotype (chemical code): TT x Tt tt Phenotype (visual): Tall x Tall Dwarf

…one parent (female) T t T TT Tt tt . . 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

Gibberellin 3 beta-hydroxylase is non-functional in this mutant The Active form Of Gibberellin

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!!!

Dr. Reid found it using Arabidopsis mutant Gibberellin Mutant

Pea Arabidopsis le mutation Iron-binding cofactor sites Mutation of Active Site

Pea Arabidopsis Probably NOT in these four “conserved” areas Where could neutral mutations occur?

Mendel’s Seven Traits Another example of using “Biochemical Genetics” to explain Mendel’s observations

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

Starch Grains Made by Starch Synthase and Starch-Branching Enzyme

“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. Later, as seeds mature, they dry down (so they can survive long periods). Dry seeds end up looking wrinkled (like a raisin). Water moves into cells of seed due to osmosis. Tissue swells

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)