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Biochemical Genetics

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. Progeny were all Tall >. Mendel made a cross between a Tall

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Biochemical Genetics

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  1. Biochemical Genetics “The study of the relationships between genes and enzymes, specifically the role of genes in controlling the steps in biochemical pathways.”

  2. Gregor Mendel’s Pea Studies

  3. Mendel’s Seven Traits

  4. Progeny were all Tall > Mendel made a cross between a Tall plant and a Dwarf plant. X

  5. Then, Mendel allowed the plants to self-pollinate: Offspring were: 75% Tall 25% Dwarf How could such a thing happen?

  6. 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

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

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

  9. Gibberellin Hormone

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

  11. 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 !

  12. Finally, a biochemical explanation for Dominance!!!

  13. Dr. Reid found it using Arabidopsis mutant Gibberellin Mutant

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

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

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

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

  18. Starch Grains Made by Starch Synthase and Starch-Branching Enzyme

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

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

  21. Wrinkled seeds are low in starch and high in sugar

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

  23. 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).

  24. 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 Peaβ-Hydroxylase gene for instance is fairly similar to the ones in Tobacco and Lettuce, but much more different than the one in Cucumber.

  25. Kiwi (Actinidia deliciosa) = interspecific hybrid from China Hexaploid = 174 chromosomes (29 pairs)

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