Mendelian Genetics notes, Lecture notes of Genetics

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Mendelian Genetics

Chapter 12, part 1

Gregor Mendel

• (^) Born in 1822 in Moravia (now part of the Czech Republic.
• (^) Son of a tenant farmer; joined a monastery to get an education.
• (^) Deeply interested in science, particularly heredity.

• (^) What was understood at the time:
  • (^) Heredity appeared random and unpredictable.
  • (^) Many traits seemed to blend in the offspring, suggesting a liquid factor controlled heredity.
  • (^) Yet some traits, such as red hair, did not blend away.

• (^) With Abbot Napp’s encouragement, Mendel studied heredity in peas, carefully choosing traits that did not appear to blend. Collected data from 1856 -
• (^) Mendel’s creative contribution: he was the first to follow single traits from generation to generation instead of trying to document and follow every trait in the plants.

• (^) In 1868, Mendel became abbot of his monastery.
• (^) His religious work left little time for research, which he set aside, though he was always convinced he had made a valuable contribution to science.

• (^) Mendel died in 1884. Sixteen years later, in 1900, his work was rediscovered by Hugo de Vries and others looking for clues into the puzzle of heredity.
• (^) Though criticized in some details, the main body of Mendel’s work still stands.

Three Laws of Heredity

• (^) Law of ___________
• (^) Law of ___________
• (^) Law of ____________ ____________

Law of Dominance

• (^) Traits are controlled by two factors that can be called “dominant” or “recessive.”
• (^) A “dominant” trait shows if the offspring inherits __ _____ ___ ________ ______ from one parent.
• (^) A “recessive” trait shows only if the offspring inherits ___ ________ ______ , one from each parent.

X In this cross between two purple-flowered pea plants, one-quarter of the offspring have white flowers. Based just on this information, which is dominant: white or purple flowers? How do you know? Hint: “Dominance” is not based on numbers of individuals with the trait. It is based on the number of copies of the allele that must be inherited to show the trait.

The offspring of a purple-flowered pea plant and a white-flowered pea plant all have purple flowers. The purple trait is dominant. Why? true-breeding, purple-flowered plant First-generation offspring (F 1 ) Parental generation (P) pollen pollen cross-fertilize true-breeding, white-flowered plant

The purple-flowered trait is dominant because each an individual who inherits at least one copy of the purple allele (R) shows the purple phenotype. The white-flowered trait is recessive because an individual must inherit two copies of the white allele (r) to show the white phenotype. genotypes: phenotype

Solving problems involving dominance Dexter has freckles. So does his wife, Darla. Their son, Derek has no freckles. Is having freckles a dominant or a recessive trait?

_____________ parent gametes A A A A In modern terms, the ______________ parents in the P generation can pass on one kind of allele to their offspring. Homologous chromosomes gene

The ______________ parents of the F1 generation have two alleles for the gene in question, and can pass one or the other, but not both, to their offspring. ____________ parent gametes A a A a Homologous chromosomes gene