Introduction – Mendelian inheritance - UW Departments Web ...

[Pages:242]Introduction ? Mendelian inheritance

Genetics 371B Lecture 1

27 Sept. 1999

The mechanism of inheritance... Some early hypotheses:

Predetermination e.g., the homunculus theory

Blending of traits

Introducing a more systematic approach... Gregor Mendel (1822?1884) and his experiments with garden pea

But first: Choosing a model organism

What is it?

Why bother?

Features of a good model organism: Some commonly used model organisms:

Mendel's organism of choice: garden pea His question: If a pair of plant lines showing a clear character difference are crossed, will the progeny show an intermediate phenotype?

He established true-breeding lines...

...that showed character differences

Made crosses (matings) between each pair of lines Example: Character: Phenotypes:

x

"F1" F1 x F1

"F2"

Mendelian Genetics ? Monohybrid cross

Genetics 371B Lecture 2

28 Sept. 1999

Interpreting Mendel's experiment

Parents:

Gametes: F1 progeny: Gametes: F2 progeny:

Conclusions: 1. Determinants are particulate 2. They occur in pairs; one member may be dominant 3. Determinants segregate randomly into gametes Prediction: The F2 "Purple" class consists of two subclasses:

Testing the prediction:

What Mendel did:

What we would do today (hindsight!):

Generality of Mendel's first law: (Not just for pea plants!)

Fruit fly (Drosophila melanogaster) Normal (brown) body x black body

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