Genetics 371B Lecture Notes: Cancer Genetics, Mitochondrial DNA, Developmental Genetics, Lecture notes of Genetics

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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?

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 x F

“F 1 ”

“F 2 ”

Prediction: The F2 “Purple” class consists of two subclasses:

Conclusions:

1. Determinants are particulate
2. They occur in pairs ; one member may be dominant
3. Determinants segregate randomly into gametes

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

Pedigree analysis

What are pedigrees?

Why bother with them?

Constructing pedigrees “The inability to smell methanethiol is a recessive trait in humans. Ashley, Perry, and Gus are three smelling children of Erin (a non-smeller) and Darren (a smeller). Perry's only child is a non-smeller boy. Construct a pedigree for this family, indicating the genotypes where possible.”

To be continued…

Do all human traits show simple Mendelian inheritance?

Expressivity

Penetrance

Complications

Modified monohybrid ratios Genetics 371B Lecture 3 29 Sept. 1999

Snapdragon flower color

Red flowers White flowers

Pink flowers Blending of determinants??

How to test?

Prediction?

x

... a case of incomplete dominance

e.g., Tay Sachs disease

Symptoms: extreme sensitivity to noise muscle weakness cherry-red spot on retina

Affected individuals rarely survive past childhood

Defect –

Incompletely dominant or recessive?

... in the eye of the beholder?

Overt phenotype...

At the biochemical level...

The curious case of the yellow mice

Normal x Yellow mice

1:1 Normal : Yellow

Yellow x Yellow

2:1 Yellow : Normal

Interpreting: Which allele is dominant?

Parental genotypes?

What’s missing in F2?

The physical basis of Mendelian genetics

1902: Boveri and Sutton, “Chromosome theory of inheritance”

Diploid vs. haploid chromosome number

Chromosomes

What’s in a chromosome?

Protein

The experiment

Bacteriophage with radioactive DNA

Bacteriophage with radioactive protein

Infect bacteria (E. coli)

Do progeny virus have radioactive DNA?

Do progeny virus have radioactive protein?

Conclusion:

The cell cycle Genetics 371B Lecture 4 1 Oct. 1999

The structure of DNA

phosphate ribose sugar

5' 3'

3' 5'

A G T C T T C A G A

Backbone

Pairing