Genetics Overview Notes

Topics: Genetics, Gene, Chromosome Pages: 22 (5061 words) Published: February 4, 2013
* Proteins were originally thought to be the molecule of heredity because they were more complex than DNA, were very present, and DNA was only found on chromosomes * * S type → dead mouse

* R type → healthy mouse
* S type (heat killed) → healthy mouse→ no S cells isolated from mouse * S type (heat killed) plus R → dead mouse

* S type → dead mouse
* R type → healthy mouse
* S type (heat killed) → healthy mouse→ no S cells isolated from mouse * S type (heat killed) plus R → dead mouse

Three key genetic experiments:
1. Griffith (1928) – streptococcus and mice
* Conclusion: something in dead S cells forced R cells to transform, but transformative substance (DNA) was not discovered until much later 2. Avery, McLeod, & McCarthy (1944) – discovered that DNA was responsible for heredity * Treated heat-killed S type with:

1. RNAase for RNA → R + S colonies (transformation)
2. Proteinase for protein → R + S colonies (transformation) 3. DNAase for DNA → R but no S (no transformation)
3. Hershey-Chase (1952) – radioactively labeled DNA and proteins separately in E. coli * Attached phosphorus to DNA and sulfur to proteins (of phages) * Resulting offspring had phosphorus but no sulfur

* Thus supporting the hypothesis that DNA was responsible for heredity * * Strands are anti-parallel (pair in opposite directions)

* Strands are anti-parallel (pair in opposite directions)

Watson, Crick (1953), Wilkens, & Franklin – responsible for discovery of double helix (sugar backbone & paired nucleotides A/T and C/G) * DNA has directionality from polarity
* Starts at 5’ end with phosphate
* Ends at 3’ end with hydroxyl
* Discovery showed that nucleotide sequence could:
1. Be copied.
2. Code for information.
3. Result in errors as a result of base changes (mutations). * Remember: genes code for specific proteins, which is how genes exert effect on organisms indirectly * Prof. Garrod (1908) proposed that hereditary disease was due to inborn errors of metabolism * Linked defective enzyme to Alkaptonuria (black urine disease) * This disease results from oxidation of homogentisic acid * Beadle and Tatum (1941) – One-Gene-One-Enzyme Hypothesis * Looked at bread molds and mutated spores (fungi)

* Found that mutant asexual spores can grow in complete medium but not in minimal medium * Un-mutated spores grow in both medium
* Gregor Mendel – disproved the theory of blending inheritance * Mendel’s Genetic Hypothesis: factors remain unchanged as they are passed through generations and each parent contributes distinct elements of heredity down, known as factors (or genes) * Chose to use true breeding garden pea plants because: 1. They have many observable, uniform traits.

2. They self-fertilize, but can be artificially fertilized. * Reciprocal cross – a cross between different true-breeding pea varieties in both directions * Mendel’s reciprocal crosses resulted in all F1 progeny showing only 1 parent trait (round v. wrinkled) * Principle of Segregation: genes randomly separate into reproductive cells * Gametes: reproductive cells that contain only 1 copy of the gene, & unite randomly when fertilized * Transposable element: DNA sequence capable of transposing from one location to another * Includes molecular basis of insertion of wrinkled (w) mutation in SBEI, or starch-branching enzyme * Both forms of SBEI gene (W and w) can be seen on gel if gene is co-dominant * Testcross: cross between dominant phenotype of unknown genotype + known homozygous recessive genotype * Used to confirm that F1’s are heterozygotes through observation of different gametes in the progeny generation * Di-hybrid cross: the inheritance of two traits on the same...
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