Gregor Mendel

- Father of genetics Presented the laws of inheritance by studying pea plants. Proposed that invisible internal units of information account for observable traits, and that these factors (later known as genes) are passed from one generation to the next.

Walther Flemming

Reported his discovery of chromosomes and mitosis

DNA

- A carrier of genetic inheritance passed from one generation to the next. - A nucleic acid made of 4 nucleotides (ATGC) , each containing a phosphate group, deoxyribose sugar (pentose sugar) and a nitrogenous base (purines and pyrimidines) - Composed of 2 strands of complementary nucleotides forming a double helix. Strands are antiparallel: One strand runs 5' to 3' and the other is 3' to 5'. 1 strand determines the other - Only molecule that can replicate (makes 2 copies out of 1) - P and S form backbone of DNA A+T and G+C pairings of nucleotides through HYDROGEN BONDING

Chromosomes

Contain protein and DNA - Tightly packaged bundle of DNA that contains many genes 46 chromosomes arranged in 23 pairs - one chromosome of each pair is from the mother, and the other one is from the father

Gene

a unit of heredity that is transferred from parents to offspring that determines some traits of the offspring. - A section of DNA that contains instructions for a trait EX) Blood type, hair colour, and eye colour.

Allele

One of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome - Can be dominant or recessive - Inherit one from each parent EX) A blood type, brown hair colour, and blue eye colour.

James Watson and Francis Crick

Proposed the double helix structure of DNA and that DNA replication was semi-conservative - their double helix model was influenced by Rosalind Franklin's x-ray data.

Rosalind Franklin

Used x-ray diffraction to reveal DNA's double helix structure

What was known before the discovery of DNA?

1. Genes are associated with specific traits 2. Genes were known to be carried on chromosomes 3. The chromosomes were found to consist of DNA and protein

Traits

- Specific characteristics of an individual determined by genes and the environment -Can be qualitative (trait is influenced by a single gene, not influenced by environment EX. eye colour) or quantitative (influenced by many genes and the environment EX. height and weight)

Griffith's experiment

Purpose: to understand how some bacteria caused disease while others didn't Experiment: involved S strain and R strain. S caused disease, R didn't. He injected mice with the different forms of the bacteria and found: Live S = Mouse died Live R = Mouse lived Denatured S - Mouse lived Denatured S + live R = Mouse died Result: Live R bacteria changed into disease causing S bacteria even though the S had been killed by heat, suggesting that the dead S strain passed a heritable substance to the living R strain, changing its characteristics. He was able to recover living S strain from the dead mouse, and since the S strain was killed by high temp., proteins couldn't have been the carrier of genetic info.

Avery MacLeod and McCarty Experiment

Repeated Griffiths experiment Purpose: To find what carries genetic material Experiment: Killed s strain and live r strain = mouse dies (control group) Destroyed polysaccharides = mouse dies because genes from S strain still survived = polysacs NOT genetic info Destroyed lipids = mouse dies = lipids not genetic info RNA destroyed = mouse dies = RNA not genetic info Protein destroyed = mouse dies = protein not genetic info DNA destroyed on S strain = mouse lives = genetic info Result: DNA is the genetic material

Hershey and Chase

Purpose: Is DNA or protein the genetic material Experiment: Used radioactive labels to track DNA and protein in a macrophage DNA labelled with radioactive phosphorus Protein labelled with radioactive sulfur Allowed viruses to infect bacteria and then separated the virus articles from the bacteria Result: Radioactive DNA was found in the bacteria and radioactive protein was found outside the bacteria meaning DNA enters cells and provides genetic instructions for making new viruses. CONCLUSION: DNA is the genetic material, NOT protein

Purines

Nucleotides (building blocks of nucleic acids) Adenine and Guanine Have fused double ring nitrogenous base

Pyrimidines

Nucleotides (building blocks of nucleic acids) Cytosine and Thymine

Chargaff's empirical rules of base composition

1. the total amount of pyrimidine nucleotides (T + C) always equals the total amount of purine nucleotides (A + G). 2. the amount of T always equals the amount of A, and the amount of C always equals the amount of G. But the amount of A + T is not necessarily equal to the amount of G + C. EXAMPLE: A=T G=C All four bases = 100% if G+C = 56% that means that: G=28% and C=28% Find the remaining % - total must be 100% - 100% - 56% = 44% So: A + T = 44% and because A=T - A=22% T= 22%

Before DNA structure was discovered, 3 properties of the hereditary material were proposed

1. Because essentially every cell in the body of an organism has the same genetic makeup, faithful replication of the genetic material at every cell division is crucial. -DNA must be copied accurately because when a cell divides, it needs to make a copy of its DNA so each new cells gets the same genetic info 2. Because it must encode the constellation of proteins expressed by an organism, the genetic material must have informational content. - DNA must contain instructions that tell the cell how to make the proteins it needs. 3. Because hereditary changes, called mutations, provide the raw material for evolutionary selection, the genetic material must be able to change on rare occasion. Nevertheless, the structure of DNA must be stable so that organisms can rely on its encoded information. -DNA needs to stay mostly unchanged so that genetic information can be passed from parents to offspring accurately but it also needs to be flexible enough to allow mutations and evolution SUMMARY: 1. DNA needs to replicate so new cells get the same genetic info 2. Store info so cells know how to make the necessary proteins 3. Stable but changeable so info is preserved but mutations can allow evolution

Semi-conservative replication

DNA replication is semi-conservative - Every double helix in the new generation of an organism consists of one complete old strand and one complete new strand wrapped around each other EXAMPLE: 1. DNA zipper unzips 2. Each old strand acts as a template 3. A new matching strand is synthesized onto each old side 4. End with 2 DNA molecules, each containing one old strand and one new strand

Conservative replication

the old DNA is used as a template only and is not incorporated into the new double-helix. Thus the new cell has one completely new double-helix and one completely old double-helix.

Dispersive (mosiac) replication

a final product in which each double helix of DNA is a mixture of fragments of old and new DNA

Meselson Stahl experiment

Purpose: To determine the correct model for DNA replication (semi-conservative, conservative, or dispersive) Experiment: Grew bacteria in a form of nitrogen that is heavier than normal nitrogen, meaning the bacteria DNA became heavy. They moved the bacteria into normal N and allowed them to reproduce. They examined the DNA after each generation using density-gradient centrifugation which separates DNA based on how heavy it is. Results: Before replication: Heavy DNA After 1 generation: Hybrid DNA (one old heavy strand and one new light strand) After 2 generations: 50% hybrid DNA 50% light DNA Conclusion: The results match the semi-conservative model