Darwin’s Tea PartyDarwin’s Tea Party

The Biological Revolution: The Biological Revolution: DNA and Modern GeneticsDNA and Modern Genetics

Winter 2009Winter 2009

After Mendel After Mendel

• Gregor Mendel (1822-1884) had Gregor Mendel (1822-1884) had discovered the basic mechanisms of discovered the basic mechanisms of heredity. heredity.

• His discoveries also strongly His discoveries also strongly suggested physical or material suggested physical or material particles were responsible for the particles were responsible for the transmission and expression of these transmission and expression of these hereditary characteristics.hereditary characteristics.

The Discovery of DNA The Discovery of DNA

In 1951 James Watson (1928- ) and Francis Crick (1916- ) discovered the structure of the DNA molecule - Deoxyribonucleic Acid

In this famous photograph Watson (right) and Crick (left) demonstrate a model of the DNA molecule.

The Discovery of DNA The Discovery of DNA

DNA was soon shown to be the mysterious material particle sought for since Mendel’s discoveries.

The Discovery of DNAThe Discovery of DNA

DNA exists in the nucleus of almost every cell in the body, beginning from day 1 when you were just an embryo.

Hi Mom!

Cross section of skin, showing skin cells.Cross section of skin, showing skin cells.

DNA is inside the nucleus of a cell, within its chromosomes

The DNA molecule is structured in a “double helix” shape (like two spiraling staircases).

One helix is connected to another by base pairs – shown here as “A”, “T”, “C”, “G”.

DNA Base Pairing RulesDNA Base Pairing Rules

A Japanese molecule

Base pairing rules

The base pairs, though, must connect following the base-pairing rules so that “A” connects only with “T” and “C” with “G”.

DNA sequencesDNA sequences

A DNA sequence is simply the order of base pairs along the DNA

double spiral.

In this case, we note the sequence “T-A” “C-G”

DNA and GenesDNA and Genes

What is a gene?

A gene is thus a segment of DNA containing varying lengths of DNA base pair sequences (T-A, C-G, G-C, T-A, etc…).

Genes and ProteinsGenes and Proteins

Actually, the route from DNA sequence to protein is a bit more complicated. First the DNA sequence spells out a certain type of amino acid and that then helps produce a certain type of protein.

• Different DNA sequences (genes) Different DNA sequences (genes) “spell out” different kinds of “spell out” different kinds of proteins.proteins.

• Proteins are key ingredients Proteins are key ingredients helping to make all sorts of cells helping to make all sorts of cells and cell functions from skin cells, and cell functions from skin cells, to hair cells, to blood products, to to hair cells, to blood products, to various enzymes, to … you name various enzymes, to … you name it. it.

• In this way DNA really is a blue In this way DNA really is a blue print for how to make the proteins print for how to make the proteins & enzymes that go on to make the & enzymes that go on to make the traits of an entire body. traits of an entire body.

Genes and TraitsGenes and Traits

• Thus genetic traits, whether physical Thus genetic traits, whether physical or mental can be traced back to DNA or mental can be traced back to DNA sequences. sequences.

• This is true for “normal traits”, e.g. This is true for “normal traits”, e.g. for hair colour, eye colour, etc… as for hair colour, eye colour, etc… as well as for “abnormal traits”, such as well as for “abnormal traits”, such as some genetic diseases. some genetic diseases.

• Humans have 23 pairs of chromosomes, receiving one pair from each parent.

• Genes are located in particular locations and regions of the chromosomes.

Human Genome Project

• Thanks to the Human Genome Project and other endeavours to “map” the genetic code, we can now detect many genetic anomalies responsible for genetic diseases in humans.

• Here, in specific locations of chromosomes 13 and 17, are the BRCA1 and BRCA2 mutations, responsible for some hereditary forms of breast cancer.

Genes and TraitsGenes and Traits

In this example, the In this example, the genetic disease genetic disease sickle cell anemia sickle cell anemia can be traced back can be traced back to a single genetic to a single genetic “spelling mistake” in “spelling mistake” in the genetic the genetic sequences contained sequences contained in the upper part of in the upper part of chromosome 11: chromosome 11:

Genetic Engineering

Genetic Engineering Genetic Engineering

• Genetic engineering involves modifying Genetic engineering involves modifying sections of the genetic code (gene sections of the genetic code (gene sequences) of an organism. sequences) of an organism.

• This can be done by cutting, copying, This can be done by cutting, copying, changing or inserting desired gene changing or inserting desired gene sequences in the genetic code. sequences in the genetic code.

• Inserting of gene sequences is often Inserting of gene sequences is often done through viruses and bacteria. done through viruses and bacteria.

Genetic EngineeringGenetic Engineering

Genes can control certain traits; as in flower colour in this example.

Genetic engineering: Using bacteria Genetic engineering: Using bacteria

and virusesand viruses Of course, we don’t always associate bacteria and viruses with helpful effects!

Here, for example, are two unhelpful bacteria, the Tobacco Mosaic Virus and Human Immunodeficiency Virus (HIV) which produces AIDS.

The T4 bacteriophage is a virus which attack the E. coli bacteria.

Applications of genetic Applications of genetic engineeringengineering

Gene Gene TherapTherap

yyGenetic engineering techniques can be used for altering genetic sequences responsible for genetic diseases. This is called gene therapy.

In this case, missing sequences causing Cystic fibrosis can be inserted into the genetic code of a CF patient using a virus as delivery vehicle.

Here the gene for producing insulin is taken from a human chromosome and inserted into a bacteria’s plasmid (a single ringed chromosome). This plasmid with the human insulin gene can then be used to produce insulin to treat certain forms of diabetes.

This is one example of how genetic engineering techniques can be used to create pharmaceuticals or medicines.

Genetic engineering of Genetic engineering of pharmaceuticalspharmaceuticals

Genetically modified Genetically modified foodsfoods

But what if we could But what if we could change the genetic change the genetic blue print – the blue print – the genetic sequences genetic sequences that ultimately make that ultimately make up life?up life?

Genetically Modified Foods (GMFs)

Scientists can alter genes by cutting out undesired and inserting desired sequences. In this case a gene from a bacteria called Bt which acts like an insecticide is being inserted into the genetic code of a corn plant. The corn will thus contain this built in insecticide.

http://mathgeeklife.blogspot.com/2007/11/genetic-engineering.htmlhttp://mathgeeklife.blogspot.com/2007/11/genetic-engineering.html

Catfish anyone?

Genetic engineering of Genetic engineering of humans? humans?

Fears of genetic engineering often go back to the Frankenstein story.

Applications of Genetic Applications of Genetic Technology Technology

Thus, many applications of genetic technology Thus, many applications of genetic technology exist, including:exist, including:– Criminal forensics Criminal forensics – Medical DiagnosticsMedical Diagnostics– Genetically Modified Foods/Organisms Genetically Modified Foods/Organisms

(GMFs/GMOs) (GMFs/GMOs) – Gene Therapy Gene Therapy – Genetic CloningGenetic Cloning– Embryonic and Stem cell researchEmbryonic and Stem cell research– Tracing evolutionary history and linkagesTracing evolutionary history and linkages– Much, much more!Much, much more!

Applications of Genetic Applications of Genetic TechnologyTechnology

• However, all of these technologies However, all of these technologies also confront us with serious also confront us with serious potential for abuse and misuse. potential for abuse and misuse.

• The same techniques that can heal The same techniques that can heal can also be used to modify organisms can also be used to modify organisms in ways that may not be beneficial to in ways that may not be beneficial to those organismsthose organisms

• This includes the human organism This includes the human organism too!too!