1. What is the Secret of Life? Deoxyribonucleic Acid is the Answer

2. History Lesson on DNA  1869  Swiss scientist Friedrich Miescher collected bloodied bandages at the local hospital  Collected nuclei from cells found on the bandages  Isolated a substance called NUCLEIN - this is the first time that DNA was isolated  Unfortunately, he didn’t know anything else about this molecule

3. History Lesson on DNA  1944  Canadian Scientist Oswald Avery proposed that DNA was involved in HEREDITY (the passing of traits down from parent to offspring)

4. History Lesson on DNA  1953  British Scientists James Watson and Francis Crick reveal the structure of DNA  Perhaps the most important scientific discovery of the century

5. Structure of DNA  Watson and Crick described the structure of DNA as a “double helix” – in simple terms, it looks like a coiled ladder  Sides of ladder – made of alternating sugars and phosphates  Rungs of ladder – made of four chemicals called nitrogen bases

6. Structure of DNA

7. Nitrogen Bases  There are only four nitrogen bases that make up a molecule of DNA  Adenine (abbreviated as A)  Cytosine (abbreviated as C)  Guanine (abbreviated as G)  Thymine (abbreviated as T)  The secret of life is contained in the order of these four nitrogen bases on a DNA molecule – GENETIC CODE  This code instructs cells what structures every cell in an organisms’ body should produce

8. The Genetic Code  The code is like a blueprint that controls the production of proteins in the cell  Proteins makes up a lot of structures in animals and plants  Airlines use three letter codes for airports around the world  YYC – Calgary  YYZ – Toronto  YVR – Vancouver  LAX – Los Angeles  Each section of DNA will code for a specific part of a protein – just like airlines

9. Nitrogen Bases  Remember that a DNA molecule is a double helix  Certain nitrogen bases are compatible only with each other  Adenine (A) will only pair with Thymine (T)  Cytosine (C) will only pair with Guanine (G)

10. How does DNA fit into the nucleus of a cell?  There is a lot of DNA in a nucleus (about 2 meters of it)  To make it fit, it is tightly coiled in little packages called CHROMOSOMES  In human cells – 46 chromosomes  Chromosomes are found in pairs (23 pairs in humans)  Offspring get one set of chromosomes from their mother and one set from their father  All cells (except for gametes) will have 46 chromosomes in their nuclei (GAMETES will have only half or 23 chromosomes)

11. Chromosomes of other Organisms  Humans have 46 chromosomes but not all species have that number  Gorilla - 48 chromosomes (24 pairs)  Fruit Fly – 8 chromosomes (4 pairs)  Sheep – 54 chromosomes (27 pairs)  Dog – 78 chromosomes (39 pairs)  Cat – 38 chromosomes (19 pairs)  Horse – 64 chromosomes (32 pairs)  Even though all of these species have different numbers of chromosomes – the DNA is still made up of A, C, G, and T – just in a different order

12. What happens when there are a different number of chromosomes in a cell?  Normal human cells have 46 chromosomes, however during reproduction, problems can occur causing fewer or more chromosomes being present

13. Down’s Syndrome  47 chromosomes – 3 copies of chromosome number 21 in humans  Mental retardation  Extra fold of skin on eyelids  A flattened forehead  Poor muscle development

14. Down’s Syndrome www.einstein-syndrome.com/ house/evan_stories.htm

15. Turner’s Syndrome  45 chromosomes – only 1 X chromosome (normal females have 2 X chromosomes and normal males have 1 X and 1 Y chromosome)  Sterile  Short stature

16. Turner’s Syndrome Karyotype of a patient with the syndrome

17. XYY “Super Male”  47 chromosomes – males that have 2 Y chromosomes (normal males only have 1 Y chromosome)  Used to be thought to be a cause of violent behaviour

18. Klinefelter’s Syndrome  47 chromosomes – males have an extra X chromosomes  Small testicles  Sterile  Frequent mental retardation

19. Genes are found on Chromosomes  Genes are segments of DNA containing coded instructions for the formation of structures  Humans have 30,000 genes on 23 pairs of chromosomes within every cell’s nucleus

20. Characteristics of Genes  Genes are located on chromosomes in nuclei  Each chromosome has a number of genes located on it  Genes, like chromosomes, come in pairs  Both genes in a pair carry DNA instructions for the same thing, and they occupy matching locations on the two chromosomes  Offspring inherit genes from both parents, however the genes may be in different forms (ALLELES)

21. Chromosomes, Genes and Alleles