GPS Standard

• S7L3 Students will recognize how biological traits are passed on to successive generations.

• a. Explain the role of genes and chromosomes in the process of inheriting a specific trait.

DNA

• Deoxyribonucleic acid is also known as DNA.

DNA

• DNA is the genetic material that determines inherited characteristics.

• DNA is made up of units called nucleotides. • A nucleotide consists of a sugar, a phosphate

and a base.• The four bases are adenine, thymine, guanine,

and cytosine.

Nucleotides

Nucleotides

• Each base is referred to by their first letter. A, T, C, and G.

• Each base has a different shape. They fit together like the pieces of a puzzle.

• In the 1950’s a biochemist named Chargaff discovered the amount of Adenine (A) always equals the amount of Thymine (T). And the amount of Guanine (G) always equals the amount of Cytosine (C). This is known as Chargaff’s Rules.

The Discovery of the Structure of DNA

• Rosalind Franklin a chemist from Britain used X-Ray diffraction to process the image of DNA.

• It suggested that DNA has a spiral shape.

The Discovery of the Structure of DNA

• At about the same time 2 scientists, Watson and Crick, were also trying to solve the mystery of DNA’s structure.

• Using the information of Chargaff and Franklin they concluded that DNA must look like a long, twisted ladder. They developed a model that eventually helped explain how DNA is copied and how it functions in the cell.

Watson and Crick

DNA

• DNA looks like a twisted ladder. It is also known as a Double Helix.

• The sides of the ladder are made of alternating sugar and phosphate parts.

• The rungs of the ladder are made of a pair of bases. Adenine (A) always pairs with Thymine (T). Guanine (G) always pairs with Cytosine (C).

Making a copy of itself

• During Replication DNA makes a copy of itself. It splits down the middle and a complimentary strand is created.

• DNA is copied every time a cell divides. Each new cell gets a complete copy of all the DNA.

Heredity

• Heredity – the passing of genetic traits from parent to offspring.

• Gene – one set of instructions for an inherited trait.

• Trait – a genetically determined characteristic

Changes in Genes

• Changes in the number, type, or order of bases on a piece of DNA are known as mutations.

• Deletion – when a base is left out• Insertion – when a base is added• Substitution – when a wrong base is used

Changes in DNA

• There are 3 possible consequences to changes in DNA. An improved trait, no change, or a harmful trait. Fortunately, cells make proteins that can detect errors in DNA. When an error is found it is usually corrected. Sometimes the mistakes become part of the genetic message. If this happens in the sex cells it can be passed from one generation to the next.

Changes in DNA

• Sometimes damage to DNA can be caused by abnormal things that happen to cells. A physical or chemical agent can cause a mutation in DNA. Examples are high-energy radiation from X rays and ultraviolet radiation (a type of energy in sunlight). Other examples are asbestos and the chemicals in cigarette smoke.

An example of Substitution

• This can be harmful because it may cause a gene to produce the wrong protein.

• Creating the wrong protein can cause the disease sickle cell disease which affects red blood cells.