Genetics, DNA, and Heredity

What is DNA?

DNA - DeoxyriboNucleic Acid

Long molecule used in storing hereditary (genetic) information makes up genes.

- “blueprints” that build an organism.

Gene

Gene – small piece (segment) of DNA that codes for a specific trait.

- Trait - eye color, hair color, height, etc.

Where are Genes?

Genes pass on hereditary material to offspring.

Asexual reproduction – all genes come from one parent (mitosis).

- Offspring identical to parent.

Sexual reproduction – half genes from mom and half from dad (meiosis).

- Offspring are different from parent.

Structure of DNA

DNA is made up of thousands of smaller molecules called nitrogenous bases.

a. Adenine (A)b. Guanine (G)c. Cytosine (C)d. Thymine (T)

These 4 bases exist in pairs:Guanine-Cytosine (G-C) and Adenine-Thymine (A-T)

(Good Couples are Always Together)

4 Kinds of Nitrogenous Bases

Shape of DNA

Double Helix – looks like a twisted

ladder with two strands of DNA wrapped

around each other.

The “Ladder” (Draw Me!)Nitrogenous bases form the “steps” of the ladder

“Packaging” DNA

The nucleus contains the chromosomes.

Chromosomes contain lots of DNA strands which make up genes.

DNA Replication

Before a cell divides (mitosis or meiosis) it must replicate, or copy, its DNA.

- This makes sure that all cells have copies of the DNA.

How is DNA Replicated?

DNA is replicated in 3 steps: Original DNA molecule unzips 2 new strands begin to take form Two identical DNA strands are formed

1. Unzip original DNA

Original DNA molecule becomes separated (unzips).

2. Expand Two New Strands

Each original strand now becomes a template (model) for a new strand of DNA.

Base pairs are added to new strand using the same rules Good Couples Always Together.

Original

A

T

T

G

New

T

A

A

C

New Strand

3. Two Identical DNA Molecules are Formed

Two new DNA molecules formed, each with 1 original strand and 1 new strand.

Heredity and Traits

Proteins decide which traits will be shown by the offspring.

DNA codes for which amino acids will make the proteins.

What Organelle Makes Proteins?

The organelles that assemble proteins from amino acids are the ribosomes.

How Does DNA’s Directions Get to the Ribosomes?

1. A messenger molecule (RNA) copies information from the DNA.

2. The messenger molecule (RNA) goes to the ribosome.

3. The ribosome collects amino acids and assembles the proteins in the proper order.

Changes in Heredity- Mutations

Nothing is perfect…

Mutation – any changes (alterations) in the sequence of DNA that affects genetic information and the appearance of offspring.

Types of Mutations

Gene mutation – a mutation that occurs in a single gene and affects one trait.

Ex: Eye color, Sickle cell Anemia, Hemophilia

Chromosome mutation – a mutation that occurs in many genes and affects many traits at once.

Ex: Down Syndrome (an extra 21st chromosome)

How Can Mutations Affect an Organism?

Body cell mutations can cause cancer.

- only the individual is affected.

Gamete cell mutations affect the egg and the sperm.

- all offspring of the individual can be affected.