Heredity and Cell Nuclei

Building an Organism

• A plan and building materials are necessary to build a living organism, similar to building a house.
• The plan is found inside the nuclei of cells and consists of chemicals called genes.
• Genes instruct the body to make proteins, which determine the shape and behavior of the body.
• Each gene controls the production of one particular protein or a group of proteins.
• Genes are joined together to make long strands called chromosomes.
• Chromosomes and genes are made of deoxyribonucleic acid (DNA), which is a blueprint for life.

DNA and Chromosomes

• DNA is a small part of a model that shows how the body is to be built.
• Every cell in a living organism contains a copy of this plan.
• When cells divide, DNA copies itself, and a copy of this plan is passed from one generation to the next.
• This is the reason why we inherit characteristics from our parents.

Growth and Cell Division

• All living things grow from a fertilized egg-cell.
• The only way for the organism to grow is for this fertilized egg-cell to divide into two, then four, eight, sixteen cells, and so on.
• Each time a cell divides, the plans for making the organism are passed on to the new cell.
• Copies of the chromosomes and genes are made so that the plan is available in the new cells.

Mitosis

• Mitosis is the process by which a cell and its nucleus divide into two.
• The chromosomes make copies of themselves before the nucleus divides into two.
• The individual chromosomes split along their length, and a web-like structure called a spindle begins to form.
• The chromosomes arrange themselves around the equator of the spindle, and the halves of each chromosome, called chromatids, pull apart.
• The chromatids are pulled towards the two poles of the spindle, and a new nuclear membrane begins to form around each daughter nucleus.

Inherited Characteristics

• Humans inherit characteristics from both parents.
• A gene is a set of chemical instructions that controls some detail of how to build a human or a plant.
• Each gene controls the production of one particular protein or a group of proteins.