Name:______________________________________
February________, 2012
Chapter 20 – The Role of Genes in Inheritance
Section 1 – Continuing Life
A. Hereditary material is passed from parent to offspring during reproduction.
1. DNA - a chemical that contains hereditary information that controls how an organism
functions and looks. DNA is shaped like a twisted ladder.
2. The secret of DNA has to do with the sequence or order of bases along the ladder.
3. Mitosis is the process of cell division that results in two nuclei, each with the same
genetic information or DNA.
B. Asexual Reproduction - reproduction in which a new organism is produced from a part of
another organism by cell division.
1. Single celled organisms, like bacteria, divide or split in half to reproduce.
2. Budding is a type of asexual reproduction where a new organism grows on an older one.
The new organism is identical to the older one.
3. In a process called regeneration, some organisms are able to replace and repair lost or
damaged body parts.
4. Cloning - making an exact copy of an organism.
C. Sexual Reproduction - a type of reproduction in which a new organism is produced from
the DNA of two sex cells (sperm and egg).
1. Sex cells form by Meiosis - a double cell division process that result in four new cells each
with half the number of chromosomes of the original cell.
2. Human sperm and egg each contain 23 chromosomes each.
3. When fertilization occurs each sex cell contributes half of the chromosomes.
4. The new individual will have a set of 46 chromosomes.