Growth and Development • All living things start life as a single cell. One cell divides into 2, 2 into 4 and so on. • All living things grow and most pass through stages. • The stages an organism pass through make up a life cycle. • A life cycle starts with a fertilized egg.
Cell Division • Mitosis is the process by which most cells divide. Changes first take place in the nucleus. • Chromosomes are the threadlike structures found in the nucleus. • During mitosis a new cell gets an exact copy of chromosomes.
An inherited trait is a characteristic passed from parents to offspring. In humans, hair, eye color, skin, freckles, and the shape of our earlobes are inherited. How are characteristics inherited?
Gregor Mendel • In 1857 Mendel began experimenting with pea plants to learn how traits were inherited. • Through experimentation, Mendel learned that each parent passes one pair of its factors to an offspring. • He learned that traits can skip a generation. • He also learned that the height of pea plants depended on the factors they inherited from their parents.
Dominant & Recessive Traits • Dominant traits are strong traits. If an organism has 1 factor for a dominant trait, that trait will appear. • Recessive traits are weak traits.
Genes • A gene is the part of a chromosome that contains DNA. • A combination of about 20,000 different genes that we inherit from our parents make us unique.
Instincts • A behavior that organisms develop. • They are passed from parents to offspring. • Behaviors for building homes and caring for young are usually instinctive. • Birds know how to instinctively build their nests. • Instinctively animals know that they must hunt for food.
Learned Behaviors • Some animals instinctively know that they must hunt. They must learn how to hunt. • A learned behavior is a behavior obtained through experience. • Most behavior is learned through the teaching by adults of the same species.
Environmental Influences • Some behaviors and characteristics are a result of environmental influences. • All living and nonliving things that affect an organism make up its environment. • Changes in the environment can cause animals to change their behaviors.
Questions • How does cell division affect growth? • What characteristics are inherited? • What other factors affect characteristics?