Chapter 7 Lesson 1 COPY ENTIRE SLIDE A

Chapter 7

Lesson 1

(COPY ENTIRE SLIDE) �A trait is a distinguishing characteristic of an organism. � During reproduction, traits are passed down from one generation to the next, this is known as inheritance. � For every organism there is a range of inherited traits. � Hair color � Eye color � Petal color � Attached ear lobes Can you name more?

(COPY ENTIRE SLIDE) � Not all traits are inherited. � An acquired trait is a trait that an organism acquires or develops during his lifetime. �Loosing a limb (arm/leg) �Learning a trick/sport �Neat handwriting �Growing long hair Can you name more?

� Organisms pass traits to their offspring in one of the two ways: � Asexual reproduction – it produces offspring who are identical to the original; passing of traits by cell division an mitosis �Example: amoebas, bacteria, and some plants � Sexual reproduction – produces offspring that are similar but not identical to the parent or parents; requires DNA from both reproductive cells �Example: humans, most species

DNA appears as a twisted zipper in the nucleus; when stretched out can be almost 2 meters long! It can fit into a cells nucleus since it is tightly coiled with proteins to form chromosomes. � DNA – (Deoxyribonucleic Acid) contains genes � Genes – a section of DNA that has genetic information for one trait � Genes carry instructions for traits.

� Chromosomes are found in the nucleus and carry long pieces of DNA. � The number of chromosomes differs depending on the species and in most species they come in pairs. � Humans have 23 pairs of chromosomes in each body cell. � Each pair contains one chromosome from the father and one from the mother. � Reproductive cells are known as the sperm and egg; each contains 23 single chromosomes. Within each chromosomes lies hundreds or thousands of genes.

Much of this randomness is due to meiosis. � During meiosis, new sperm cells and egg cells form when the chromosomes in existing cells replicate and divide. � The number of chromosomes is reduced by half 23 chromosomes � One reproductive cell (with replicated chromosomes) will split into 4 separate cells, each containing a unique combination of genes. �

� Occurs when egg cell and sperm cell combine to form an offspring with a full set of paired chromosomes. � Resulting in unique offspring. � There are many potential gene arrangements when chromosomes combine in humans. � A mother and father could have billions of offspring and no two would be alike.

� During reproduction an egg cell and a sperm cells each contribute one gene for a trait. � Each gene for a single trait is called an allele. � Traits are expressed in the offspring by chance.

� Dominant Allele – one whose trait shows up in an organism when an allele is present; represented by a capital letter � Recessive Allele – a trait that is hidden whenever a dominant allele is present; represented by a lowercase letter � Homozygous – an organism that has two identical alleles for a trailt � Heterozygous – an organism that has two different alleles for a trait

… is used to predict the possible outcomes of offspring.

�Genotype – an organisms complete set of genes; once inherited it remains unchanged. �An organisms environment can influence traits expressed by the genotype. �Phenotype – how a trait appears or expressed �Environmental Factors, such as physical and social factors, are not constant and can alter an organisms phenotype.

� Light is a physical factor. �Example: Plants need light. Plants that grow tall in full sunlight, might not grow as tall in low light. � Nutrients can also affect trait expression. �Examples: Low levels of nitrogen or iron in the soil may turn a plants leaves yellow or cause them to fall off. Flamingos are born white, but turn pink because of the food they eat (algae and crustaceans) are rich in red pigment. � Moisture and Temperature also physical factors.

� An organisms social group can also affect color, body structure, or behavior. �Examples: Locusts are usually solitary individuals and are a green color. When locusts are in large groups they apply pressure on each others legs, causing them to change color to yellowish-brown and swarm. Flamingos live in large social groups. A flock consisting of at least 20 is needed for breeding to occur in zoos. Adding more birds to a flock increases breeding success. In the wild these birds will live in flocks of 10, 000.