VOCABULARY Nº25

Neuron: an individual nerve cell.

Dendrite: a nerve fiber that carries messages toward the cell body.

Axon: a nerve fiber that carries messages away from the cell body.

Synapse: the gap between neurons.

Sensory neuron: a nerve cell that picks up stimuli and sends impulse produced by the stimuli to the brain and spinal cord.

Stimulus: anything that causes a response.

Motor neuron: a nerve cell that carries commands from the brain and spinal cord to the muscle and glands.

Associative neuron: a nerve cell that passes impulse from sensory to the motor neurons.

VOCABULARY Nº24

Variation: the difference in appearance of an inherited trait in the members of a species.








Adaptation: a variation that increases an organism's chances for survival.









Natural selection: a theory that says organism's best adapted to their environment live longest and pass their traits to their offspring.








Competition: the struggle among living things to obtain the resources they need to survive.





Mutation: a change in a gene.





Isolation: the separation of one group from others of the same species

VOCABULARY Nº23

Fossil: any remains, trace, or imprint of a living thing preserved in Earth's crust.








Extinct: died out (referring to an entire species).





Evolution: the theory that species changes over time, resulting in new species.

VOCABULARY Nº22

X and Y chromosomes: chromosomes that determine a person's sex.








Sex-linked gene: a gene carried on an X chromosome but not a Y chromosome.








Selective breeding: the process of crossing plant or animals to produce offspring with certain desirable traits.








Genetic engineering: a way of changing the DNA sequence in a gene so that the gene will produce a particular trait.








Gene-splicing: attaching the genes from one organism to the genes in another organism. 

VOCABULARY Nº20

Probability: how likely it is for something to happen.








Punnett square: a table for predicting the outcome of crossing different forms of a trait.





Pedigree: a chart used to trace the history of trait in a family.





Carrier: an individual who has inherited a factor for a trait but does not show the trait.





Incomplete dominance: a genetic pattern in which neither of the two forms of a trait completely masks the other.

VOCABULARY Nº19

Inherited trait: a characteristic that is passed form parent to offspring.








Heredity: the passing of inherited traits from parents to offspring.





Genetics: the study of how heredity works.








Pollination: the transfer of pollen from the male part to the female part of the plant.








Hybrid: an organism produced by the crossing of parent that have different forms of the same trait.








Dominant trait: a form of a trait that appears in the hybrid generation.








Recessive trait: a form of a trait that is hidden, or masked, in the hybrid generation.