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.

VOCABULARY Nº18

Superposition: the idea that in a series of rock layers the bottom layer is the oldest and the top is the youngest.








Relative age: the age of a rock compared with another rock.





Geologic column: a listing of Earth's rock layers in order from oldest to youngest.








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








Index fossil: the remains of a living thing that was widespread but lived for only a short part of Earth's history.








Half-life: the time it takes for half the mass of an original element to change into a new product.





Absolute age: the age of a rock in year.





Era: one of the long stretches of time that Earth's history is divided into.