Red squirrels and gray squirrels have been the native species on an island for many years. A few years ago, black squirrels entered this island. The black squirrel is an invasive species. Invasive species aren’t native to the ecosystem. They move into an ecosystem because of natural changes or human intervention. Red squirrels and black squirrels have identical food requirements, but gray squirrels have a different diet. What three effects will these events have on the island’s squirrel population?

Which of the following statements is true about the relationship between genetic variation and natural selection? a. genetic variation must be present in a population before natural selection can act on it. b. genetic variation arises in a population as a result of natural selection. c. natural selection can act on a population whether there is genetic variation within the population or not. d. after natural selection acts on a population, the amount of genetic variation in the population always increases.

During crossing-over, a. genetic material is exchanged between nonsister chromatids, resulting in new combinations of alleles. b. nonsister chromatids from each homologous chromosome of a tetrad are exchanged, resulting in new combinations of alleles. c. one homologous chromosome of a tetrad is exchanged with another tetrad, resulting in new combinations of alleles. d. sister chromatids from each homologous chromosome of a tetrad are exchanged, resulting in new combinations of alleles. e. genetic material is exchanged between sister chromatids, resulting in new combinations of alleles.

As the earth formed, the force of gravity increased due to increased mass. what effect did this increased gravity have on the forming planet?