How did some stickleback populations come to live exclusively in fresh water?
the ancestors of freshwater sticklebacks are marine stickleback species that lived primarily in the ocean and migrated to freshwater to spawn.
sticklebacks developed traits that made them better adapted to fresh water and, as a result, they moved to a freshwater environment.
stickleback populations swam to freshwater lakes to spawn and stayed because there were no predators.
some stickleback populations became trapped in lakes that formed at the end of the last ice age.

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a- all cells come from pre-existing cells

interphase

the period of cell growth when the cell synthesizes new molecules and organelles. the cell is not dividing and it constitutes the majority of the time spent in the cell cycle

prophase

changes occur in the nucleus and cytoplasm. the chromatin condenses to form structures (sister chromatids) visible with a light microscope and the mitotic spindle begins to form, but the nucleus is still in tact

prometaphase

the nuclear envelope fragments and the spindle microtubules attach to the kinetochores of the sister chromatids

metaphase

all the cell's duplicated chromosomes are lined up at an imaginary plane equidistant between the poles of the mitotic spindle

anaphase

begins when sister chromatids separate from each other and ending when a complete set of daughter chromosomes arrives at each of the two poles of the cell

telophase

the daughter nuclei form at the two poles of a cell

cytokinesis

the division of a cytoplasm to form two separate daughter cells. usually occurs during telophase during mitosis. this and mitosis make up to mitotic (m) phase of the cell cycle