A woman with brown eyes, which has two brothers, marries a man with brown eyes, which has a brother and two sisters, and produces a boy with brown eyes. When their son marries a woman with blue eyes, they have a girl with blue eyes. All of the boy's aunts and uncles have brown eyes, as do his grandparents. However, his mother, the little girl's grandmother, has an uncle with blue eyes. Trace the family history of eye color and determine how the little girl could have blue eyes.

ionic bonds are two oppositely charged ions that attract. a sodium ion has a 1 positive charge; a chloride ion has a 1 negative charge. sodium and chloride have oppostive charged ions that attract which forms an ionic bond. a chemical bond formed when two atoms share electrons is called

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the oldest known insects are believed to live around 400 millions ago as suggested by the fossil records.   some plants having woody stems also evolved during this time.

after the evolution of insects the first four legged species or the tetrapods evolved in shallow freshwater habitats from the intermediate species approximately 397 million years ago. the tetrapods went on conquering the land giving rise to amphibians, reptiles, mammals and birds.

the major split in tetrapods first occurred 340 million years ago branching off from amphibians.

363 million years ago when the carboniferous period began the insects started roaming on land and taking flights, following which the four limbed tetrapods adapted in the terrestrial habitat.