A single gene disorder is one that's known to be caused by a single gene. Multiple gene disorders, however, can be caused by multiple gene combinations and other factors. Dominant genes are always expressed in the offspring, while recessive genes are only expressed if the offspring recieves the recessive gene from both parents. Sex-linked genetic disorders occur most often in men, and are caused by a single-gene disorder gene being on the X chromosome but not the Y, so that the offspring needs only one recessive gene to have the trait/disorder.
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The sequence of event for the evolution of the atmosphere: 1. meteorite bombardment 2. Volcanic Outgassing 3. Oceans Form 4. Banded Iron Formations Created 5. cyanobacteria evolve 6. Oxygen increases in atmosphere 7. Eukaryotes evolve
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The nervous system and the integumentary system<span />