Mutation is any alteration or change in DNA sequence which affects the genetic instruction carried by that gene. Mutation can occur either as a result of errors during DNA replication or due to environmental factors such as cigarette smoke and ultraviolet (UV) radiation. Mutations are heritable, especially if they have a positive effect. The disorder Down syndrome is an example of mutation which occurs due to error in cell division in which there is extra copy of a genetic material (specific chromosome); chromosome 21.
water moves through the hydrosphere in a cycle. Water collects in clouds, then falls to Earth in the form of rain or snow. This water collects in rivers, lakes and oceans. Then it evaporates into the atmosphere to start the cycle all over again
