Answer:

point mutation, change within a gene in which one base pair in the DNA sequence is altered. Point mutations are frequently the result of mistakes made during DNA replication, although modification of DNA, such as through exposure to X-rays or to ultraviolet radiation, also can induce point mutations
Answer:
(i) An allele is a variant of a gene, can either be short or tall.
Dominant = the tall allele that "trumps" the short allele. if a dominant and recessive allele is present (heterozygous) then the dominant phenotype will be shown.
(ii) David's eyes are Brown
(iii) Sarah's eyes are blue
(iv) David - B, b
Sarah - b, b
(v) Possible genotypes include Bb and bb. These give the phenotypes of brown eyes or blue eyes.
(vi) The chance for blue eyes is 50% (or 1:1 ratio)
I would guess it just means that the population just stays the same, no growth.
It can either be reflected or radiated back into space, it can get absorbed by the atmosphere, or it can reach the ground.
Good luck :)