For a human baby to be born a boy he must receive
a. an x chromosome from the father.
b. a y chromosome from the mother.
c. a y chromosome from the father.
d. both an x and a y chromosome from the father.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).

the cost of mining is extremely low compared to the money earned from mining, creating income to improve the environment.