Answer:
Cold air sinks. So by heating the cold air at the bottom it is more efficient and creates an updraft and circulates the air better than if it were heated at the top.
Answer:
each cell normally contains 23 pairs of chromosomes, for a total of 46. ... Females have two copies of the X chromosome, while males have one X and one Y chromosome. The 22 autosomes are numbered by size. The other two chromosomes, X and Y, are the sex chromosomes