The RNA bases are arranged in the same sequence as bases of the inactive strand of the DNA, except that RNA contains uracil and DNA contains thymine. There, it attaches to ribosomes, the cell's factories for manufacturing proteins. The messenger RNA instructs the ribosome as to the sequence of amino acids for constructing a specific protein. Each molecule of transfer RNA brings one amino acid to be incorporated into the growing chain of protein. A gene consists of the code required to construct one protein.
Genes vary in size, depending on the size of the protein.
The two sex chromosomes determine whether a fetus becomes male or female. The Y chromosome carries relatively few genes, one of which determines sex. In males, virtually all of the genes on the X chromosome, whether dominant or recessive, are expressed. Because a female has two X chromosomes, she has twice as many X-chromosome genes as does a male. This would seem to result in an overdose of some genes.