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Females have two X chromosomes. And males have an X and a Y chromosome. The Y chromosome in males is shorter than an X chromosome. Because the size of the y is less than the size of the X there is less nucleotides that making up the dna of the chromosome. (A chromosome is condensed Double strand DNA)
cephalocaudal principle
The cephalocaudal principle states that development proceeds from top to bottom. According to this principle, a child will gain physical control of their head first. After this, physical control will move downward to the arms and lastly to the legs.