To a scientist, each puzzle piece might represent a single gene
or a portion of the DNA that makes up the space between genes.
It might seem confusing at first that people have differences in
our genes. We are all humans, and all humans must have the same
genes, right? To a certain extent, this is true. The structure and
position of each gene, like the shape and location of each puzzle
piece, is the same for essentially all people.
Individuals may have differences in the sequence of their genes
or of the DNA between genes on a chromosome, though.
Some differences produce the normal variety of characteristics we
see in a person's appearance and behavior (tall, short, fat, thin,
etc.). Other sequence differences, if within important gene regions,
can result in changes in gene expression, sometimes leading to negative
effects on a person's life. Still others may have no effect at all.
When scientists use DNA sequence to identify individuals, they pay
close attention to the subtle differences in the DNA sequence we
In addition to subtle changes, more significant DNA changes can
occur, like the deletion of a portion
or all of a chromosome. These changes can alter the expression of
many genes simultaneously and for the most part are lethal to the
individual. In the jigsaw puzzle, deletion of a whole chromosome
would be akin to deleting about two puzzle pieces.