If three or more miscarriages occur in a family, unbalance should be suspected and the family's chromosomes investigated. Each parent contributes one of the vertical strands. Thousands of base pairs are needed for each gene. It is believed that the human genome has between 50,000 and 100,000 genes. DNA rearrangments Deletions in portions of a gene may occur and usually less than 20 base pairs may be involved.
Duplications are exact copies of a DNA sequence.
Substitutions involve replacement of one sequence fragment with another sequence. Insertions can occur by the movement of specific sequences and insertion into a gene. I and hemophilia. Mutations resulting from DNA rearrangements usually involve gross loss or rearrangement of many base pairs. The letters are used to depict several DNA bases.