Last Flight of Bomber 31

Answer to to identify which members of a family share the same mitochondrial DNA (mtDNA).

Everyone carries two types of DNA: nuclear DNA, found in the nucleus of each body cell, and mitochondrial DNA (mtDNA), found in the mitochondria located in the cell's cytoplasm outside the nucleus. Nuclear DNA codes for most proteins made by the cell and is responsible for the inheritance of physical traits, such as hair color or whether a person has dimples, as well as inherited genetic disorders, such as sickle cell anemia or Tay-Sachs disease. MtDNA codes for its own proteins and for ribosomal and transfer RNAs.

During reproduction, the father's sperm cell -- which contains both nuclear DNA and mtDNA -- donates only its nuclear DNA to the zygote that results from the fusion of the sperm with an egg cell. (Some researchers argue that a fragment of the father's mtDNA is in fact passed on, though it represents much less than 1 percent of the total.) Therefore, all the DNA in a person's mitochondria comes from his or her mother. This means that each new generation has only the mtDNA of the mother, who has only the mtDNA of her mother, and so on. (Males have only the mtDNA of their mothers as well but do not pass it on.) As a result, mtDNA samples can be used to identify any maternally related individuals.

The people related to the missing person's maternal grandmother (who are the candidates for getting mtDNA to compare to that of the missing person), are connected with heavy lines in the pedigree chart below. The 10 living relatives eligible for testing are shaded.

Who's Related by mtDNA?
Answer chart

MtDNA could be used to confirm that two brothers with the same mother who died in a crash were related, but not used to distinguish their remains from one another in the way that nuclear DNA could. Because mtDNA molecules are present in thousands of copies per cell (compared to nuclear DNA, which is present in only two copies per cell), mtDNA is more likely to be found in small or degraded samples than is nuclear DNA. In addition, environmental factors, such as prolonged exposure to the elements, often destroy nuclear DNA.