People save money in banks, in case of an emergency. Genetic banks serve a similar purpose for farmers and scientists who work to conserve rare plants and animals. Researchers or farmers can withdraw samples from these “gene” banks to help rebuild populations of rare plant varieties and animal breeds or to help increase genetic diversity within species.
Gene banks also preserve cells or organisms that host unusual gene variants — genes with special traits. Those genes might later prove useful when some disease epidemic strikes, when the climate changes or when other factors threaten the survival of plants or animals. Farmers could use the banked deposits — stored cells or tissues — to restore genetic diversity or to introduce traits from other breeds or varieties.
Some gene banks house millions or even billions of plant seeds. One example: the Svalbard Global Seed Vault. It’s located underground on a remote island north of Norway. The San Diego Institute for Conservation Research houses another project, called the Frozen Zoo. Its collection includes cells from thousands of birds, reptiles, mammals, amphibians and fish. The cells stored there might one day be used to help rebuild populations of endangered species.
The Smithsonian and SVF Biodiversity Preservation Project in the United States freezes semen and embryos from rare breeds of domestic animals. The U.S. Department of Agriculture’s Agricultural Research Service (ARS) has an even bigger program. It has almost a million samples of semen, blood and embryos from both common and rare breeds. Such collections serve “as a backup to the United States’ livestock industry,” explains Harvey Blackburn. He’s an animal geneticist. He also manages the National Animal Germplasm Preservation Program at an ARS lab in Fort Collins, Colo.
Gene banks use low temperatures to stop chemical and biological activity that might break down cells. Some banks freeze material in liquid nitrogen at –196° Celsius (-320.8° Fahrenheit). This freezing process replaces water in cells with another fluid, such as glycerol. That fluid minimizes the development of ice crystals. Such crystals could damage cell walls. Later, during thawing, biologists will remove the glycerol or some other fluid and return water to the cells.
Freezing and thawing cells has to be done quickly and carefully so that the material will still be viable after it has warmed back up. But some material requires extra special care.
The sperm from chickens and other poultry, for instance, do not survive the freezing and thawing cycle as well as does the sperm from cows and other mammals. Bird biology partially explains why, says Julie Long. A physiologist, she studies animal reproduction at an ARS lab in Beltsville, Md. Unlike female mammals, hens store sperm for several weeks after a single mating. Then they use those sperm over time to fertilize eggs. So thawed sperm must be very hardy to last such a long while in the female bird’s reproductive tract, she explains.
The shape of the frozen material also can affect how well it survives freezing. Bird sperm looks like a piece of string. That shape makes it more fragile than the sperm of most mammals, which contain a round head and slender tail. Ice crystals can more quickly damage DNA in a bird’s sperm.
But Long and other researchers are working to make the sperm of birds more resilient. “Bird sperm seems to respond better to a very fast freeze,” such as a 200 °C drop in one minute, notes Long. That’s more than three times as fast as the freeze rate necessary to preserve the sperm of mammals.