10.3 Reproductive Cloning
Reproductive cloning is a method used to make a clone or an identical copy of an entire multicellular organism. Most multicellular organisms undergo reproduction by sexual means, which involves the contribution of DNA from two individuals (parents), making it impossible to generate an identical copy or a clone of either parent. Recent advances in biotechnology have made it possible to clone mammals reproductively in the laboratory.
Natural sexual reproduction involves the union, during fertilization, of a sperm and an egg. Each of these gametes is haploid, meaning they contain one set of chromosomes in their nuclei. The resulting cell, or zygote, is then diploid and contains two sets of chromosomes. This cell divides mitotically to produce a multicellular organism. However, the union of just any two cells cannot produce a viable zygote; there are components in the cytoplasm of the egg cell that are essential for the early development of the embryo during its first few cell divisions. Without these provisions, there would be no subsequent development. Therefore, to produce a new individual, both a diploid genetic complement and an egg cytoplasm are required. The approach to producing an artificially cloned individual is to take the egg cell of one individual and remove the haploid nucleus. Then, a diploid nucleus from the body cell of a second individual, the donor, is put into the egg cell. The egg is then stimulated to divide so that development proceeds. This sounds simple, but in fact, it takes many attempts before each of the steps is completed successfully.
The first cloned agricultural animal was Dolly, a sheep born in 1996. Since Dolly, several other animals have been successfully cloned, ranging from dogs to cattle to monkeys.
Applications of Reproductive Cloning
Conservation of Endangered Species
Reproductive cloning can help preserve endangered species. In 2024, it was announced that a black-footed ferret was successfully cloned using preserved cells from a wild animal that lived decades earlier. This helps increase genetic diversity by reintroducing genetic variations that might have been lost over time. This is the first time any native endangered species has been cloned in the United States.
Agriculture
Reproductive cloning is not regularly used in livestock production, but it can be used to produce desirable animals for breeding. For example, elite animals with high milk production or superior meat quality may be cloned and used for breeding to maintain these traits in the herd.
Medical Research
Cloned animals provide uniform genetic backgrounds, which is valuable for studying diseases and developing treatments. Cloned mice may be used in medical research to study diseases and test new treatments. Their genetic uniformity allows for more controlled and reliable experiments.
De-Extinction
Cloning offers the possibility of resurrecting extinct species using preserved genetic material. Scientists are currently exploring the de-extinction of various species, including the woolly mammoth. By combining preserved mammoth DNA with the DNA of closely related Asian elephants, researchers aim to create an embryo that can be carried by an elephant surrogate.
The concept of de-extinction raises significant ethical concerns. Critics argue that efforts should focus on conserving endangered species rather than reviving extinct ones. There are also moral questions about whether humans should interfere with nature by bringing back disappeared species. Additionally, reintroducing extinct species into modern ecosystems could have unpredictable effects, potentially disrupting existing ecological balances. Despite these challenges, de-extinction has potential benefits. For instance, reintroducing the woolly mammoth might help rejuvenate tundra ecosystems and combat climate change by promoting grassland growth.
Pet Cloning
Companies offer pet cloning services, allowing owners to create genetically identical copies of their beloved animals. Pet cloning is an expensive process, and cloned pets may not always exhibit the same behaviours or personalities as their original animals. Despite the drawbacks, pet cloning is becoming more common because of emotional attachments to pets.
“10.1 Cloning and Genetic Engineering” from Biology and the Citizen by Colleen Jones is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.
