A baby typically inherits DNA from two parents. However, advancements in reproductive science allow a child to receive genetic contributions from more than two individuals. This unique situation arises through specific medical procedures designed to prevent serious inherited conditions. In these cases, a baby can indeed have DNA from two mothers, alongside DNA from one father.
The Two Types of Human DNA
The human body contains two distinct types of DNA: nuclear DNA and mitochondrial DNA (mtDNA). Nuclear DNA resides within the nucleus of nearly every cell. This genetic blueprint, comprising approximately 20,000 to 25,000 genes, determines an individual’s unique traits, such as eye color, hair texture, height, personality, and intelligence. Nuclear DNA is inherited equally from both biological parents.
In contrast, mitochondrial DNA (mtDNA) is a smaller genetic component found outside the nucleus, within organelles called mitochondria. Mitochondria generate energy for cellular processes. Unlike nuclear DNA, mitochondrial DNA is inherited exclusively from the mother. This maternal inheritance occurs because sperm contribute very few mitochondria to the egg during fertilization.
Why Mitochondrial DNA Donation is Needed
Mitochondrial DNA donation procedures address inherited mitochondrial diseases. These are a group of inherited disorders that occur when mitochondria fail to produce enough energy for the body’s cells to function properly. Since mitochondria are present in nearly all cell types, these diseases can affect various organs and systems, leading to debilitating symptoms. Symptoms can include muscle weakness, neurological problems, heart conditions, liver disease, and developmental delays.
A mother carrying faulty mitochondrial DNA has a high risk of transmitting the disease to all her children. Mitochondrial donation offers a way for mothers at risk of passing on severe mitochondrial diseases to have a genetically related child free from these debilitating conditions. This intervention aims to prevent these diseases.
How Mitochondrial Donation Procedures Work
Mitochondrial donation involves in vitro fertilization (IVF) techniques that combine genetic material from three individuals. The two primary methods are Maternal Spindle Transfer (MST) and Pronuclear Transfer (PNT). Both procedures aim to replace the mother’s faulty mitochondria with healthy ones from a donor egg while retaining the nuclear DNA from the intended parents.
In Maternal Spindle Transfer, the nucleus is removed from the mother’s egg. Simultaneously, the nucleus is also removed from a healthy donor egg, leaving behind its healthy mitochondria and other cellular components. The mother’s nucleus is then transferred into the enucleated donor egg. This reconstructed egg, containing the mother’s nuclear DNA and the donor’s mitochondria, is then fertilized with the father’s sperm in a laboratory setting.
Pronuclear Transfer is performed after fertilization. In this method, eggs from both the biological mother and a healthy donor are first fertilized with the father’s sperm. After fertilization, two pronuclei form within each egg, one from the egg and one from the sperm.
The pronuclei from the biological mother and father are then removed from their zygote. These pronuclei are transferred into the donor zygote, which has had its own pronuclei removed, leaving its mitochondria. The resulting embryo, with nuclear DNA from the intended parents and donor mitochondria, is then transferred into the biological mother’s uterus.
What It Means for the Child
For a child born through mitochondrial donation, the vast majority of their genetic makeup, over 99.9%, comes from the nuclear DNA of their parents. This means that all the characteristics that make a person unique, such as their appearance, personality traits, and inherent talents, are determined by their parents’ genetic contributions. The child will resemble their parents and share their family’s genetic heritage.
The contribution from the mitochondrial DNA donor is less than 0.1% of the child’s total DNA. This DNA provides the mitochondria necessary for cellular energy production. It does not influence the child’s physical traits, intellectual abilities, or identity. The mitochondrial donor contributes a cellular component that ensures proper cell function, preventing severe mitochondrial disease.
Ethical and Regulatory Landscape
The development of mitochondrial donation techniques has sparked ethical and societal debate. Discussions often center on concerns about altering the human germline, creating “designer babies,” and the welfare of children born through these procedures. Proponents highlight the benefit of enabling families to have healthy, genetically related children free from devastating diseases. They argue that the limited genetic contribution from the donor means the procedure is more akin to a cellular transplant than a significant alteration of identity.
Due to these considerations, the regulatory landscape for mitochondrial donation varies across countries. The United Kingdom was the first country to legally permit mitochondrial donation in 2015, following public consultation and scientific review. This regulatory framework allows for the clinical use of these techniques under strict oversight. Many other countries have either explicitly banned these procedures or have not yet established specific regulations, effectively making them unpermitted in practice. Ongoing scientific advancements and evolving ethical discussions continue to shape global perspectives on this technology.