Why is human heredity difficult to study

The goal in developing these mice was to study muscle disease and reverse the decreased muscle mass that occurs with aging. Interestingly, the Schwarzenegger mice were not the first animals of their kind; that title belongs to Belgian Blue cattle Figure 1 , an exceptional breed known for its enormous muscle mass.

These animals, which arose via selective breeding , have a mutated and nonfunctional copy of the myostatin gene , which normally controls muscular development. Without this control, the cows' muscles never stop growing Grobet et al.

In fact, Belgian Blue cattle get so large that most females of the breed cannot give natural birth, so their offspring have to be delivered by cesarean section. Schwarzenegger mice differ from these cattle in that they highlight scientists' newfound ability to induce muscle development through genetic engineering, which brings up the evident advantages for athletes. But does conferring one desirable trait create other, more harmful consequences? Are gene doping and other forms of genetic engineering something worth exploring, or should we, as a society, decide that manipulation of genes for nondisease purposes is unethical?

Genetic testing also harbors the potential for yet another scientific strategy to be applied in the area of eugenics , or the social philosophy of promoting the improvement of inherited human traits through intervention. In the past, eugenics was used to justify practices including involuntary sterilization and euthanasia.

Today, many people fear that preimplantation genetic diagnosis may be perfected and could technically be applied to select specific nondisease traits rather than eliminate severe disease, as it is currently used in implanted embryos, thus amounting to a form of eugenics. In the media, this possibility has been sensationalized and is frequently referred to as creation of so-called "designer babies," an expression that has even been included in the Oxford English Dictionary.

Although possible, this genetic technology has not yet been implemented; nonetheless, it continues to bring up many heated ethical issues. Trait selection and enhancement in embryos raises moral issues involving both individuals and society. First, does selecting for particular traits pose health risks that would not have existed otherwise? The safety of the procedures used for preimplantation genetic diagnosis is currently under investigation, and because this is a relatively new form of reproductive technology, there is by nature a lack of long-term data and adequate numbers of research subjects.

Still, one safety concern often raised involves the fact that most genes have more than one effect. For example, in the late s, scientists discovered a gene that is linked to memory Tang et al. Modifying this gene in mice greatly improved learning and memory, but it also caused increased sensitivity to pain Wei et al. Beyond questions of safety, issues of individual liberties also arise. For instance, should parents be allowed to manipulate the genes of their children to select for certain traits when the children themselves cannot give consent?

Suppose a mother and father select an embryo based on its supposed genetic predisposition to musicality, but the child grows up to dislike music. Will this alter the way the child feels about its parents, and vice versa? Finally, in terms of society, it is not feasible for everyone to have access to this type of expensive technology.

Thus, perhaps only the most privileged members of society will be able to have "designer children" that possess greater intelligence or physical attractiveness. This may create a genetic aristocracy and lead to new forms of inequality.

At present, these questions and conjectures are purely hypothetical, because the technology needed for trait selection is not yet available. In fact, such technology may be impossible, considering that most traits are complex and involve numerous genes. Still, contemplation of these and other issues related to genetic engineering is important should the ability to create genetically enhanced humans ever arise. Baoutina, A. Developing strategies for detection of gene doping.

Journal of Gene Medicine 10 , 3—20 Barton-Davis, E. Viral mediated expression of insulin-like growth factor I blocks the aging-related loss of skeletal muscle function. Proceedings of the National Academy of Sciences 95 , — Filipp, F. Is science killing sport? European Molecular Biology Organization Reports 8 , — Gordon, E. Nondisease genetic testing: Reporting of muscle SNPs shows effects on self-concept and health orientation scales.

European Journal of Human Genetics 13 , — doi Grobet, L. A deletion in the bovine myostatin gene causes the double-muscled phenotype in cattle. Nature Genetics 17 , link to article. Marteau, T. It had every chance to be lost, and yet has stood the test of time. He speculates that the ancestral gene still carries out its usual jobs in other tissues, which is why mutations in HYDIN lead to a rare disease of the lungs and airways.

Meanwhile, HYDIN2 may have taken over the brain jobs, which is why it is exceptionally active in neurons. And its origins at the very dawn of the Homo lineage, before our brains ballooned to their current large size, make this potential role that much more exciting. But if Eichler is right, HYDIN2 would join a small but growing club of genes that arose through duplications, are unique to humans, and perform important functions in the brain.

Eichler has been obsessed with duplicated genes ever since he was a graduate student in the s. In , he produced a duplication map of our DNA, a cartography of copied genes. Duplicated genes make up some 5 percent of the human genome. Many of them have arisen in the last 10 to 15 million years , since humans, chimps and gorillas started going our separate evolutionary ways.

In fact, we—the great African apes—have ended up with far more duplicated genes than, say, orangutans or macaque monkeys. No one fully understands why. For example, in other mammals like elephants, rats, and platypuses, the copies tend to sit next to the originals in a tandem series.

Genes units of heredity carry the instructions for making proteins, which direct the activities of cells and functions of the body. Genomics is a more recent term that describes the study of all of a person's genes the genome , including interactions of those genes with each other and with the person's environment. Genomics includes the scientific study of complex diseases such as heart disease, asthma, diabetes, and cancer because these diseases are typically caused more by a combination of genetic and environmental factors than by individual genes.

Genomics is offering new possibilities for therapies and treatments for some complex diseases, as well as new diagnostic methods. Genetics helps individuals and families learn about how conditions such as sickle cell anemia and cystic fibrosis are inherited in families, what screening and testing options are available, and, for some genetic conditions, what treatments are available.

Genomics is helping researchers discover why some people get sick from certain infections, environmental factors, and behaviors, while others do not. For example, there are some people who exercise their whole lives, eat a healthy diet, have regular medical checkups, and die of a heart attack at age There are also people who smoke, never exercise, eat unhealthy foods and live to be Genomics may hold the key to understanding these differences.

Apart from accidents such as falls, motor vehicle accidents or poisoning , genomic factors play a role in nine of the ten leading causes of death in the United States for example, heart disease, cancer and diabetes. See: Leading Causes of Death [cdc. All human beings are Differences in the remaining 0.

Gaining a better understanding of the interactions between genes and the environment by means of genomics is helping researchers find better ways to improve health and prevent disease, such as modifying diet and exercise plans to prevent or delay the onset of type 2 diabetes in people who carry genetic predispositions to developing this disease.

Understanding more about diseases caused by a single gene using genetics and complex diseases caused by multiple genes and environmental factors using genomics can lead to earlier diagnoses, interventions, and targeted treatments. This makes family history an important, personalized tool that can help identify many of the causative factors for conditions that also have a genetic component.

The family history can serve as the cornerstone for learning about genetic and genomic conditions in a family, and for developing individualized approaches to disease prevention, intervention, and treatment. See: My Family Health Portrait. The suffix "-ome" comes from the Greek for all , every , or complete. It was originally used in "genome," which refers to all the genes in a person or other organism. Due to the success of large-scale biology projects such as the sequencing of the human genome, the suffix "-ome" is now being used in other research contexts.

Proteomics is an example. The DNA sequence of genes carries the instructions, or code, for building proteins. In addition, each gene that acts on the trait may have multiple alleles. Environmental factors can also interact with genetic information to supply even more variation. Thus sexual reproduction is the biggest contributor to genetic variation among individuals of a species. Twentieth-century scientists came to understand that combining the ideas of genetics and natural selection could lead to enormous strides in understanding the variety of organisms that inhabit our earth.

Scientists realized that the molecular makeup of genes must include a way for genetic information to be copied efficiently. Each time cells divide to form new cells, this vast chemical library must be copied so that the daughter cells have the information required to function.

Inevitably, each time the DNA is copied, there are minute changes. Most such changes are caught and repaired immediately. However, if the alteration is not repaired the change may result in an altered protein. Altered proteins may not function normally. Genetic disorders are conditions that result when malfunctioning proteins adversely affect the organism. In very rare cases the altered protein may function better than the original or result in a trait that confers a survival advantage.

Such beneficial mutations are one source of genetic variation.