Of course there’s an element of luck in what we inherit – which we can’t control – and how our environment affects us - which we can control, up to a point. Some people will be taller than average, others smaller, just as some may be obese and smoke, and still live to be 100. Several genes have been identified associated with height variability in the normal population ( especially “ High Mobility Group “/ HMGA2 ). While very tall parents do have tall offspring, they tend not to be as tall as the parents, and vice versa ( “ regression to the mean “ ). Our genetic makeup or genotype interacts with the environment to produce our phenotype - how we look, as well as what diseases we may acquire, and there’s an important specialty of clinical genetics.
Here’s what I said in Lastlid's thread, which is now closed – please remember this is not an easy topic to explain.
We’ve come a long way since Darwin’s “ theory “ of evolution ( 1859 ), and Mendel’s experiments growing pea plants ( 1865 ). The entire human genome has been mapped in the past few years (http://www.ornl.gov/sci/techresource...ome/home.shtml. ).
Every cell has 22 pairs of chromosomes and two sex chromosomes ( XX in female and XY in male ). During the type of cell division known as meiosis, a mixture of both the individual’s parental chromosomes occurs.
If fertilization is successful, a sperm(atozoon) unites with an egg, and genetic material from the parents thus forms the unique child’s genome.
It’s complicated ! While a few traits are due to only one gene (and its alleles, or variants), most are the product of interactions between several genes. When more than one gene influences a trait, the inheritance pattern is not easily predictable. The predictable patterns referred to as dominant and recessive apply only to single gene traits. Most features are not just due to one gene, whether it’s eye colour ( http://www.burpingbaby.net/baby_eye_color.htm ), skin colour,height, or indeed how long an individual can expect to live (http://learn.genetics.utah.edu/conte...its/telomeres/ ). The same applies to diseases – which are probably all due to genetic and environmental influences. It is possible to sequence the entire genome of an individual, from a blood sample, at a price. The cost of this has steadily come down, no more than about £ 500 now – but most people wouldn’t want to do this.
Genetic tests are more likely indicated for several clinical reasons. These include carrier screening ( for breast cancer genes ), diagnosis in an individual with symptoms, testing for risk of various other cancers, pre-implantation genetic diagnosis ( embryos ), newborn screening, and forensic / identity testing. Over 1000 genetic tests are now available. Research is still ongoing - for example the Cancer Genome Project to identify genes involved in human cancer development.
