Common Misconceptions in Genetics
Tackling Myths on Traits, Cloning, Identical Twins & Cousins
Jan 31, 2009
Many areas of science are subject to misconception. Possible reasons for this include errors or sensationalizing in media reporting. Also, science is a progression, with developments people are not always aware or accepting of. For example, it was once thought that eye color was a simple trait, but this has since been shown to be incorrect.
Myth – Blue-eyed Parents Cannot Have Brown-Eyed Children
Blue-eyed parents sometimes produce brown-eyed offspring. Like many traits, eye color is not simply down to one gene. The Tech’s Understanding Genetics site have an eye color calculator that can give people an estimate of what color of eyes their child will have. They point out that this two-gene model is not always accurate, and that it’s likely other genes play a role.
Myth – Identical Twins Have Identical DNA
Identical (monozygotic) twins do share DNA, much more so than they would with other full siblings, but there are differences. Those who know twins will probably see differences between them, such as height. The current understanding of the genetics of twins suggests that environmental factors and copy number variations (CNVs) are relevant.
Genes can be switched on or off as a result of environmental factors. In the Genetic Differences Between Identical Twins article on the Eye on DNA site, author Dr Lei notes that diet and activity are examples of factors that will affect how genes are expressed.
CNVs refer to DNA regions where there are several copies of genes. In February 2008, the American Journal of Human Genetics published a paper entitled Phenotypically Concordant and Discordant Monozygotic Twins Display Different DNA Copy-Number-Variation Profiles. Authors Carl Bruder et al found differences between the CNVs of 19 sets of twins.
Myth – Clones Would Be the Same Age as the Original
In the Genetic Science Learning Centre site’s Cloning Myths article, the author points out that cloning an individual results in an embryo, not an adult double. They also acknowledge that the clone would be different for several reasons. For example, the cloned material is put into an egg cell, which will have its own mitochondrial DNA in the cytoplasm.
Cloning Myths also points out that, like identical twins, environment is also a factor. Cloning a pet cat is a good example. If the cloning was successful, the kitten would probably not behave the same way as the original cat. From day one, the kitten would be living its own life, having different experiences. Cloned kittens can also look quite different to the original cat.
Myth – The Children of First Cousins are at High Risk
Although socially unacceptable in some cultures, the genetic risks of first cousins having offspring have been overstated. Prof Bittles of the Centre for Comparative Genomics at Murdoch University reviewed 48 papers on first cousin offspring. His findings were that the risk increases from 2% (in unrelated couples) to 4% for first cousin unions. In 2002, Dr Motulsky published a review in the Journal of Genetic Counselling, with similar findings.
A doubled risk may sound dramatic, but it is not a high increase. In fact, in turning the figure round, there is a 96% chance of such a baby having no genetic health problems. However, this remains a contentious issue. Bittles suggests that first cousins concerned about having children may benefit from genetic screening.
For more information on genetics misconceptions, visit the The Tech’s Ask a Geneticist site, a genetics-themed Q & A service. Read Cool Facts on DNA and Genes for some bizarre and interesting facts on genetics.
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