Do your ear lobes appear to be free hanging or are they fastened securely to the side of your head? Whether or not people have attached earlobes is used to demonstrate Mendelian inheritance, but the pattern of inheritance may not be as simple as our school books suggest.
The Human Ear
In the same way that tongue rolling, widow's peak hairline, and cleft chins are thought to be perfect examples of simple dominant and recessive patterns of inheritance, so too is ear lobe attachment. As a demonstration of how Mendelian genetics work they are clear, and easy to follow examples. However, deep inside our cells the construction of a genotype may not be so simple.
Genes come in versions known as alleles. There are dominant alleles and recessive alleles and ear lobe attachment is thought to be a recessive trait. This means that;
If your father has two recessive alleles for ear lobe attachment then he will have attached ear lobes.
If your mother has one dominant allele for unattached ear lobes and a recessive allele for attached ear lobes, she will have unattached ear lobes. This is because the dominant allele always wins out.
So in this scenario what will your ear shape be?
You will inherit one recessive allele from your father, and either a recessive allele or dominant allele from your mother. If you inherit a dominant allele your ear lobes will be unattached, and if you inherit a recessive allele your ear lobes will be attached.
Ear Genetics and Complications
The first thing to say is that ear shape is not an 'either or' kind of trait. The human ear comes in a vast array of varieties, or phenotypes, and each of these will probably be governed by their own patterns of inheritance. And there maybe epigenetic factors too, which will further complicate the pattern.
Another complication is that earlobe attachment is likely to be influenced by many genes - a polygenic inheritance pattern. This idea was mooted as long ago as 1965 by Dutta and Ganguly and reinforced by Palkovich in 2006: "After nearly a century of inheritance studies, geneticists have been able to identify very few specific biological traits which are determined by a single gene. The overwhelming major of physical traits are polygenic, that is determined by the complex interactions of multiple genetic units."
The more we find out about how our genome works - i.e. the role of single nucleotide polymorphisms, 'junk' DNA having value, the role of sub-cellular, cellular, and extra-cellular environmental factors such as nutrition - the more we realise how much can sometimes be masked by over simplification. But that is not to say that the inheritance of facial characteristics is not a good starting block for understanding how genetics works.
Anne M Palkovich: Science, Race and Politics
Dutta P, Ganguly P: Further Observations on Ear Lobe Attachment. Acta genet 1965;15:77-86