March 25, 2013

16 of 65

Coffee

There are folks who say they can’t sleep when they drink coffee.  I am just the opposite – I can’t drink coffee when I sleep.

Actually, I don’t drink coffee any time.  My wife thinks that is very strange and suggested that I write this to explain my idiosyncrasy.  The question, then, is why don’t I like coffee.

The answer is, because it does not taste good.

I have nothing against caffeine.  I normally drink 3 or 4 cups of tea each day – because tea tastes good.

Having given the simple answer, I will take another moment to make a conjecture based on my limited knowledge of genetics.  Statistics show that more than half of Americans over the age of 18 drink coffee daily; and over 80% drink it at least occasionally.  In our family, my wife (Cathy) and our daughter (Suzanne) are coffee drinkers, while our son (Michael) and I never touch the stuff.  My first thought is that a taste for coffee may be a sex-linked trait.

Sex-linked traits are referred to as non-Mendelian inheritance patterns that are passed on through the sex chromosomes.  Most human traits are passed on through division of the somatic cells, but a few are not.  As you know, the normal female has two X chromosomes and the normal male has an X chromosome and a Y chromosome.  Though a female with an XX genotype may have a gene for a recessive trait on one chromosome, it is normally masked by the other.  However, the Y chromosome is much smaller and there is a greater chance that a gene for a recessive trait on the X chromosome of a male with the XY genotype will not be masked by the smaller Y chromosome.  Therefore, he will display that trait.

So, is a distaste for coffee the result of a sex-linked inheritance pattern?  After a bit of research, I must say, probably not.  A researcher named Linda Bartoshuk, Ph.D. at the University of Florida specializes in studying the senses of smell and taste.  She has found that the density of a person’s taste buds will affect how he or she reacts to the taste of coffee.  Those with the highest density of taste buds generally avoid the drink.  Those with a normal or low density seem to enjoy it.  (For a little more information, see http://sunburst.usd.edu/~schieber/coglab/TasteLab.html).

Her research also indicates that the density of taste buds is in fact a trait that follows Mendelian rules of inheritance.  If an offspring receives the dominant allele from both parents, which occurs about 25% of the time, he will have dense taste buds and will probably not drink coffee.  If he receives one dominant and one recessive allele, which is the case for about half of the population, his taste buds will be a little less dense and he probably will drink coffee.  The other 25% of the population has two recessive alleles.  Their taste buds are the least dense and they will tend to enjoy coffee.

I must have dense taste buds.  I don’t drink coffee because it does not taste good.