How Genetics Could Have Helped Charlie Chaplin

In 1943, actress Joan Barry gave birth to Carol Ann and claimed that Charlie Chaplin, the famous actor and director, was Ann’s father. And when Chaplin denied the claim, Barry filed a lawsuit against him demanding child support. About a year and a half later, a California Jury voted 11 to 1 in Barry’s favor. Chaplin’s appeal for the verdict was unsuccessful, and he was forced to pay child support and court fees. Was Chaplin really the father of Barry’s daughter? We don’t need to go over Chaplin’s private letters or fancy DNA testing to get an answer—we just need some basic understanding of genetics and some readily available information on Chaplin’s and Ann’s blood type. In this essay, I want to go over those things to show why Chaplin couldn’t have been Ann’s biological father.

Charlie Chaplin in The Gold Rush (1925). Courtesy: Wikipedia

Normally, most of our cells contain 23 pairs or 46 chromosomes, the tightly wound DNA strands. A sperm or an egg, however, is an exception: a sperm or an egg contains only 23 chromosomes. When a sperm fuses with an egg, the fertilized cell—called a zygote—ends up with 46 chromosomes again.  Each parent, thus, provides their child with a set of 23 chromosomes.

This means that we usually have two copies of a gene, and these copies are referred to as alleles. The DNA sequence in these alleles can be identical or slightly different (for more information on DNA sequence, read this). If the alleles are identical, the individual is homozygous for that gene but if the copes are different, then the individual is heterozygous. ‘Homo’ means the same, ‘hetero’ means different and ‘zygous’ comes from the word zygote.  

Three alleles, designated as I^A, I^B and I, create the ABO blood group system, the most common blood typing method (for more details, go here). An individual, however, can only have two of those alleles (each parent can give only one!) and should possess one of the six possible allelic combinations. Let’s take a look at those combinations and see what blood types we get from those combinations:

I^A + I^B  (Blood Type A)….....I

I^A + I     (Blood Type A)…....II

I^B + I^B  (Blood Type B)…...III

I^B + I     (Blood Type B)…...IV

I^A + I^B  (Blood Type AB)…..V

I   + I     (Blood Type O)…...VI

As we can see, different combinations of three alleles give us all the four blood types—A, B, AB or O—commonly found in the ABO system. A person will have an A blood type in both I and II scenarios, even though in the scenario I, the individual is homozygous and is heterozygous in scenario II. According to Mendelian genetics, in heterozygous animals, dominant trait always would show up in the organism, masking or hiding the recessive trait. Since in scenario II, I^A allele is sufficient to give rise to A blood type, I^A is dominant and I is recessive. Similarly, for B blood type—scenario III and IV—the dominant allele is I^B.

In scenario V, however, we see that an individual must possess both I^A and I^B alleles to have an AB blood type. Here, both traits from I^A and I^B show up! This is an exception to Mendel’s law because neither of these traits is recessive. This situation is called a co-dominance. Chaplin had an AB blood type.

In scenario VI, we see that an individual with the blood type O must be homozygous and both of his alleles must be I. Having either I^A or I^B with I, would have made that person's blood type A or B, respectively (scenario II and IV). Barry’s daughter, Carol Ann, had an O blood type.

And now, we are ready for some detective work. Chaplin carried both I^A and I^B, and he could only pass on one of those alleles to his children. His children, thus, would receive either I^A or I^B allele from him. Because Ann had O blood type, she had two I alleles. One of the I alleles had to come from Barry, and another from her father. Chaplin, however, couldn’t have given her an I allele!

Interestingly, if we reverse the situation—that is if Ann’s blood type was AB and Chaplin’s O—we still come to the same conclusion. In that case, Ann would have needed to receive either I^A or I^B from Chaplin, and Chaplin couldn’t have provided her with either. If Ann had an A or B, and Chaplin had an O blood type, however, the situation would have been more complicated because to have an A or B blood type, a person just needs one I^A or I^B allele, respectively.

The ABO blood type was discovered in the early 1900s and in 1930, Karl Landsteiner, the discoverer, received the Nobel Prize in medicine. By then, doctors started using this life-saving discovery to ensure that patients received appropriate blood type during a blood transfusion. Three doctors analyzed Chaplin’s, Barry’s and Ann’s blood when Barry sued Chaplin, and they all concluded that Chaplin couldn’t have been Ann’s father. However, at that time, blood test results were not permissible as evidence in California, so the jury had to decide the case without this key evidence. About a decade later, the law was changed so that blood test results could be used as evidence. Unfortunately for Chaplin though, the reform came just too late (you can read more about the case here).