Red Hair

After the baby was born, a panicked Japanese father went to see the
obstetrician. "Doctor," he said, "I don't mind telling you, but
I'm a little upset because my daughter has red hair. She can't possibly be
mine."
"Nonsense," the doctor said. "Even though you and your wife both
have black
hair, one of your ancestors may have contributed red hair to the gene
pool."
"It isn't possible," the man insisted. "We're pure
Japanese."
"Well," said the doctor, "let me ask you this. How often do you
have sex?"
The man seemed ashamed. "I've been working very hard for the past year. We
only made love once a month."