Name: Amber A.
Date: March 2004
What are the possible genotypes and phenotypes for baldness?
What is the chromosome number for the gene for baldness as well as the
gene's location on the chromosome?
Answer: Many types of baldness occur, and often baldness may be a symptom
of some other illness or genetic condition or syndrome. The most common type
of baldness in healthy men has also been called "early baldness of the
ordinary type" or "male patterned baldness (MPB)" or androgenetic alopecia.
Some studies have concluded that this type of baldness is caused by an
autosomal gene situated somewhere on chromosomes 1 through 22, not on the X
or Y chromosomes. The exact chromosomal location has not yet been
identified - we don't know which chromosome, or which position on that
The gene appears to be autosomal dominant in males and autosomal recessive
in females. This means that some other gene or genes must be influencing the
way the gene is expressed.
Males who have just one copy of the gene will, of course, also have one copy
of the corresponding non-baldness gene, since all our genes occur in pairs.
In other words, these males are heterozygous for the gene. Such heterozygous
males do have baldness, according to this theory.
A female who is heterozygous, with one baldness gene and one non-baldness
gene, will not be bald. She can still pass the gene onto her sons and
daughters, but a woman will not be bald herself unless she inherits a
baldness gene from both parents. In such a case she would be homozygous for
the baldness gene.
You may wonder how it is that we do not know where this gene is on the
chromosomes, now that the Human Genome Project has been completed. The
answer is that the Human Genome Project gives us only the sequence of DNA
base pairs along the length of the chromosomes - ACGTACGT, etc. The next
challenge is to interpret these sequences and figure out which gene is
which. DNA-language is not so easy to understand even when we can read the
Please note that there are also other studies of baldness that seem to
indicate other modes of inheritance different from the inheritance pattern
described above. Perhaps we may still identify other genes that cause
baldness in certain families.
In general, it is probably easier for scientists to secure funding for
research into serious medical conditions than for research into cosmetic
situations like baldness that do not have a huge impact on people's health.
Sarina Kopinsky, MSc, H.Dip.Ed.
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Update: June 2012