Ask A Scientist© Biology Archive

 
Question:  Why can frogs (some species) change sex?
Mike A Smola

Answer:
This is a complex subject.  Several studies have exposed some of
the answers to this question, but a definitive answer is yet to be
made.

It all boils down to the level of which genes are activated.
Studies have shown that the sex chromosomes are not necessarily the
determining factor.  The traditional display of a female is when
an individual has two X chromosomes present.  When one of these
genes is a Y, it is a male.  This tends to be the case for most
organisms that sport individuals that are different sexes.
However, the Y chromosomes has been almost always a male determining
chromosome, but with molecular biology and genetic engineering
techniques, a male can be made from a XX combination and females
have developed from XY combinations.  These are extremely rare, but
they have given insight to the fact that there are other factors
beside X and Y chromosomes that determine sex, probably a gene
found in both chromosomes.
 
As far as frogs are concerned (and other organisms that display this
Phenomenon), apparently there are chemical triggers that respond to the
number of members in a population that will activate the gene(s)
that will allow for the disintegration of one set of sex organs and
the development of the other.  This is an advantage to a species
whereby they have evolved the ability to assure their reproductive
success.
Steven D Sample