Name: Fauzia Khan
Date: April 2003
What is the difference between autosomes and sex
chromosome and thier functions?
Autosomes are any chromosomes other than the sex chromosomes. They serve no special function
except that they each contain different genetic instruction. The sex chromosomes are
distinguished from the others because one gene on the Y( that activates another set of genes) is
the SRY, or sex-determining region of the Y, gene. When this gene turns on it begins the male
pattern of development. So far, the going information is that if there is no SRY to turn on,
the "default" pattern the embryo becomes female. Some scientists are skeptical of this,
however, and are searching for a "sex-determining" gene in females, perhaps on the X. Even
though the X doesn't contain a sex determining gene (that we know of!), it pairs with the Y
during meiosis and they do exchange a small amount of information during crossing over. The
combination of the two chromosomes determines sex of the offspring in humans.
Interesting question and far more complex than it might seem. Aside from
the sex chromosomes producing certain proteins that obviously affect sexual
development (i.e., the sry gene on the Y chromosome) the "sex
chromosomes"...especially the X chromosome have genes for all sorts of
functions as do the autosomes. The Y chromosome (about 59 million bases) is
a little different because it is so small ( chromosome #1 has 263 million
bases!). The Y has very few genes...the sry and some genes for sperm
production and what some seem to think is a lot of junk. The X chromosome
is much larger than the Y at 164 million bases. There are entire books
written on this subject and anywhere near a comprehensive understanding of
the interaction of proteins produced by the genes of different chromosomes
is many decades away...and might not even be possible...something like what
I call incomprehensible complexity. The X, by the way, has a gene involved
with prostate cancer.
The autosomes are the general chromosomes that carry the information to make a human being.
They all come in pairs (one set from mom, one set from dad).
The sex chromosomes also come in pairs, but come in two types -- X and Y. In humans, the Y
chromosome carries the information for a few hormones and receptors that make an XY embryo
develop male characteristics. An XX embryo lacks the "testis determining factor" and develops
The process is further complicated because the female carries 2 X chromosomes while the male
has only 1. So in mammals, one of the two X chromosomes in females gets inactivated. This is
why calico cats are virtually always female - one X chromosome carries the gold color and the
other X chromosome carries the black color. If the gold chromosome is shut off, the fur is
black. If the black is shut off, the fur is gold. A male could carry either the black or the
gold chromosome, but not both since he's XY. So in males, no chromosome gets shut off.
Christine Ticknor, Ph.D.
Ireland Cancer Center
Case Western Reserve University
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