The plus sign is going to illustrate the dominance
piece of the puzzle.
Sex determination in humans, you are probably
all fairly familiar with the female has a
possibility of contributing X and X and the
male could contribute and X or a Y. And the Y
chromosome is a little bit special. First
of all, it is tiny, but it also has a gene
on it that is involved in sex determination.
It is called the SRY region of the Y chromosomes.
It is the sex-determining region of the Y
chromosome. And if that gene is present and
expressed, then we will see maleness, but
if that gene is not present maybe there is
no Y chromosome or maybe the gene is broken,
then by default we will see the female phenotype
in human condition. We know how this works
out. We have an X and a Y. We can have male
progeny or X is in excess, we have female
progeny. Fifty percent chance of boys or girls
based on this sex determining system. We will
see also in other species that there are different
mechanisms going on for sex determination
although there are sex determining chromosomes.
The humans we have X and Y and the birds,
we will see as ZW system. The other thing
with birds as we see that the homozygous form
is the male form. ZZ make birds male and ZW
makes birds female. We can also see that in
grasshoppers, there is a different situation
in which grasshoppers have an XX or an XO. The
O means that there is nothing there. It just
has one chromosome involved in sex determination
whereas honeybees use different systems still.
The female is diploid whereas the male is
a haploid organism, whole other set of chromosomes
to become female. That brings us to a little
bit of a question and thinking about things