Implications of Biology
• Humans have 46 chromosomes
– 44 autosomes, 2 sex chromosomes
– 23 chromosomes in a sex cell
• Egg gives an X and an X
• Sperm gives an X and a Y
– Women are usually XX
– Men are usually XY
The X and the Y
Continuums of Understanding
• Political (religious, societal, and historical)
differences “based on” Biology
• Chimp to Human is not so certain
– Chimpanzees and humans are 95%
related, in terms of common DNA
– All human chromosomes, except
the Y, first appeared (but were not
fixed) about 2,000,000 years ago—
during the time of Homo erectus,
before Humans and Neanderthals
split (600,000 years ago)
Adam and Eve
Tracing Genetic Heredity
• Gender stereotypes and their effects on
• The X chromosome develops and becomes
fixed before the Y chromosome:
• “Mitochandrial Eve” predates “Y-
– The most recent male ancestor of all males
alive today lived in Africa about 59,000 years
ago, 84,000 years after our most recent female
ancestor (143,000 years ago)
Vindija in Croatia,
which date to
and 28,000 years
ago, are more
• History paints a picture of male explorers boldly going into
new territories, expanding human horizons. Although male
adventurers have grabbed the headlines, it has been women
that have made all the running.
• According to Nature Genetics, the female migration rate has
been almost eight times that of males, over the course of
• Should the traditional picture be reversed? Should we rewrite
history in favour of Amazon adventuresses? Not quite–the
result may say more about the traditional marriage practices of
70% of human societies, in which women tend to leave home
to join their husbands' kinfolk. In this way, the genes of
women spread further, faster, than those of stay-at-home men.
6 February 2004 Health
National Wear Red
• Most commonly, test subjects are male not female, which
leads not a lack of understanding about symptoms or
warning signs—even for the same disease
– Symptoms of Heart Attack — For Women
• Feeling breathless, often without chest pain of any kind
• Flu-like symptoms - specifically nausea, clamminess or cold sweats
• Unexplained fatigue, weakness or dizziness
• Pain in the chest, upper back, shoulders, neck, or jaw
• Feelings of anxiety
– Symptoms of Heart Attack — For Men
• Sudden pressure or pain in the center of the chest
• Pain that radiates to the shoulders, neck or arms
• Dizziness, sweating, nausea or shortness or breath
• Rapid heartbeats
Genetically identical mice
Environmental/diet factors can cause physical
variations with lasting health implications
– Mother's diet can permanently alter the functioning of
genes in her offspring without changing the genes
• A strain of mouse carries a kind of trigger near the gene that
determines not only the color of its coat but also its predisposition
to obesity, diabetes, and cancer.
• When pregnant mice were fed extra vitamins and supplements, the
supplements interacted with the trigger in the fetal mice and shut
down the gene. As a result, obese yellow mothers gave birth to
standard brown baby mice that grew up lean and healthy.
• Scientists have discovered that alcohol can be
remarkably toxic—more than any other abused
drug—to developing fetuses.
– New research with imaging techniques is helping
experts uncover which parts of the developing brain are
damaged by alcohol exposure.
– Scientists are also homing in on a protein important to
the developing brain that is affected by alcohol.
• Effects of alcohol exposure seem to vary widely.
– Some fetuses seem to escape unscathed, even when
their mothers drink heavily, while others are severely
• Is the Y Chromosome Shrinking?
– Research indicates that denied the benefits of recombining
with the X, the Y recombines with itself: “The Y
chromosome has been shedding genes furiously over the
course of evolutionary time, and it is now a fraction of the
size of its partner, the X chromosome. . . . The decay of the Y
stems from the fact that it is forbidden to enjoy the principal
advantage of sex, which is, of course, for each member of a
pair of chromosomes to swap matching pieces of DNA with
– Because of technologies that allow formerly infertile couples
to reproduce, “bad” sex cells are being duplicated which
might increase infertility of their offspring; natural selection
is being altered.
• Will we move from comparing brain size to gene
numbers to determine biological superiority?
– It turns out, men have an extra brain gene that females
do not possess.
• Nobody knows what it does yet, but it is bound to attract
stereotypical jokes about parking and map-reading.
• Scientists believe that it must have played a key role in the
evolution of mankind for it to exist in the genome today.
Future: The More Things Change,
The More They Stay the Same
Sex Research Still Afflicted by Gender Stereotypes
– Dr. David Page, Whitehead Institute of MIT
• “These results show that the y chromosome is functionally
coherent; it has a short list of missions to which it is dedicated.
By contrast, other human chromosomes contain motley
assortments of genes with no theme or unifying purpose
• "The sex chromosomes represent a grand experiment of nature.
In our work, every few years we've caught a glimpse of some
unexpected aspect of this experiment. And of all these aspects,
this Y-Y gene conversion is one of the wildest."