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Implications of Biology

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					      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

 Male                                  Female




               Any given
               characteristic
  Left                                 Right
Evolution
     Evolution Complex
• 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
                  Implications
•   Science
•   Immigration
•   Health
•   Future

• Gender stereotypes and their effects on
  scientific study
                   Science
• The X chromosome develops and becomes
  fixed before the Y chromosome:
• “Mitochandrial Eve” predates “Y-
  Chromosome Adam”
  – 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)
                      Science


Newly identified
remains from
Vindija in Croatia,
which date to
between 42,000
and 28,000 years
ago, are more
delicate than
"classic"
Neanderthals.
                     Immigration
• 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
  human history.
• 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
         Day
• 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
                                         Health
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
        themselves.
           • 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.
                        Health
• 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
     damaged.
                          Future
• 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
    its partner.”
  – 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.
                          Future
• 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
        apparent.”
      • "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."

				
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