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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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