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Lecture6_MCDB_20 - 6-15 How is sex determined in humans Sex...

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Which parent determines the sex of their baby? Why? 6-15. How is sex determined in humans? Sex chromosomes females = XX, males = XY Sex Chromosomes X Y When a sperm with an X chromosome fertilizes the egg = female baby Y chromosome = male baby Take-home message 6.15 ! In humans, the sex chromosomes carry information that directs a growing fetus to develop as a male or a female. • male if the Y chromosome is present • female if there is no Y chromosome 6.17 Down syndrome can be detected before birth : karyotypes reveal an individual’s entire chromosome set. ! karyotype • a display of an individual’s complete set of chromosomes = Useful diagnostic tool Prepared very early in the fetus’s development to assess whether there is an abnormality in the number of chromosomes or in their structure. 1. Amniocentesis By 4 months of pregnancy Amniotic fluid karyotype analysis
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2. Chorionic Villus Sampling (CVS) ! Tissue is removed from the placenta. ! Because the fetus and placenta both develop from the same fertilized egg, their cells contain the same genetic composition. ! Can be done several weeks earlier in the pregnancy, usually between the 10th and 12th weeks. Trisomy 21 or Downs Syndrome Learning disabilities, a flat facial profile, heart defects, and increased susceptibility to respiratory problems. Take-home message 6.17 ! A karyotype is a visual display of a complete set of chromosomes. ! A karyotype is a useful diagnostic tool because it can be used to identify abnormalities in a fetus’s chromosomes early in development. ! Down syndrome is caused by having an extra copy of chromosome 21. Chapter 7: Mendelian Inheritance Family resemblance: how traits are inherited Family resemblance: your mother and father contribute equally to your genetic makeup Lectures by Mark Manteuffel, St. Louis Community College How do we inherit our genes? Take-home message 7.1 ! Offspring resemble their parents because they inherit genes from their parents. ! Genes are instruction sets for biochemical, physical, and behavioral traits. 7.2 Some traits are controlled by a single gene. ! Heredity • the passing of characteristics from parent to offspring through their genes Kirk and Micheal Douglas Selective Breeding: Observing Heredity Plant and animal breeders recognize that Traits can be passed down from parent to offspring Are any human traits determined by a single gene? Traits that are determined by the instructions a person carries at one gene are called single-gene traits .
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