start of life- genetics

start of life- genetics - Start of Life Gene.cs Prenatal...

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9/13/11 1 Start of Life: Gene.cs, Prenatal Development, and Birth Key Ques,ons What is our basic genetic endowment, and how can human development go off track? How do the environment and genetics work together to determine human characteristics? Which human characteristics are significantly influenced by heredity? What happens during the prenatal stages of development? What are the threats to the fetal environment, and what can be done about them?
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9/13/11 2 Earliest Development This first cell is created when a male reproductive cell, a sperm , pushes through the membrane of the ovum , the female reproductive cell. Gametes The sex cells from the mother and father that form a new cell at conception Zygote The new cell formed by the process of fertilization Genes and Chromosomes: The Code of Life Genes The basic unit of genetic information DNA (deoxyribonucleic acid) molecules The substance that genes are composed of that determines the nature of every cell in the body and how it will function Chromosomes Rod-shaped portions of DNA that are organized in 23 pairs Through a process called mitosis , which accounts for the replication of most types of cells, nearly all the cells of the body will contain the same 46 chromosomes as the zygote. When the sperm and ova are formed in the adult human body in a process called meiosis , each gamete receives one of the two chromosomes that make up each of the 23 pairs.
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9/13/11 3 Mul.ple Births: Two—or More— For the Gene.c Price of One Monozygotic twins Twins who are genetically identical Dizygotic twins Twins who are produced when two separate ova are fertilized by two separate sperm at roughly the same time Boy or Girl? Establishing the Sex of the Child If the sperm contributes an X chromosome when it meets an ovum (which will always contribute an X chromosome), the child will have an XX pairing on the 23rd chromosome and will be a female. If the sperm contributes a Y chromosome, the result will be an XY pairing and will be a male The Basics of Gene.cs: The Mixing and Matching of Traits We need to consider the basic mechanisms involved in the way that the genes we inherit from our parents transmit information. Dominant trait The one trait that is expressed when two competing traits are present Recessive trait A trait within an organism that is present, but is not expressed
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9/13/11 4 The Basics of Gene.cs: The Mixing and Matching of Traits Genotype The underlying combination of genetic material present (but not outwardly visible) in an organism Phenotype An observable trait; the trait that actually is seen Some of the genes form pairs called alleles , genes governing traits that may take alternate forms, such as hair or eye color.
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