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Child and Youth Studies
Rebecca Raby

Child and Youth Studies 
 Dr. J. McNamara Fall/Winter 2012 Lecture Overview - Biological Models of Development  Principles of hereditary transmission  How are genes expressed?  Chromosomal and genetic abnormalities  Behavioural genetics  Determining heritability  Interaction of heredity and environment: Nature and Nurture Conception  Father’s sperm + Mother’s ovum = Zygote with 46 chromosomes in total  23 from each parent Mitosis  Mitosis begins after fertilization  The process by which a cell separates chromosomes in its nucleus into two identical cells The Chromosomes  Each chromosome contains genes  Sections of chromosomes  Made up of DNA  The chemical code for development Why Not 50% mom – 50% dad? Meiosis & Crossing-Over  Chromosomes within sperm cells divide in half before they fertilize an ovum or egg cell  Chromosomes with egg cells divide in half before they are fertilized  The “splitting” is random  The randomness creates variation in the resulting embryo  This complicated process is call “Meiosis” Male or Female? rd  23 pair of chromosomes  Males have X and Y  Females have X and X  Sex of child determined by father’s sperm Male or Female? rd  Note 23 chromosome: What Do Genes Do?  Direct production of amino acids necessary for forming new cells  Guide cells to develop different parts of body  Regulate pace and timing of development  May “turn on” or “turn off” other genes  Impacted by environmental factors Gene Expression  Alleles influence many characteristics  One pair of genes  One member from mother, one from father  Simple dominant – recessive inheritance  some alleles are stronger than others  Dominant alleles (e.g. brown eyes)  Recessive alleles (e.g. nearsightedness) Gene Expression  If an allele is homozygous… (same)  Both gene are dominant or both recessive  To express a trait one must have a homozygous dominant or recessive allele  If an allele is heterozygous… (not same)  One gene is dominant and one is recessive Dominant Genes  Dominant genes are almost always stronger than recessive genes Dominant Recessive Dark hair Blond hair Curly hair Straight hair Pigmented skin Albinism Type A blood Type O blood Facial dimples No dimples Normal vision nearsightedness Chromosomal Abnormalities  How do chromosomal abnormalities occur?  Inherited congenital defects (genetic)  Mutation (spontaneous or triggered by prenatal environment)  Most abnormalities are lethal  Some are not, and some babies are born with +1 or -1 chromosome or a genetically-based disease Chromosomal Abnormalities  Sex Chromosomes  Typically females have XX and males XY  Female abnormalities  Turner syndrome: XO  Poly-X syndrome: XXX, XXXX, or XXXXX  Male abnormalities  Klinefelter’s syndrome: XXY or XXXY  Supermale syndrome: XYY, XYYY, or XYYYY Chromosomal Abnormalities  Down syndrome (trisomy 21) most common  extra 21 chromosome  Intellectual impairment (IQ < 70)  Distinctive physical features  Risk increases with age of mother (over 35 is a risk)  Can now measure for trisomy
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