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Chapter 3

chapter 3

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Western University
Psychology 2040A/B
Ian Mac Donald

Chapter 3: Hereditary Influences on Development -conception: zygote- 46 chromosomes, 23 from each parent -each chromosome contains genes, made up of DNA -mitosis begins after fertilization Twins: -monozygotic (identical): a zygote that divides to form two genetically identical individuals (1 in 250 births) -dizgotic (fraternal): occurs when two ova are released simultaneously and both are fertilized by different sperm (1 in 125 births) -males have X and Y -females have X and X Therefore sex of child is determined by father’s sperm 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 -alleles influence many characteristic -one pair of genes -one member from mother, one from father -simple dominant- recessive inheritance -some alleles are stronger than others -dominant vs recessive -if two alleles are homozygous: they are both dominant or recessive -if two alleles are heterozygous: one is dominant and one is recessive -if two alleles are codominant: they are each heterozygous and equal -dominant (dark hair, curly hair, pigmented skin, type A blood, facial dimples, farsightedness) -recessive (blond hair, straight hair, albinism, type O blood, no dimples, normal vision) -chromosomal abnormalities occur: -during cell division in meiosis, distribution of chromosomes may be uneven -may also occur through mutation -most abnormalities are lethal -some are not, and some babies are born with +1 or -1 chromosome -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) -autosomes: first 22 pairs of chromosomes -abrnormalities: -down syndrome (trisomy 21): ext
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