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Genetics and the Development of the Human Brain
Chapter Five Genetics and the Development of the Human Brain
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Chapter 5 Genetics and development of the human brain
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Genotype – set of genetic instructions Phenotype – observable traits
Genetics and Behavior Genotype – set of genetic instructions 23 pairs of chromosomes made up of DNA Phenotype – observable traits Gene Expression – genetic instructions converted into a feature of a living cell Mitochondrial DNA (mDNA) originates from mother Alleles – alternative versions of particular gene
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Figure 5.1 Mitochondrial DNA Allows Researchers to Trace Population History
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Figure 5.2 Three Alleles Give Rise to Four Types of Blood
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Sources of Genetic Diversity
Genetics and Behavior From Genes to Proteins Constructed from adenine, cytosine, guanine, thymine Human gene activity in the brain very high Proteome – proteins encoded and expressed by genome Sources of Genetic Diversity Meiosis and crossing over Mutations – chromosome replication errors The Special Case of the Sex Chromosomes Sex-linked characteristics X chromosome inactivation Single Nucleotide Polymorphisms (SNPs)
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Figure 5.3 The Process of Gene Expression
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Figure 5.4 Cell Division by Meiosis
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Figure 5.5 Crossing Over Contributes to Genetic Diversity
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Figure 5.7 Probabilities of Hemophilia
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Figure 5.9 SNPs and Disease
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The Roles of Heredity and Environment
Genetics and Behavior The Roles of Heredity and Environment Heritability always refers to a population not to individuals Heritability cannot be assessed without taking the environment into account Twin and adoption studies Minnesota Study of Twins Reared Apart
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Figure 5.10 Heritability Interacts with Environment
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Figure 5.11 Similarities in Identical Twins
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Growth and Differentiation of the Nervous System
Development Growth and Differentiation of the Nervous System Early differentiation Cell germ layers – ectoderm, mesoderm, and endoderm Neural plate, neural groove, neural tube Formation of neurons and glia Originate from cells in the ventricular zone Progenitor cells divide by mitosis Cell migration Guided by radial glia Cells in cerebral cortex arrive in an inside-out fashion
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Figure 5.14 The Closing of the Neural Tube
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Figure 5.15 Neurogenesis
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Figure 5.16 Radial Glia Guide the Migration of New Cells
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Growth of Axons and Dendrites
Development Differentiation Differentiation of the dorsal and ventral halves of neural tube Differentiation of the neural tube along the rostral-caudal axis Growth of Axons and Dendrites Developing axons and dendrites end in growth cones Filapodia and lamellipodia
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Figure 5.17 Growth Cones Guide Axons to Their Targets
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Figure 5.18 Growth Cones Respond to a Variety of Cues
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Development Formation of Synapses Cell Death
Interaction with target cells influences the type of neurotransmitter released by the presynaptic cell Movement of receptors to the synaptic site guided by chemical release by presynaptic and postsynaptic structures Cell Death Apoptosis = programmed cell death Neurotrophins influence the survival of a neuron
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Figure 5.19 Steps in the Formation of a Synapse at the Neuromuscular Junction
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Figure 5.20 Growing Axons Compete for Nerve Growth Factor
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Development Synaptic Pruning Myelination
Number of functional synapses is reduced Myelination Occurs in rostral direction starting with the spinal cord, then hindbrain, midbrain, and forebrain Burst in myelination around the time of birth Prefrontal cortex not completely myelinated until early adulthood
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Figure 5.21 Synaptic Rearrangement over the Lifespan
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Effect of Experience on Development
Plasticity Experience and the Visual System Early in development cells of LGN and primary visual cortex receive input from both eyes Experience with sensory information influences segregation of ocular dominance
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Figure 5.22 Input Influences the Development of the Optic Tectum
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Figure 5.23 Input from Both Eyes Competes for the Control of Target Cells in the LGN
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Figure 5.24 Early Experiences Affect the Organization of Ocular Dominance Columns
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Effect of Experience on Development
Experience and Social Behavior Lorenz demonstrated imprinting in several species of birds Romanian children and social deprivation Ending a Critical Period Conclusion of growth spurt in myelin coincides with reduced abilities to learn additional languages Presence or absence of neurotrophins may influence timing of critical periods
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Disorders of Brain Development
Neural Tube Defects Anencephaly Spinal bifida Genetic Disorders Down syndrome Fragile-X syndrome PKU Environmental Toxins Fetal alcohol syndrome
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Redevelopment in Response to Damage
Anterograde degeneration, retrograde degeneration, and transneuronal degeneration Genetic therapy and Nogo inhibitors as possible treatments
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The Adult Nervous System
Fully mature at 25; weight of brain starts to decrease at 45 Neurogenesis in Adulthood Alzheimer’s Disease neurofibrillary tangles amyloid
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Figure 5.27 Neuronal Responses to Damage
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Figure 5.28 Alzheimer’s Disease Produces Structural Abnormalities in Neurons
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