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Chapter Five

Chapter Five. Genetics and the Development of the Human Brain. Chapter 5 Genetics and development of the human brain. Genetics and Behavior. Genotype – set of genetic instructions 23 pairs of chromosomes made up of DNA Phenotype – observable traits

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Chapter Five

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  1. Chapter Five Genetics and the Development of the Human Brain

  2. Chapter 5Genetics and development of the human brain

  3. 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

  4. Figure 5.1 Mitochondrial DNA Allows Researchers to Trace Population History

  5. Figure 5.2 Three Alleles Give Rise to Four Types of Blood

  6. 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)

  7. Figure 5.3 The Process of Gene Expression

  8. Figure 5.4 Cell Division by Meiosis

  9. Figure 5.5 Crossing Over Contributes to Genetic Diversity

  10. Figure 5.7 Probabilities of Hemophilia

  11. Figure 5.9 SNPs and Disease

  12. 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

  13. Figure 5.10 Heritability Interacts with Environment

  14. Figure 5.11 Similarities in Identical Twins

  15. 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

  16. Figure 5.14 The Closing of the Neural Tube

  17. Figure 5.15 Neurogenesis

  18. Figure 5.16 Radial Glia Guide the Migration of New Cells

  19. 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

  20. Figure 5.17 Growth Cones Guide Axons to Their Targets

  21. Figure 5.18 Growth Cones Respond to a Variety of Cues

  22. Development • Formation of Synapses • 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

  23. Figure 5.19 Steps in the Formation of a Synapse at the Neuromuscular Junction

  24. Figure 5.20 Growing Axons Compete for Nerve Growth Factor

  25. Development • Synaptic Pruning • 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

  26. Figure 5.21 Synaptic Rearrangement over the Lifespan

  27. 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

  28. Figure 5.22 Input Influences the Development of the Optic Tectum

  29. Figure 5.23 Input from Both Eyes Competes for the Control of Target Cells in the LGN

  30. Figure 5.24 Early Experiences Affect the Organization of Ocular Dominance Columns

  31. 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

  32. Disorders of Brain Development • Neural Tube Defects • Anencephaly • Spinal bifida • Genetic Disorders • Down syndrome • Fragile-X syndrome • PKU • Environmental Toxins • Fetal alcohol syndrome

  33. Redevelopment in Response to Damage • Anterograde degeneration, retrograde degeneration, and transneuronal degeneration • Genetic therapy and Nogo inhibitors as possible treatments

  34. 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

  35. Figure 5.27 Neuronal Responses to Damage

  36. Figure 5.28 Alzheimer’s Disease Produces Structural Abnormalities in Neurons

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