Minor errors or early injuries can be compensated for

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Minor errors or early injuries can be compensated for. If not needed, these neurons/synapses undergo programmed destruction.
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Mylenation Schwann cells (glia cells) produce myelin Mitotic Schwann cell progenitors travel along axon → become immature Schwann cell October 19, 2012: Development of the Nervous System II Behavioral Development and Plasticity: Genotype, Environment, and G x E Interaction What is the proximate basis by which genetic and environmental factors influence phenotypes? Environmental factors interact with genotype in complex ways during development to produce the adult phenotype The “environment” includes all non-genetic factors experienced by an organism, including those within the womb or egg before birth. Environmental effects on development: hypoxia malnutrition maternal drug use Genetic effects on development chromosomal problems genetic variation in populations Case Study: Impulsivity Self-control/impulsivity Self-control develops slowly in humans, possibly due to prolonged prefrontal cortex development. Important societal consequences Can be measured in the lab. We know some genetic and some environmental correlates of the development of impulsivity, including: parenting quality lead exposure dopamine receptor alleles serotonin transporter alleles Genes and environment may act largely independently or may interact in complex ways ( gene x environment or GxE interaction ) has at least one 7-repeat allele AND low parenting quality = more impulsive Take-Home Relationships between genetics, environmental variation, and phenotypes is incredibly complex. Development is generally most plastic early in life, while it is proceeding rapidly, so understanding genetic and environmental effects is important at that stage for drug treatments, behavioral therapies, etc. Evolutionary Developmental Biology (Evo-devo) of the Nervous System What is Evo-devo? It is a modern field Integrates evolutionary (ultimate) and developmental (proximate) explanations for how phenotypes arise. Example: how can brain size or organization change over evolutionary time? Evo-devo hypothesis? Selection affects genes that regulate how long progenitor cells divide symmetrically – i.e. more cortical divisions in humans than rats. Case study: Eye Patterning What determines how body axis polarity is established? Where limbs grow? How color patterns are generated? Patterning genes are expressed at different levels in different parts of the organism Hox genes are the most well-known patterning genes
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regulate anterio-posterior patterning Are vertebrate and cephalopod eyes homologous or examples of convergent evolution? In addition to Pax6 (hox gene used in eye development), molecules that detect light are shared b all animals, indication a common evolutionary origin (homology) Convergence in animal eyes Cephalopods: successive infolding of the exterior body wall.
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