PSYB64 midterm 2

• only 10-20% of the genes in any particular type of cell are active
• epigenetics: changes in phenotype produced solely by changes in expression, not the genotype itself
• epigenetics are not from a DNA sequence change but could be from environments
• two processes determine gene expression: DNA methylation and histone modification
• gene expression cause by DNA methylation is when abnormal methylation leads to disease
• gene expression cause by histone modification is when epigenetic tags interact with histones to alter gene expression
• maltreated children showed increased methylation in low methylation sites and decreased methylation in high methylation sites
• maternal licking stimulated epigenetic processes
• MGMT methylation leads to better GBM outcomes, but also resistance to temozolamide
• heritability refers to populations NOT individuals
• heritability are your genes and enviornment
• in equal societies, heritability is high since the environment is negligible between environments
• components of variation:

  • genetic 40%
  • non-shared environment 35%
  • shared environment 5%
  • error 20%
• passive influences: parents and family may select and shape environments in ways that are similar to their own genetic environments
• with passive influences, parents reinforce pre-existing traits
• evocative influences: people illicit responses from their environments that reinforce pre-existing traits
• active influences: people search and select environments that fit their genotype (self-interests and preferences)
• personality traits are massively polygenic
• A polygenic trait is a characteristic, such as height or skin color, that is influenced by two or more genes
• genes predict educational attainment
• 3 stages of prenatal development:

  • zygote (0-2 weeks)
  • embryo (2-8 weeks)
  • fetus (8 weeks - birth)
• in the 3 stages of prenatal development, the differentiation increases
• most of the time, conception happens in the fallopian tubes
• 3 layers of cells that happen one week after conception: ectoderm, mesoderm, endoderm
• ectoderm: outer layer, nervous system, skin, hair
• mesoderm: connective tissues, muscles, blood vessels, bones
• endoderm: internal organs
• during week 3: ectodermal cells differentiate and neural plane is visible, non-neural ectoderm forms the skin
• during weeks 4-5: neural tube closure is complete, three bulges are apparent: prosencephalon, mesencephalon, rhombencephalon
• prosencephalon: telencephalon and diencephalon
• rhombencephalon: myelencephalon and metencephalon
• overview of prenatal development:

  1. neurogenesis
  2. cell migration
  3. differentiation
  4. growth of axons and dendrites
  5. apoptosis
  6. rearrangement of neural connections
• neurogenesis is the formation of new neurons and glia
• cell migration is the movement of cells into their mature location
• the growth of axons and dendrites form neural connections
• apoptosis is programmed cell death
• the rearrangement of neural connections is synaptic pruning and myelination
• neural connections are not fully myelinated until 25
• neurogenesis occurs in the ventricular zone, up to 7 weeks they are perpendicular but then turn parallel as they will migrate and stop dividing
• migration: radial glia grow out of the ventricular zone and serve as a pathway

  • 2/3 of cells use radial glia pathway, migration is not uniform, allows them to aggregate in specific structures