Psych210 quiz2&exam

Freberg_3e_PPT_ch05.pdf

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Genetics and Development of the Human Brain

Chapter Five

• The interaction between genetics (“nature”) and the environment (“nurture”) can influence physical and behavioral traits

Genetics and Behavior

• Human genome – Two sets of 23 chromosomes – Identical in almost all cells

• Genotype – Composed of alleles (homozygous vs.

heterozygous)

From Genome to Trait

• Phenotype – Gene expression converts the genetic

instructions into features of a living cell • Imprinted genes

– Expression is determined by the parental origin of the gene

From Genome to Trait (cont’d.)

Three Alleles Give Rise to Four Types of Blood

The Process of Gene Expression

• Meiosis – 223 unique egg/sperm cells can be produced

per person – Crossing over

• Mutations – Errors of DNA replication

• Sex Chromosomes – Sex-linked characteristics – X chromosome inactivation and calico cats

Sources of Genetic Variability

Cell Division by Meiosis

Crossing Over Contributes to Genetic Diversity

The X and Y Chromosomes

Probabilities of Hemophilia

X Chromosome Inactivation: Calico Cats

• Single nucleotide polymorphisms (SNPs) – DNA sequence change at one nucleotide – SNPs in the APOE gene can predict risk for

Alzheimer’s disease • Copy-number variations (CNVs)

– Variable numbers of genes or gene series – Associated with autism spectrum disorder and

schizophrenia

SNPs and CNVs

SNPs and Disease

• The contribution of genetics to the variation of a trait observed in a population – 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

Heritability

• Reversible genetic change – Not a DNA sequence change – Influenced by environmental factors

• Determines gene expression patterns – Histone modifications – DNA methylation

• Presence of methyl groups associated with gene silencing

• Abnormal DNA methylation associated with disease

Epigenetics

DNA Methylation and Histone Modification

DNA Methylation and Child Maltreatment

• Zygote forms from fusion of egg and sperm

• Early differentiation – Cell germ layers – ectoderm, mesoderm, and

endoderm – Neural plate, neural groove, neural tube – Formation of prosencephalon,

mesencephalon, and rhombencephalon

Building a Brain: Prenatal Development

Division of the Neural Tube

• Neurogenesis – 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

Nervous System Development: Neurogenesis and Migration

Neurogenesis

Radial Glia Guide the Migration of New Cells

• Differentiation of neural tube along the dorsal and ventral halves and along the rostral-caudal axis – Influenced by differentiation-inducing factors

(DIFs) – Organization of cerebral cortex affected by

intrinsic and extrinsic factors

Nervous System Development: Differentiation

• Axons and dendrites arise from neurites • Developing axons and dendrites end in

growth cones • Filapodia and lamellipodia

Nervous System Development: Axon and Dendrite Growth

Growth Cones Guide Axons to Their Targets

Growth Cones Respond to a Variety of Cues

• Synaptic specificity – neurite identification of the correct target cell

• Movement of receptors to the synaptic site is guided by presynaptic and postsynaptic structures

• Interaction with target cells influences the type of neurotransmitter released by the presynaptic cell

Nervous System Development: Formation of Synapses

• Apoptosis = programmed cell death • Access to neurotrophins influence the

survival of a neuron

Nervous System Development: Cell Death

Steps in the Formation of a Synapse at the Neuromuscular Junction

• Reduces the number of functional synapses

• Influenced by neutrophins and functionality of the synapse

Nervous System Development: Synaptic Pruning

• Occurs in rostral direction starting with the spinal cord, then hindbrain, midbrain, and forebrain

• Begins at 24 weeks postconception, with a burst around the time of birth

• Prefrontal cortex not completely myelinated until early adulthood

Nervous System Development: Myelination

Synaptic Rearrangement over the Lifespan

• Plasticity – The ability to rearrange synaptic connections

• 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

Effects of Experience on Development

Input Influences the Development of the Optic Tectum

Input from Both Eyes Competes for the Control of Target Cells in the LGN

Early Experience Affects the Organization of Ocular Dominance Columns

• Experience and social behavior – 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

– Epigenetics may play a role

Effects of Experience on Development (cont’d.)

Effects of Enriched Environments

• Neural tube defects – Anencephaly – Spinal bifida

• Genetic disorders – Down syndrome – Fragile-X syndrome – Phenylketonuria (PKU)

• Environmental toxins – Fetal alcohol syndrome

Disorders of Nervous Development

Fragile X Syndrome

Fetal Alcohol Syndrome Produces Physical and Intellectual Abnormalities

• Puberty – Surge of gray matter development and

pruning – Thickening of cortex; frontal lobe – Amygdala matures first

• Explains teen risky behavior

The Brain in Adolescence and Adulthood

White Matter Disruption and Binge Drinking

• Brain is fully mature at age 25; weight of brain starts to decrease at age 45

• Neurogenesis – Adult learning and memory – Decline of neurogenesis associated with

cognitive decline – Multiple reserves help resist loss of function

• Important to distinguish between healthy aging and disease conditions

The Adult Brain

Adult Neurogenesis