Chapter 3 Hereditary Influences on Development

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Chapter 3Hereditary Influences on Development
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The Germ (or Sex) Cells

• Hereditary uniqueness
• Male or female?
• "X" chromosome
• The longer of the two sex chromosomes
• Normal females have two X chromosomes
• Normal males have one X chromosome
• "Y" chromosome
• The shorter of the two sex chromosomes
• Normal males have one Y chromosome
• Normal females have no Y chromosome

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Principles of Heredity

• Mendel argued that certain traits are transmitted
  from parents to child
• Each trait is governed by two elements with one
  from each parent
• Phenotype refers to the expressed trait
• Genotype refers to the underlying genes that
  govern the trait

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Principles of Genetic Transmission

• Dominance Some genes are always expressed,
  others are recessive
• Segregation Each inheritable trait is passed on
  as separate unit
• Independent assortment Traits passed on
  independently of one another

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Revisions of Mendels Principles

• Polygenic inheritance Single traits may be
  products of more than one pair of genes
  (intelligence skin color)
• Incomplete dominance some genes are neither
  entirely dominant nor entirely recessive
  (sickle-cell anemia)
• Codominance For some traits, both members of a
  pair of genes are dominant.(AB blood type)

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Common Genetic Traits
RECESSIVE
DOMINANT

• Brown eyes Blue, gray, or green eyes
• Normal hair Baldness (in men)
• Dark hair Blond hair
• Color vision Color Blindness
• Freckles No freckles
• Dimples No dimples

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Genetic Disorders

• Dominant disorders
• Rarely life threatening or severely disabling
  unless expressed later in life
• Huntingtons chorea refers to a fatal syndrome in
  which the nervous system degenerates in adulthood
  (age 30-40)

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Genetic Disorders

• Recessive disorders
• Phenylketonuria (PKU)
• Tay-Sachs
• Sickle-cell anemia (caution people with only one
  gene may show characteristics (recessive
  transmission but incomplete dominance)
• Cystic fibrosis

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Structural Defects

• Down syndrome (Tri-somy 21)
• maternal age positively correlated with increased
  incidence of genotype
• due to prenatal testing, maternal age negatively
  correlated with birth of Down syndrome children

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Multiple Births

• Monozygotic (identical) twins
• A single zygote
• Later divides to form two genetically identical
  individuals
• Dizygotic (fraternal) twins
• Mother releases two ova.
• Each ova is fertilized by a different sperm.
• Two zygotes that are genetically different

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Genes

• What do genes do?
• Basic level-call for production of amino acids,
  which form enzymes and other proteins necessary
  for formation and functioning of new cells
• How are genes expressed?
• Simple dominant-recessive inheritance One allele
  dominates another so that only its phenotype is
  expressed.
• Codominance Phenotype is compromise between two
  genes.
• Sex-linked inheritance An attribute is
  determined by a recessive gene that appears on
  the X-chromosome more likely to characterize
  males.

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Genes (cont.)

• Genetic imprinting A process in which particular
  gene pairs are biochemically marked, so that only
  one parent's allele is expressed, regardless of
  its composition
• Polygenic inheritance Multiple genes influence
  many traits.

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• Figure 3.5
• Possible genotypes and phenotypes resulting from
  a mating of two heterozygotes for normal vision.

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• Figure 3.7
• Sex-linked inheritance of red/green color
  blindness. In the example
• here, the mother can distinguish reds from greens
  but is a carrier because one of her
• X chromosomes contains a color-blind allele.
  Notice that her sons have a 50 percent chance of
• inheriting the color-blind allele and being
  color-blind, whereas none of her daughters would
• display the trait. A girl can be color-blind only
  if her father is color blind and her mother is at
  least
• a carrier of the color-blindness gene.

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Chromosomal and Genetic Abnormalities

• Chromosomal abnormalities
• Abnormalities of the sex chromosomes
• Autosomal abnormalities
• Causes of chromosomal abnormalities
• Genetic abnormalities
• Recessive hereditary defects
• Mutations

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Applications

• Genetic counseling
• Prenatal detection of hereditary abnormalities
• Amniocentesis
• Chorionic villus sampling
• Ultrasound
• Treating hereditary disorders

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Methods of Studying Hereditary Influences

• Selective breeding
• Family studies
• Twin design
• Adoption design

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Estimating the Contribution of Genes and
Environment

• Gene influences
• Heritability of an attribute equals the
  correlation between identical twins minus the
  correlation between fraternal twins, all
  multiplied by a factor of 2.
• H (r identical twins - r fraternal twins) ? 2
• Nonshared environmental influences
• Nonshared environmental influences on a trait
  equal 1 (the total variation for that trait)
  minus the correlation between identical twins
  reared together.
• NSE 1 - r (identical twins reared together)

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Estimating the Contribution of Genes and
Environment (cont.)

• Shared environmental influences
• Shared environmental influences on a trait equal
  1 (the total variation for that trait) minus the
  sum of the variation attributable to genes (H)
  and nonshared environmental influences (NSE).
• SE 1 - (H NSE)

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Hereditary Influences on Intellectual
Performance and Personality

• Intellectual performance
• Longitudinal study of twins
• Adoption studies
• Hereditary contributions to personality
• How much genetic influence?
• Which aspects of environment influence
  personality?
• Measuring the effects of nonshared environments
• Do siblings have different experiences because
  they have different genes?
• Hereditary contributions to behavior disorders
  and mental illness
• Twins are usually discordant with respect to
  mental illnesses and behavior disorders.

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Hereditary and Environment as Developmental
Co-Conspirators

• The canalization principle When genes limit or
  restrict development to a small number of
  outcomes
• The range-of-reaction principle An individual
  genotype establishes a range of possible
  responses to different kinds of life experiences.
• Genotype/environment correlations
• Passive genotype/environment correlations
• Evocative genotype/environment correlations
• Active genotype/environment correlations

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Gene-Environment Interaction

• Gottesmans Limit-Setting Model
• Scarrs Niche Picking Model
• Plomins Environmental Genetics Model
• Bronfenbrenner and Cecis Bioecological Model

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Gottesmans Limit-Setting Model

• Genes set the upper and lower limits for
  development
• Environmental influences determine development
  within this reaction range

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Scarrs Niche-Picking Model (Goodness of Fit)

• Genes play an active role in three different ways
  to influence the childs environment
• Passive
• Evocative
• Active

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Plomins Environmental Genetics

• Children share many genes with their parents who,
  in turn, provide the environment for their
  children.
• Children evoke from their parents the sorts of
  responses and surroundings that suit their genes.
• Nonshared environment (NSE) explains differences
  in siblings genetic similarity explains the
  similarities in siblings.

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Bronfenbrenner and Cecis Bioecological Model
(Contextual)

• Genes exert their influence on the environment
  through proximal processes stimulating
  interactions between the child and aspects of the
  microsystem which must be frequent and continuing
  in the childs life.

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• Figure 3.13
• Hypothetical reaction ranges for the intellectual
  performances of three children in restricted,
• average, and intellectually-enriching
  environments. Adapted from Gottesman,1963.

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• Figure 3.14
• Relative influence of passive, evocative, and
  active (niche-picking) genotype/environment
  correlations as a function of age.