Chapter 3 HEREDITARY INFLUENCES ON DEVELOPMENT

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Chapter 3 HEREDITARY INFLUENCES ON DEVELOPMENT
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PRINCIPLES OF HEREDITARY TRANSMISSION

• Development begins at conception
• Sperm cell penetrates ovum
• Zygote is formed
• 46 chromosomes (23 from each parent)
• Genes, stretches of DNA
• Provides biological basis for development

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PRINCIPLES OF HEREDITARY TRANSMISSION

• Growth of Zygote, Production of Body Cells
• Zygote replicates through mitosis
• Each division duplicates chromosomes
• Each new cell contains the 46 we inherited at
  conception

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• Figure 3.1 Mitosis the way that cells replicate
  themselves.

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PRINCIPLES OF HEREDITARY TRANSMISSION

• The Germ Cells (produce sperm and ova)
• Production of Gametes through Meiosis
• Duplication of 46 chromosomes
• Crossing-over adjacent chromosomes break and
  exchange segments of genes
• Pairs of duplicated chromosomes segregate into 2
  new cells
• Cells divide, 23 single chromosomes

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• Figure 3.2 Diagram of the meiosis of a male germ
  cell.

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PRINCIPLES OF HEREDITARY TRANSMISSION

• The Germ Cells
• Hereditary Uniqueness
• Independent assortment each chromosome pair
  segregates independently, resulting in genetic
  uniqueness

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PRINCIPLES OF HEREDITARY TRANSMISSION

• Multiple Births
• Monozygotic twins single zygote divides, are
  genetically identical
• Dizygotic (fraternal) twins 2 ova released and
  fertilized by different sperm, are as genetically
  similar as any sibling pair

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• Figure 3.3 Identical, or monozygotic, twins
  (left) develop from a single zygote. Because they
  have inherited identical sets of genes, they look
  alike, are the same sex, and share all other
  inherited characteristics. Fraternal, or
  dizygotic, twins (right) have no more genes in
  common than siblings born at different times.
  Consequently, they may not look alike (as we see
  in this photo) and may not even be the same sex.

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PRINCIPLES OF HEREDITARY TRANSMISSION

• Male or Female
• Karyotypes chromosomal portraits
• 22 pairs (autosomes) are similar in males and
  females
• 23rd pair are the sex chromosomes
• Males X and Y, Females 2 Xs
• Ova contain Xs, sperm an X or a Y
• Males determine sex of children

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• Figure 3.4 These karoytypes of a male (left) and
  a female (right) have been arranged so that the
  chromosomes could be displayed in pairs. Note
  that the twenty-third pair of chromosomes for the
  male consists of one elongated X chromosome and a
  Y chromosome that is noticeably smaller, whereas
  the twenty-third pair for the female consists of
  two X chromosomes.

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PRINCIPLES OF HEREDITARY TRANSMISSION

• What Do Genes Do?
• Produce enzymes and proteins necessary for
  creation and functioning of cells
• Guide cell differentiation
• Regulate the pace/timing of development
• Environmental factors (internal and external)
  influence how genes function

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• Table 3.1 Different Levels of Gene-Environment
  Interaction That Influence Genetic Expression

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PRINCIPLES OF HEREDITARY TRANSMISSION

• How are Genes Expressed?
• Single-Gene Inheritance Patterns
• Simple Dominant-Recessive Inheritance
• 1 pair of genes (alleles), 1 from each parent
• Either dominant or recessive
• Homozygous same alleles
• Heterozygous different alleles

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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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PRINCIPLES OF HEREDITARY TRANSMISSION

• How are Genes Expressed?
• Codominance
• Phenotype is a compromise between the dominant
  and recessive alleles
• Sex-Linked Inheritance
• Genes located on sex chromosomes
• Most from recessive genes found only on X
  chromosomes (common in males)

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• Figure 3.6 Normal (round) and sickled
  (elongated) red blood cells from a person with
  sickle-cell anemia.

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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-blind gene.

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PRINCIPLES OF HEREDITARY TRANSMISSION

• How are Genes Expressed?
• Polygenic Inheritance
• Characteristics influenced by many pairs of
  alleles
• Most complex human attributes are polygenic

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• Figure 3.8 Single-gene and multiple gene
  distributions for traits with additive gene
  effects. (a) A single gene with two alleles
  yields three genotypes and three phenotypes. (b)
  Two genes, each with two alleles, yield nine
  genotypes and 5 phenotypes. (c) Three genes,
  each with two alleles, yield twenty-seven
  genotypes and seven phenotypes. (d) Normal
  bell-shaped curve of continuous variation.

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HEREDITARY DISORDERS

• Congenital defects present at birth (5)
• Chromosomal Abnormalities too many or too few
• Sex Chromosome Abnormalities
• Abnormalities of the Autosome
• Down syndrome most common trisomy-21 (extra
  21st chromosome)

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• Figure 3.9 Sources of Congenital Defects

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• Table 3.2 Four Common Sex Chromosome Abnormalities

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• Table 3.2 Four Common Sex Chromosome
  Abnormalities (continued)

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HEREDITARY DISORDERS

• Genetic Abnormalities
• Many passed to children by parents who are
  carriers of recessive alleles
• Some are caused by dominant alleles
• Some result from mutations changes in structure
  of one or more genes
• Spontaneous
• Environmental hazards

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• Table 3.3 Brief Description of Major Recessive
  Hereditary Diseases

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HEREDITARY DISORDERS

• Predicting Hereditary Disorders
• Genetic counseling both chromosomal and genetic
  abnormalities
• Obtain a pedigree family history
• DNA from parents blood
• Consider options based on risk

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HEREDITARY DISORDERS

• Detecting Hereditary Disorders
• Amniocentesis withdrawal of a sample of
  amniotic fluid, tests fetal cells within fluid
• Risk of miscarriage higher than risk of birth
  defect in women younger than 35
• Conducted 11th/14th week of pregnancy
• Results 2 to 3 weeks later

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• Figure 3.11 In amniocentesis, a needle is
  inserted through the abdominal wall into the
  uterus. Fluid is withdrawn and fetal cells are
  cultured, a process that takes about 3 weeks.

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HEREDITARY DISORDERS

• Detecting Hereditary Disorders
• Chorionic villus sampling collects cells from
  chorion,
• Conducted 8th/9th week of pregnancy
• Results in 24 hours
• Risk of miscarriage 1 in 50
• Ultrasound sound waves provide outline of fetus
  useful after 14th week, safe

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• Figure 3.12 Chorionic villus sampling can be
  performed much earlier in pregnancy, and results
  are available within 24 hours. Two approaches to
  obtaining a sample of chorionic villi are shown
  here inserting a thin tube through the vagina
  into the uterus or a needle through the abdominal
  wall. In either of these methods, ultrasound is
  used for guidance. ADAPTED FROM MOORE PERSAUD,
  1993.

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• Figure 3.13 Photo of 3-D ultrasound of fetus.

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HEREDITARY DISORDERS

• Treating Hereditary Disorders
• Special diets for metabolic disorders
• Fetal surgery, hormone therapy
• Gene replacement therapy relieves symptoms,
  doesnt cure disorder
• Germline gene therapy replace harmful genes
  early in embryonic stage to cure defect not yet
  used in humans

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HEREDITARY INFLUENCES ON BEHAVIOR

• Behavioral genetics - study of how genes and
  environment influence behavior
• Methods of studying hereditary influences
• Selective breeding animal studies
• Family studies examining kinship
• Twin studies identical vs. fraternal
• Adoption studies children similar to biological
  or adoptive parents?

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HEREDITARY INFLUENCES ON BEHAVIOR

• Contribution of Genes and Environment
• Concordance rates - of pairs of people who both
  display a trait if one member has it
• Gene Influences
• Heritability coefficient (r identical r
  fraternal) X 2

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• Figure 3.15 Concordance rates for identical and
  fraternal twins for several behavioral
  dimensions. FROM PLOMIN ET. AL, 1994.

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• Figure 3.16 Concordance rates for identical and
  fraternal twins for several behavioral
  dimensions. FROM PLOMIN ET AL., 1994.

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• Table 3.4 Average Correlation Coefficients for
  Intelligence-Test Scores from Family Studies
  Involving Persons at Four Levels of Kinship

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HEREDITARY INFLUENCES ON BEHAVIOR

• Contribution of Genes and Environment
• Nonshared Environmental Influences
• 1-r(identical twins reared together)
• Shared Environmental Influences
• 1 (H NSE)

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HEREDITARY INFLUENCES ON BEHAVIOR

• Myths about Heritability Estimates
• Cannot tell us if we have inherited a trait
• Differences among individuals due to differences
  in inherited genes
• Only apply to populations under particular
  environmental circumstances
• Clearly heritable traits CAN be modified by
  environmental influences

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HEREDITARY INFLUENCES ON BEHAVIOR

• Hereditary Influences on Intellectual Performance
• As children age
• Genes contribute more
• Nonshared environment increases
• Shared environment decreases

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• Figure 3.17 Changes in the correlation between
  the IQ scores of identical and fraternal twins
  over childhood. DATA FROM WILSON, 1983.

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HEREDITARY INFLUENCES ON BEHAVIOR

• Hereditary Contributions to Personality
• Introversion/extraversion and empathetic concern
  are both genetically influenced
• Moderate heritability (.40)
• Nonshared environmental influences are also
  important
• Shared environmental influences are relevant for
  religious social values

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• Table 3.5 Personality Resemblances among Family
  Members at Three Levels of Kinship

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HEREDITARY INFLUENCES ON BEHAVIOR

• Hereditary Contributions to Behavior Disorders
  and Mental Illness
• Schizophrenia, alcoholism, criminality,
  depression, hyperactivity, bipolar disorder,
  neurotic disorders all genetically influenced
• Inherit a predisposition, not the disorder

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THEORIES OF HEREDITARY AND ENVIRONMENTAL
INTERACTIONS

• The Canalization Principle
• Multiple pathways individuals may develop
• Nature and nurture combine to determine pathway
• Either genes or environment may limit the extent
  the other can influence development

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THEORIES OF HEREDITARY AND ENVIRONMENTAL
INTERACTIONS

• The Range-of-Reaction Principle
• Genotype sets a range of possible outcomes
• Environment largely influences where within the
  range an attribute will fall

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• Figure 3.18 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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THEORIES OF HEREDITARY AND ENVIRONMENTAL
INTERACTIONS

• Genotype-Environment Correlations
• Passive home environment is influenced by
  parents genotypes
• Evocative genetically influenced attributes
  affects behavior of others toward the child
• Active environments children seek will be
  compatible with genetic predispositions

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THEORIES OF HEREDITARY AND ENVIRONMENTAL
INTERACTIONS

• How Do Genotype-Environment Correlations
  Influence Development?
• Passive important when young
• Evocative remain important throughout
  development
• Active important as a child matures

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• Figure 3.19 Relative influence of passive,
  evocative, and active (niche-picking)
  genotype/environment correlations as a function
  of age.

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CONTRIBUTIONS AND CRITICISMS OF THE BEHAVIORAL
GENETICS APPROACH

• Contributions
• Many attributes thought to be environmentally
  determined are influenced by genes
• Genetics and environment intertwined
• Criticisms
• Describes rather than explains development