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HEREDITARY INFLUENCES ON DEVELOPMENT
HEREDITARY INFLUENCES ON DEVELOPMENT
• Genotype: genes that one inherits
• Phenotype: how one’s genotype is
expressed in observable or measurable
characteristics
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
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
•
Figure 2.1 Mitosis: the way that cells replicate themselves.
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
two new cells
• Cells divide, 23 single chromosomes
•
Figure 2.2 Diagram of the meiosis of a male germ cell.
PRINCIPLES OF HEREDITARY TRANSMISSION
• The Germ Cells
– Hereditary Uniqueness
• Independent assortment – each chromosome pair
segregates independently, resulting in genetic
uniqueness
PRINCIPLES OF HEREDITARY TRANSMISSION
• Multiple Births
– Monozygotic twins: single zygote divides, are
genetically identical
– Dizygotic (fraternal) twins: two ova released
and fertilized by different sperm, are as
genetically similar as any sibling pair
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 (typically), Females – 2 X’s
(typically)
• Ova contain X’s, sperm an X or a Y
• Males determine sex of children
FOCUS ON RESEARH: CROSSING-OVER AND
CHROMOSOME SEGREGATION DURING MEIOSIS
• During Meiosis
– Chromosomes duplicate
– Chromosomes swap genetic material at a
chiasma
• 42 events during meiosis for females
• 27 events for males
• More likely at certain spots (hotspots)
– Increases genetic variability
– Chiasma reduces likelihood of aneuploidy:
FOCUS ON RESEARH: CROSSING-OVER AND
CHROMOSOME SEGREGATION DURING MEIOSIS
• Meiosis
– Benefits
• Increases genetic variability
• Chiasma reduces likelihood of aneuploidy: incorrect
number of chromosomes
•
Figure 2.3 A chromosome that had duplicated in preparation for meiosis. Used by permission of Julia Cline.
•
Figure 2.4 Recombination via crossing-over between homologous grandparent genes during meiosis and
four of the 16 possible zygote combinations. Used by permission of Julia Cline.
PRINCIPLES OF HEREDITARY TRANSMISSION
• What Do Genes Do?
– Produce amino acids which 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
•
Table 2.1 Different Levels of Gene-Environment Interaction That Influence Genetic Expression Source:
Adapted from Johnson, 2005.
PRINCIPLES OF HEREDITARY TRANSMISSION
• How are Genes Expressed?
– Single-Gene Inheritance Patterns
• Simple Dominant-Recessive Inheritance
–
–
–
–
one pair of genes (alleles), one from each parent
Either dominant or recessive
Homozygous – same alleles
Heterozygous – different alleles
» Will then be a carrier for the recessive trait
•
Figure 2.5 Possible genotypes (and phenotypes) resulting from a mating of two heterozygotes for normal
vision.
PRINCIPLES OF HEREDITARY TRANSMISSION
• How are Genes Expressed?
– Codominance
• Phenotype is a compromise between the dominant
and recessive alleles
– Examples:
» Blood Type
» Sickle-cell trait
•
Figure 2.6 Normal (round) and “sickled” (elongated) red blood cells from a person with sickle -cell anemia.
PRINCIPLES OF HEREDITARY TRANSMISSION
• How are Genes Expressed?
– Sex-Linked Inheritance
• Genes located on sex chromosomes
• Most from recessive genes found only on X
chromosomes (common in males)
• More than 100 sex-linked characteristics
•
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.
PRINCIPLES OF HEREDITARY TRANSMISSION
• How are Genes Expressed?
– Polygenic Inheritance
• Characteristics influenced by many pairs of alleles
• Most complex human attributes are polygenic
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)
•
Figure 2.8 Sources of congenital defects.
•
Table 2.2 Four
Common Sex
Chromosome
Abnormalities
Sources:
Robinson et
al., 1992;
Plomin et al.,
1997; Shafer
and Kuller,
1996.
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
•
Table 2.3 Brief Description of Major Recessive Hereditary Diseases. Sources: Kuller, Cheschier, & Cefalo,
1996; Strachan & Read, 1996.
HEREDITARY DISORDERS
• Predicting Hereditary Disorders
– Genetic counseling – both chromosomal and
genetic abnormalities
– Determine likelihood of transmitting disorder
to children
• Obtain a pedigree – family history
• DNA from parents’ blood
• Consider options based on risk
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 two to three weeks later
•
Figure 2.9 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. Adapted from Before We Are
Born, 4th ed., by K. L. Moore & T. V. N. Persaud, 1993, p. 89. Philadelphia: Saunders. Adapted with permission
of the author and publisher.
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
•
Figure 2.10 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 Before We Are Born, 4th ed., by K. L. Moore & T. V.
N. Persaud, 1993, p. 89. Philadelphia: Saunders. Adapted with permission of the author and publisher.
HEREDITARY DISORDERS
• Treating Hereditary Disorders
– Special diets for metabolic disorders (PKU)
– Fetal surgery, hormone therapy
– Gene replacement therapy – relieves
symptoms, doesn’t cure disorder
– Germline gene therapy – replace harmful
genes early in embryonic stage to cure defect;
not yet used in humans (ethical issues?)
HEREDITARY INFLUENCES ON BEHAVIOR
• Behavioral genetics: study of how genotype
interacts with environment to determine
behavioral attributes
– Methods of studying hereditary influences
• Selective breeding – animal studies
• Family studies – examining kinship
– Twin design – identical vs. fraternal
– Adoption design – children similar to biological or
adoptive parents?
•
Figure 2.11 Maze-running performance by inbred mazebright and mazedull over 18 generations. From
Behavioral Genetics: A Primer, 3rd ed., by R. Plomin, J. C. DeFries, & G. E. McClearn, 1997. Copyright © W. H.
Freeman and Company.
HEREDITARY INFLUENCES ON BEHAVIOR
– Methods of studying hereditary influences
• 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
• Nonshared Environmental Influences
= 1-r(identical twins reared together)
• Shared Environmental Influences
= 1 – (H + NSE)
•
Figure 2.12 Concordance rates for homosexuality in 110 male twin pairs. From the higher concordance for
the identical twin pairs, we can infer that genes influence one’s sexual orientation. Based on “A Genetic
Study of the Male Sexual Orientation,” by J. M. Bailey and R. C. Pillard, 1991, Archives of General Psychiatry,
48, 1089-1096. Copyright 1991 by the Archives of General Psychiatry. Adapted by permission.
•
Figure 2.13 Concordance rates for identical and fraternal twins for several behavioral dimensions. From R. Plomin, M. J.
Owen, and P. McGuffin, “The genetic basis of complex human behaviors,” Science, 264, 1733-1739. Copyright © 1994
by the American Association for the Advancement of Science. Reprinted by permission.
•
Table 2.4 Average Correlation Coefficients for Intelligence-Test Scores from Family Studies Involving Persons
at Four Levels of Kinship. Source: Based on “Family studies of Intelligence: A Review,” by T. J. Bouchard Jr., &
M. McGue, 1981. Science, 212, pp. 1055-1059.
HEREDITARY INFLUENCES ON BEHAVIOR
– Myths about Heritability Estimates
• Cannot tell us if we have inherited a trait
• Does not apply to individuals
– 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
HEREDITARY INFLUENCES ON BEHAVIOR
• Hereditary Influences on Intellectual
Performance
– As children age
• Role of genes increases
• Nonshared environment increases
• Shared environment decreases
•
Figure 2.12 Changes in the correlation between the IQ scores of identical and fraternal twins over childhood. From
“The Louisville Twin Study: Developmental Synchronies in Behavior,” by R. S. Wilson, 1983, Child Development, 54, pp.
298-316. Copyright © 1983 by The Society for Research in Child Development, Inc. Reprinted by permission.
HEREDITARY INFLUENCES ON BEHAVIOR
• Hereditary Contributions to Personality
– Introversion/extraversion and empathetic
concern are both genetically influenced
– Moderate heritability (+.40)
– Nonshared environmental influences are most
important
•
Table 2.5 Personality Resemblances among Family Members at Three Levels of Kinship. Sources: Loehlin,
1985, Loehlin & Nichols, 1976.
HEREDITARY INFLUENCES ON BEHAVIOR
• Aspects of Environment Influencing
Personality
– Nonshared environmental influences
• Differing parental treatment
• Sibling interaction
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
THEORIES OF HEREDITARY AND ENVIRONMENTAL
INTERACTIONS IN DEVELOPMENT
• Canalization – genetic restriction of
phenotype to small number of outcomes
• 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
THEORIES OF HEREDITARY AND ENVIRONMENTAL
INTERACTIONS IN DEVELOPMENT
• The Range-of-Reaction Principle
– Genotype sets a range of possible outcomes
– Environment largely influences where within
the range an attribute will fall
•
Figure 2.13 Hypothetical reaction ranges for the intellectual performances of three children in restricted, average, and
intellectually-enriching environments. Adapted from “Heritability of Personality: A Demonstration,” by I. Gottsman,
1963, Psychological Monographs, 11 (Whole No. 572). Copyright © 1963 by the American Psychological Association.
THEORIES OF HEREDITARY AND ENVIRONMENTAL
INTERACTIONS IN DEVELOPMENT
• 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
THEORIES OF HEREDITARY AND ENVIRONMENTAL
INTERACTIONS IN DEVELOPMENT
• How Do Genotype-Environment
Correlations Influence Development?
– Passive – important when young
– Evocative – remain important throughout
development
– Active – important as a child matures
•
Figure 2.14 Relative influence of passive, evocative, and active (niche-picking) genotype/environment
correlations as a function of age.
CONTRIBUTIONS AND CRITICISMS OF THE
BEHAVIORAL GENETICS APPROACH
• Contributions
– Many attributes thought to be environmentally
determined are influenced by genes
– Genetics and environment interact
• Criticisms
– Describes, does not explain development
– Environmental forces are unspecified
THE ETHOLOGICAL AND
EVOLUTIONARY VIEWPOINTS
• Ethology: scientific study of evolutionary basis
of behavior and the contributions of evolved
responses to survival and development
– Assumptions of Classical Ethology:
• Born with biologically programmed behaviors
(through natural selection)
– Products of evolution
– Adaptive to survival
THE ETHOLOGICAL AND
EVOLUTIONARY VIEWPOINTS
• Assumptions of Ethology
– Focus on instinctual responses that
• All members of species share
• May steer individuals along similar developmental
paths
– Study subjects in natural environment
THE ETHOLOGICAL AND
EVOLUTIONARY VIEWPOINTS
• Ethology and Human Development
– Crying (for example)
• Ensures infant’s basic needs are met
• Ensures sufficient contact to form primary emotional
attachments
– Critical periods: limited time span when organisms
are biologically prepared to display adaptive
patterns of development, given right input
THE ETHOLOGICAL AND
EVOLUTIONARY VIEWPOINTS
• Ethology and Human Development
– Sensitive periods:
• Optimal time for emergence of behaviors
• Particularly sensitive to environmental influences
• Development can occur outside a sensitive period, but
is more difficult
THE ETHOLOGICAL AND
EVOLUTIONARY VIEWPOINTS
• Modern Evolutionary Theory
– Adaptive motives and behaviors ensure survival
and spread of an individual’s genes
• Individual can die if family member survives, as they
carry his or her genes
THE ETHOLOGICAL AND
EVOLUTIONARY VIEWPOINTS
• Contributions
– Children have adaptive, genetically
preprogrammed characteristics that influence
development.
– Value of studying human development in normal,
everyday settings
– Value of comparing human development with that
of other species
THE ETHOLOGICAL AND
EVOLUTIONARY VIEWPOINTS
• Criticisms
– Difficult to test
– Learning tends to modify most biological
predispositions