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Chapter 3
HEREDITARY INFLUENCES ON
DEVELOPMENT
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 3.1 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 2 new cells
• Cells divide, 23 single chromosomes
•
Figure 3.2 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: 2 ova released
and fertilized by different sperm, are as
genetically similar as any sibling pair
•
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.
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 X’s
• Ova contain X’s, sperm an X or a Y
• Males determine sex of children
•
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.
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
•
Table 3.1 Different Levels of Gene-Environment Interaction That Influence Genetic Expression
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
•
Figure 3.5 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
– Sex-Linked Inheritance
• Genes located on sex chromosomes
• Most from recessive genes found only
on X chromosomes (common in males)
•
Figure 3.6 Normal (round) and “sickled” (elongated) red blood cells from a person with sickle-cell
anemia.
•
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 colorblind 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
•
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.
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 3.9 Sources of Congenital Defects
•
Table 3.2 Four Common Sex Chromosome Abnormalities
•
Table 3.2 Four Common Sex Chromosome Abnormalities (continued)
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 3.3 Brief Description of Major Recessive Hereditary Diseases
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
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
•
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.
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 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.
•
Figure 3.13 Photo of 3-D ultrasound of fetus.
HEREDITARY DISORDERS
• Treating Hereditary Disorders
– Special diets for metabolic disorders
– 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
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?
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
•
Figure 3.15 Concordance rates for identical and fraternal twins for several behavioral dimensions.
FROM PLOMIN ET. AL, 1994.
•
Figure 3.16 Concordance rates for identical and fraternal twins for several behavioral dimensions.
FROM PLOMIN ET AL., 1994.
•
Table 3.4 Average Correlation Coefficients for Intelligence-Test Scores from Family Studies
Involving Persons at Four Levels of Kinship
HEREDITARY INFLUENCES ON BEHAVIOR
• Contribution of Genes and Environment
–Nonshared Environmental Influences
= 1-r(identical twins reared together)
–Shared Environmental Influences
= 1 – (H + NSE)
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
HEREDITARY INFLUENCES ON BEHAVIOR
• Hereditary Influences on Intellectual
Performance
– As children age
• Genes contribute more
• Nonshared environment increases
• Shared environment decreases
•
Figure 3.17 Changes in the correlation between the IQ scores of identical and fraternal twins over
childhood. DATA FROM WILSON, 1983.
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
•
Table 3.5 Personality Resemblances among Family Members at Three Levels of Kinship
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
• 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
• The Range-of-Reaction Principle
– Genotype sets a range of possible
outcomes
– Environment largely influences where
within the range an attribute will fall
•
Figure 3.18 Hypothetical reaction ranges for the intellectual performances of three children in
restricted, average, and intellectually-enriching environments. ADAPTED FROM GOTTESMAN,
1963.
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
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
•
Figure 3.19 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 intertwined
• Criticisms
– Describes rather than explains
development