Transcript Sex Chromosomes

Chapter 2
Genetic and Environmental
Foundations
Physical attractiveness of premature infants affects outcome at discharge from
the NICU
Badr, LK & Abdallah, B (2001) Infant Behavior and Development, vol. 24, p. 129+
Genetic Foundations
• Chromosomes – store and
transmit genetic information.
• Genes – segments of DNA
located along the
chromosomes
• DNA – substance of which
genes and chromosomes are
made
• less than two percent of a person's DNA represents
active genes! The rest of the DNA seems to be involved
mediating how the genes are expressed.
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Chromosomes, Cells, and Sex:
Terminology
Autosomes
Sex
Chromosomes
The 22 pairs of chromosomes that are
not sex chromosomes
23rd pair of chromosomes
 Determines sex
 XX = female, XY = male

Gametes
Sex cells: sperm and ova
Zygote
Sperm and ovum united
Twins
•Fraternal/Dizygotic
– two zygotes, or fertilized ova
•Identical/Monozygotic
– one zygote that divides into
two individuals
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Alleles
• Two forms of the same gene
 appear at the same place on both
chromosomes in a pair
 one inherited from each parent
 homozygous—the two alleles are alike
 heterozygous—the alleles differ
Genetic Principles
Homozygous: in a pair, both
genes for a trait are the
same
Eg:
Heterozygous: gene pair has 2
different gene types for
a trait
Eg:
III.
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Genetic Principles
Dominant inheritance: receive genes for contradictory
traits; dominant trait is expressed (eg: )
Recessive Inheritance: homozygous trait, receives 2 of
the same recessive genes for that trait (eg:
Examples of
Dominant
and
Recessive
Characteristics
Table 2.2
Source: McKusick, 2007.
Dominant-Recessive Inheritance
need only 1 copy of gene to show disorder
Huntington’s Disease: example of dominant inheritance
gene on chromosome 4 identified in 1993
Dad: no disease (hh)
Mom: has disease (Hh)
Mom: H
Mom: h
Dad: h
Dad: h
PKU: recessive inheritance
need 2 copies of recessive gene to show disease
Dad: carrier (Np)
Mom: carrier (Np)
Mom: N
Mom: p
Dad: N
Dad: p
X-Linked Inheritance
Figure 2.5
Sex-linked disorders
carried on X chromosome
Color-blindness: sex linked
Mutation
•Somatic Mutation:
– Normal body cells mutate, an event that can
happen at any time in life.
– The DNA defect can eventually become
widespread enough to cause disease or
disability.
•Germline Mutation:
– Takes place in the cells that give rise to
gametes
– Defective DNA is passed on to the next
generation.
Chromosomal Abnormalities
• Down syndrome
 Trisomy 21
• Sex chromosome
abnormalities
 Problems with the
number of X or Y
chromosomes
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Risk of Down Syndrome and All
Chromosomal Abnormalities
by Maternal Age
Figure 2.6
Prenatal Diagnostic Methods
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Amniocentesis
Chorionic villus sampling
Fetoscopy
Ultrasound
Maternal blood analysis
Preimplantation genetic
diagnosis (PGD)
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Karotype of DNA
Figure 2.1
Copyright © 2010 Pearson Education, Inc. All Rights
Reserved.
Genetic Principles
Polygenic Inheritance: many genes interact to affect a trait
(eg: intelligence; skin color; athleticism)
Genotype: the complete set of genes (dominant and recessive)
we’ve inherited from biological parents; present at
conception
Phenotype: the outward expression of those genes; physical
characteristics (expressed genes are influenced by pre and
post-natal factors)
Twins
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•Fraternal/Dizygotic –
two zygotes, or fertilized
ova
•Identical/Monozygotic
– one zygote that
divides into two
individuals
Genetic Methods
twin and adoption studies
Twin studies: are identical
twins (MZ) more
similar to each other
than fraternal twins
(DZ)?
MZ= monozygotic
DZ= dizygotic
Did MZ pair share a
placenta?
Placental arrangement in twins
a) Fraternal and some identical twins have
separate placentas
b) Identical twins sharing a placenta (most
MZ twins share 1 placenta)
Twin-to-twin transfusion
syndrome (identical only)
Influences on Individual Differences
Heritability (h2): variation in a trait within a
group attributable to genes
• Shared Environment: common experiences
• Non-shared Environment: unique experiences
Heritability of intelligence
Heritability of IQ
Heritability of schizophrenia
The Alternative of Adoption
 Adopted children tend to have more
learning and emotional difficulties than
other children.
 The child’s age at adoption correlates to
learning and emotional difficulties
experienced.
 Most adopted children eventually fare well.
•
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Environmental Contexts
for Development
•Family
•Socioeconomic status
•Neighborhoods
•Towns and cities
•Cultural context
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Socioeconomic Status
and Family Functioning
 Timing of family life cycle
Later parenthood (late 20s/early 30s)
 Values and expectations
 Father’s involvement
 Communication and discipline styles
 Children’s cognitive development
Affluence
 Many affluent parents are not physically and
emotionally available for their children.
 These parents often make excessive demands
for achievement.
 Adolescents whose parents value
achievement over character often have
academic and emotional problems.
Poverty
•Emotional drain
•Joblessness
•High divorce rate
•Chronic stress
•Parents < 25 with
children hardest hit
•Most homeless families
consist of women with
children under 5
Neighborhoods and Schools
• Neighborhoods offer resources and social ties that
play an important part in children’s development.
– Higher-SES families are less dependent on their
immediate surroundings than are low-SES families.
– Social ties linking families together break down in areas
with unemployment, crime, and population turnover.
• Children spend an average of 14,000 hours in
school by high school graduation.
– Parent–school contact supports development at all
ages.
The Cultural Context
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 Culture shapes every aspect of
daily life.
 Different cultures have different
values; North American culture
values the independence, selfreliance, and privacy of the
family.
 Subcultures
 Extended-family households
 Stay-at-home dad movement
The African-American
Extended Family
 Today, more black than white adults have relatives
other than their own children living in the same
household.
 The extended-family system provides emotional
support and the sharing of resources, and helps
reduce the stress of poverty and single parenthood.
 These arrangements also place a high value on
cooperation and moral and religious values.
Individualist and
Collectivist Societies
• Individualist
• Collectivist
Reaction Range
Figure 2.9
V. Genotype-Environment Correlation
• 1.
Passive Gene-Environment
• Parents who are genetically related to child provide rearing
environment
•
• 2.
Evocative (eg: attractive infant study)
• Child’s genotype elicits certain environments
•
• 3.
Active (niche-picking)
• Seek out environments that are compatible/stimulating to
your predisposition
• VIDEO: Good example of gene-environment interaction
The Epigenetic Framework
• Epigenetics: environmental influences alter
gene expression; bidirectional exchange
between heredity and environment (cellular
and social)
•
eg: ADHD (prenatal exposure changes expression of DD
genotype on chromosome 12)