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Infants, Children, and Adolescents
Eighth Edition
Chapter 2
Genetic and
Environmental
Foundations
Copyright © 2016, 2012, 2008 by Laura E. Berk. All Rights Reserved
Learning Objectives (Genetics and Environment)
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1. What are genes, and how are they transmitted
from one generation to the next?
2. Describe various patterns of genetic
inheritance.
3. Describe major chromosomal abnormalities,
and explain how they occur.
5. Explain the various ways heredity and
environment may combine to influence complex
traits.
Copyright © 2016 Laura E. Berk. All Rights Reserved
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
Copyright © 2016 Laura E. Berk. All Rights Reserved
Genetic Foundations
Figure 2.2
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Meiosis
Process of cell division used to create gametes
(sex cells)
• Halves the number of chromosomes normally
present
• When sperm and ovum unite, zygote will have
46 chromosomes again.
• Ensures transmission of a constant quantity of
genetic material
Copyright © 2016 Laura E. Berk. All Rights Reserved
Twins
• Fraternal/Dizygotic: two zygotes, or
fertilized ova
• Identical/Monozygotic: one zygote that
divides into two individuals
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Maternal Factors Related to Fraternal
Twinning
• Ethnicity
• Family history of twinning
• Age
• Nutrition
• Number of births
• Fertility drugs and in vitro fertilization
Copyright © 2016 Laura E. Berk. All Rights Reserved
Patterns of Gene–Gene Interactions
Alleles inherited from the parents are either
dominant or recessive, determining:
• Physical traits
• Disabilities and diseases
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Dominant–Recessive Inheritance
Figure 2.3
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X-Linked Inheritance
• A harmful allele is carried on the X
chromosome.
• Males are more likely to be affected.
• Nature compensates: Worldwide, about 106
boys are born for every 100 girls.
Copyright © 2016 Laura E. Berk. All Rights Reserved
X-Linked Inheritance
Figure 2.4
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Genomic Imprinting and Mutation
Imprinting
• Chemical marker that activates either father’s or
mother’s gene
• Often temporary
Mutation
• Sudden, permanent change in a DNA segment
• Can occur spontaneously or be caused by
hazardous environmental agents
Copyright © 2016 Laura E. Berk. All Rights Reserved
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.
Copyright © 2016 Laura E. Berk. All Rights Reserved
Chromosomal Abnormalities
Down syndrome
• Results from problems with the 21st pair of
chromosomes
Sex chromosome abnormalities
• Results from problems with the X or Y
chromosomes
Copyright © 2016 Laura E. Berk. All Rights Reserved
Down Syndrome
• 95% of cases result from failure of 21st
chromosome pair to separate during meiosis.
• Consequences include:
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Intellectual disability
Speech problems and limited vocabulary
Slow motor development
Distinct physical features
Increased risk of Alzheimer’s disease starting around
age 40
Copyright © 2016 Laura E. Berk. All Rights Reserved
Risk of Down Syndrome and All Chromosomal
Abnormalities by Maternal Age
Figure 2.5
(From R. L. Schonberg & C. J. Tifft, 2012, “Birth Defects and Prenatal Diagnosis,” from Children with Disabilities, 7/e, M. L. Matshaw, N. J. Roizen,
& G. R. Lotrecchiano, editors, p. 50. Baltimore: Paul H. Brookes Publishing Co, Inc. Adapted by permission.)
Copyright © 2016 Laura E. Berk. All Rights Reserved
Sex Chromosomal Disorders
Disorder
Description
XYY syndrome
Above-average height; large
teeth. Normal intelligence
and sexual development.
Triple X
Tall. Impaired verbal
syndrome (XXX) intelligence. Normal sexual
development.
Klinefelter
Tall; feminine body-fat
syndrome (XXY) distribution. Impaired verbal
intelligence. Incomplete
sexual development.
Turner syndrome Short stature; webbed neck.
(XO)
Impaired spatial intelligence.
Incomplete sexual
development.
Copyright © 2016 Laura E. Berk. All Rights Reserved
Treatment
No special treatment
necessary.
Special education for verbal
ability problems.
Hormone therapy to stimulate
sexual development; special
education for verbal ability
problems.
Hormone therapy to stimulate
physical growth and sexual
development; special
education for spatial ability
problems.
Reproductive Choices
Genetic counseling helps couples assess risk of
hereditary disorders and choose family goals
accordingly.
Options:
• Conception—knowing risks
• Reproductive technologies
• Adoption
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Prenatal Diagnostic Methods
• Amniocentesis
• Chorionic villus sampling
• Fetoscopy
• Ultrasound
• Maternal blood analysis
• Preimplantation genetic diagnosis
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Fetal Medicine
• Can result in complications, the most
common being premature labor or
miscarriage
• Surgery
• Blood transfusions
• Bone marrow transplants
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Genetic Engineering
Human Genome Project
• Researchers have mapped the sequence of all human
DNA base pairs.
• Working on identifying all genes and their functions
• Thousands of genes are already identified, including those
involved in disorders of the heart, digestive system, blood,
eye, and nervous system, and many forms of cancer.
New treatments under development include gene
therapy and proteomics.
Copyright © 2016 Laura E. Berk. All Rights Reserved
Adoption
Adopted children show more learning and emotional
difficulties:
• Early stress and conflict-ridden relationships
• Children and adoptive parents less alike in
intelligence and personality
• Age at adoption can influence difficulties.
With sensitive caregiving, most children ultimately
fare well.
Copyright © 2016 Laura E. Berk. All Rights Reserved
Reproductive Technologies
• Donor insemination and in vitro fertilization
– Ethical concerns: post-menopausal
childbearing, “designer babies”
• Surrogate motherhood
– Ethical concerns: Exploitation of financially
needy women, insecurity of surrogate’s own
children
Copyright © 2016 Laura E. Berk. All Rights Reserved
Worldwide Education of Girls
Most children not enrolled in school are povertystricken girls.
Educating girls improves:
• Children’s cognitive and literacy development
• Family health
• Mother–child interactions
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Worldwide Education of Girls (continued)
The UN reports that educating girls is the
most effective means of combating:
• Poverty
• Maternal and child mortality
• Disease
• Gender inequality
• Economic and social instability
Copyright © 2016 Laura E. Berk. All Rights Reserved
Affluence
Affluent parents:
• Often physically and emotionally unavailable
• Make excessive demands for achievement
Affluent children:
• Poor academic achievement
• Alcohol and drug use
• High levels of anxiety and depression
Eating meals with parents can reduce children’s adjustment
difficulties.
Copyright © 2016 Laura E. Berk. All Rights Reserved
Neighborhoods
• After-school programs and clubs are important to
low-SES children.
– Increased self-confidence
– Better school achievement
• Attendance at neighborhood programs is often
hindered by violence.
• Family–neighborhood ties help parents.
– Parental self-worth
– Parental access to information and services
– Child-rearing support
Copyright © 2016 Laura E. Berk. All Rights Reserved
Schools
• Parent–school contact is important at all
ages.
– High-SES parents are more likely to be
involved.
– Low-SES and ethnic minority parents may feel
uncomfortable or have less time.
Copyright © 2016 Laura E. Berk. All Rights Reserved
The Cultural Context
• Culture shapes every aspect of daily life.
• Cultures vary in values; U.S. culture
emphasizes independence, self-reliance,
and privacy of the family.
• Subcultures, including ethnic minority
groups, often have cooperative family
structures
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The African-American Extended Family
Benefits of the African-American extended family:
• Helps reduce the stress of poverty and single
parenthood
• Family members help with child rearing.
• Adolescent mothers are more likely to finish high
school and get a job.
• Transmits African-American culture
Copyright © 2016 Laura E. Berk. All Rights Reserved
Heritability Estimates
• Measure the extent to which individual differences
in complex traits are due to heredity
• Obtained from kinship studies
• Estimates range from 0 to 1.00
• Limitations:
– Accuracy depends on genetic and environmental
variation in the population
– Can be misapplied
– Limited usefulness
Copyright © 2016 Laura E. Berk. All Rights Reserved
Gene–Environment Interaction
Figure 2.9
(Based on Gottlieb, 2007)
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Gene–Environment Correlation
Passive correlation
Evocative correlation
Active correlation
• Niche-picking
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Environmental Influences on Gene
Expression
Gene–environment correlation is viewed as
driven by genetics.
• Many researchers take issue with the
supremacy of heredity.
• Bidirectional influences between heredity
and environment
Adults can uncouple unfavorable gene–
environment correlations.
Copyright © 2016 Laura E. Berk. All Rights Reserved
The Epigenetic Framework
Figure 2.11
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Smoking During Pregnancy Alters
Gene Expression
• Maternal smoking and ADHD
– Prenatal tobacco exposure influences a
chromosome-5 (DD) genotype.
– In animal research, tobacco smoke
stimulates the DD genotype to release
chemicals that promote impulsivity and
overactivity.
– Smoking alters expression of the DD
genotype.
Copyright © 2016 Laura E. Berk. All Rights Reserved