Biology and Behavior
How Children Develop
(3rd ed.)
Siegler, DeLoache & Eisenberg
Chapter 3
Class 4: genetic inf luences
Biological Foundations of Development:
Genetic Influences
How similar in appearance are you and your sibs to your parents?
Some of us look like one parent, some both, some neither.
• GENOTYPE: Set of genetic traits a person inherits
• PHENOTYPE: Set of traits a person actually displays.
Results from genotype and life experiences
Class 4: genetic inf luences
Fundamental Relations
1.
Parents’ genetic contribution to the child’s genotype
2.
Contributions of the child’s genotype to his or her own
phenotype
3.
Contribution of the child’s environment to his or her own
phenotype
4.
Influence of the child’s phenotype on his or her
environment
Class 4: genetic inf luences
Parents’
Genotype
Child’s
Genotype
Child’s
Environment
Child’s
Phenotype
Biological Foundations of Development:
Genetic Influences
Genetic Foundations
Mendel: Able to predict color of pea plant offspring.
Proposed genes: factors controlling physical traits
• Watson and Crick (1953) introduced their model of the
structure of DNA
• Scientists are attempting to figure out the function of the
25,0000 genes that make up the human genome
Class 4: genetic inf luences
Genetic Code
• We all have trillions of cells.
• Each cell has a nucleus; and each nucleus has chromosomes.
• Chromosomes (46 in humans) carry genetic information
• They are paired…except for 23rd in male (XY).
• Chromosomes made up of deoxyriboneucleic acid – DNA.
Looks like a twisted ladder – a gene is segment of this ladder.
• Genes instruct production of protein
– crucial for chemical reactions that trigger development
DNA can duplicate itself – mitosis.
This allows a single celled ovum to
become a many-celled adult
Class 4: genetic inf luences
The Sex Cells
Individuals are created when two gametes (sex cells) –
sperm/ovum - combine.
• Gametes have 23 chromosomes, which divide by meiosis.
Meiosis involves gene shuffling – crossing over – where genes
exchange chromosomes.
• Meiosis leads to variability in offspring.
Why useful?
Class 4: genetic inf luences
Multiple Offspring
• No variability occurs when a duplicating zygote splits into two.
These are identical, or monozygotic, twins (4/1000).
• Influencing factors:
• When two ova are released and both are fertilized – fraternal, or
dizygotic, twins.
Influencing factors:
Ethnicity (8/1000 whites, 14/1000 blacks),
Age (rises to 35), less for women on poor diet.
Class 4: genetic inf luences
Boy or Girl?
• Every pair of chromosomes can be distinguished.
22 match (autosomes): Longest = 1, shortest = 22.
The 23rd consists of sex chromosomes
M=X Y
F=X X
• Does an X or Y bearing sperm fertilize the ovum?
A gene on the Y chromosome encodes
the protein that triggers the formation of
the testes, which subsequently produce
testosterone, which in turn molds
maleness.
Class 4: genetic inf luences
Patterns of Genetic Inheritance
Two+ genes (alleles) occur at same place of chromosome:
one from Mom and one from Dad.
Alike alleles: child displays inherited trait (child is homozygous).
Different alleles, relationships between alleles determine trait
(heterozygous).
Dominant-Recessive (D-R) Relationships
The allele that affects characteristic is
The allele that does not is
Dominant alleles lead to certain dominant characteristics.
Two recessive alleles lead to a recessive characteristic.
Class 4: genetic inf luences
Class 4: genetic inf luences
Dominant
Recessive
Dark hair
Curly hair
Farsightedness
Type A blood
Double jointedness
Disorders and defects are often product of recessive alleles.
Class 4: genetic inf luences
Polygenic Inheritance
 When traits are governed by more than one gene
 Applies to most
traits and
behaviors of
interest to
behavioral
scientists
 Genetic Transmission of Diseases and Disorders:
cancer, heart disease, asthma, psychiatric disorders,
behavior disorders
Class 4: genetic inf luences
Phenylketonuria (PKU) is a common defect (1 in 8000)
If both parents have recessive alleles = 1 in 4 children.
PKU is lack of enzymes that neutralizes phenylalanine (proteins)
– found in milk, eggs, fish.
Causes lethargy by 5 months, retardedness by 1 year.
But, can be treated:
•Development is slowed but deficit disappears by school years
(Mazzocco et al., 1994).
Class 4: genetic inf luences
Sickle cell anemia
Affects only Black Americans.
Two recessive alleles cause round blood cells to be sickle shaped.
Cells clog blood vessels: causes pain, swelling.
• Death is common before 20, few live after 40.
Also caused by oxygen deprivation, recessive allele asserts itself.
Why Black Americans?
Class 4: genetic inf luences
Mutation
Where do harmful genes come from?
Mutation: a sudden permanent change in a segment of DNA.
May affect 1 or 2 genes, or many.
Some occur by chance, some from environmental agents.
Example:
Class 4: genetic inf luences
Ionizing radiation before birth leads to
miscarriage/children with defects.
X-Linked Inheritance
Males and females just as likely to inherit recessive disorders.
BUT, when harmful allele is carried in the X chromosome, X-linked
inheritance occurs.
• Females’ dominant X suppresses recessive X.
• Males more likely affected: their sex chromosomes do not match
– Y is shorter and often cannot override the X.
Class 4: genetic inf luences
Inheritance of Hemophilia, a Sex-Linked Disorder
Carrier Mother
X
X
X
Normal
Father
Y
From Seifert/Hoffnung, Child and
Adolescent Development, 5/e, Figure
3.8, p. 70. Used by permission of
Houghton Mifflin Company.
Class 4: genetic inf luences
XX
Normal
Daughter
(25%)
XX
Carrier
Daughter
(25%)
XY
Normal
Son
(25%)
XY
Hemophilic
Son
(25%)
Examples of X-linked inheritance
Red-Green Color Blindness : Affects males
twice as often as females (Cohen, 1984)
Miscarriage: infant and childhood death greater
for males.
Learning disabilities: behavior disorders: more
common in boys.
BUT: because Y-bearing sperm are lighter and
quicker they reach ovum more quickly.
Thus 120/100 boys to girl (and more boys
conceived).
Class 4: genetic inf luences
Genetic Imprinting
Over 1,000 traits follow D-R inheritance.
But: Genetic imprinting:
• alleles chemically marked so that the mother’s or father’s pair is
activated.
For example:
1. Diabetes comes from father
2. Asthma and hay fever come from mother
Class 4: genetic inf luences
Chromosomal Abnormalities
In addition to recessive alleles, chromosomal abnormalities cause
serious developmental problems.
Often a chromosome pair does not separate properly.
More serious than problem from single gene – involves many.
Class 4: genetic inf luences
Down Syndrome (1 in 800; 1/1900 at 20; 1/130 at 39)
Mostly from 21st pair of chromosomes fail to separate.
Individual has 3 of this chromosome rather than 2.
• Children have distinct physical features:
1.
2.
Short, stocky, flattened face, almond shape eyes.
Often have heart defects, eye cataracts.
Death: 14% by 1 year, 21% by 10, others by middle adulthood.
Class 4: genetic inf luences
FREQUENCY OF DOWN SYNDROME (PER 1000)
Figure 3.8
Relationship Between Maternal Age and the Incidence of Down Syndrome
100
90
80
70
60
50
40
30
20
10
0
15
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20
25
30
35
40
MATERNAL AGE (YEARS)
45
50
Behavioral:
1. mental retardation,
2. speech problems,
3. slow motor development –
All become worse with age.
Smile less readily, no eye contact, explore less.
BUT: Early intervention helps social and emotional skills – not
cognitive.
So, it is genetic but environmental factors affect it.
Class 4: genetic inf luences
The Family Study
 The mainstay of modern behavioral genetics
research
 A trait of interest is measured among groups of
people who vary in genetic relatedness
 Correlations for traits
measured for individuals
who
 Are genetically more
similar
 Share the same
environment
Class 4: genetic inf luences
Types of Family Studies
 Twin-Study Designs:
Correlations for pairs of
monozygotic twins on a
trait of interest are
compared to those of
dizygotic twins
 Adoption Studies:
Researchers examine
whether adopted children
are more like their
biological or their adopted
relatives
Class 4: genetic inf luences
Minnesota Study of
Twins Reared Apart
 Located and studied twin siblings who have not
met since they were infants
The team of investigators were struck by the
similarities they found in traits like IQ,
reaction to stress, and traditionalism
These similarities may be influenced by
selective placement and similarities in
fostering environments as well as by genetic
factors
Class 4: genetic inf luences
Reproductive Choices
Genetic Counseling
Helps assess chance of hereditary disorders.
High risk:
1. previous miscarriages,
2. genetic problems in family.
There is an interview, family tree is established – pedigree.
Blood tests, genetic analyses allow prediction of harmful carrier.
Should parents “take a chance”? Or adopt?
Class 4: genetic inf luences
Prenatal Diagnosis and Fetal Medicine
Methods of detection are available for those who are high risk.
Ultrasound: high-frequency sound waves give picture of fetus – gross
physical defect can be seen.
Amniocentesis; most common: needle inserted to abdominal wall.
Uterus fluid is obtained. Cells examined.
• But, can cause miscarriages or injury to fetus.
Class 4: genetic inf luences