1. Child Psychology A Canadian Perspective Third Edition
Younger, Adler, Vasta

2. Chapter 3 Genetics: The Biological Context of Development
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

3. Learning Objectives Learning Objective 3.1:
Identify and describe the mechanisms and processes by which physical and behavioural characteristics are inherited.
Learning Objective 3.2:
Describe different types of genetic disorders and their impact on child development.
Learning Objective 3.3:
Describe the influence that genes have on the development of psychological abilities and traits.
Learning Objective 3.4:
How do genes and environment interact to influence the development of behaviour?
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

4. Mechanisms of Inheritance: Cell Division
Cells are comprised of three divisions
Nucleus contains the chromosomes
Chromosomes: strands of the genetic material DNA
Each human cell contains 23 chromosome pairs (yielding 46 total chromosomes per cell)
Autosomes comprise 22 of the 23 pairs
Sex chromosomes comprise the 23rd pair
Males are XY, females are XX
Cytoplasm fills the cell interior
Cell membrane encases the cell
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

5. Mechanisms of Inheritance: Cell Division
Cells form two groups based on function
Body cells: form the structures of the body
Reproduce by mitosis
Forming two identical cells, each equipped with 23 pairs of chromosomes
Germ cells: form the reproductive cells
Reproduce by meiosis
Forming four cells with each cell containing only 23 chromosomes
These cells are the gametes (ova or sperm)
During conception, a sperm merges with an ovum to form a new cell containing 23 pairs of chromosomes
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

6. Mitosis refers to a process by which 2 identical cells are produced
Meiosis refers to a process in 4 cells are produced, with each containing only 23 chromosomes
Figure 3.1: (Mitosis and meiosis). Mitosis results in two cells identical with the parent and with each other. Meiosis results in four cells different from the parent cell and from each other. Adapted from Biology: Exploring Life (p.152) by G. D. Brum & L. K. McKane, 1989, New York: John Wiley & Sons. Adapted by permission of the authors.
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

7. Mechanisms of Inheritance: Cell Division
Crossing over: During meiosis, the x-shaped chromosomes line up and intermix, yielding a novel genetic product
Figure 3.2 Crossing over results in the exchange of genetic material. After the cross-over, all four strands are different. Adapted from Biology: Exploring Life (p. 44) by G. D. Brum & L. K. McKane, 1989, New York: John Wiley & Sons. Adapted by permission of the authors.
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

8. Inside the Chromosome
DNA: the basic genetic material, formed from pairs of base nucleotides
The bases form pairs such as adenosine-thymine or guanine-cytosine
The DNA strand is in the form of a double helix made up of a series of base pairs
Figure 3.3: Structure and Replication of DNA
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

9. Mendel’s Studies: Principles of Heredity
Mendel argued that certain traits are transmitted from parents to child
Each trait is governed by two elements with one from each parent
Phenotype: Expressed trait
Genotype: Underlying genes that govern the trait
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

10. Mendel’s Studies: Principles of Genetic Transmission
Principle of dominance:
Some genes are always expressed (dominant gene), others are recessive (recessive gene)
Polygenic inheritance:
Occurs when traits are determined by a number of genes
Incomplete dominance:
Occurs when the dominant gene does not completely suppress the recessive gene
Codominance:
Occurs when both genes are dominant and thus both are expressed
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

11. Mendel’s Studies: Common Genetic Traits
Dominant
Recessive
Brown eyes
Blue, gray, or green eyes
Normal hair
Baldness (in men)
Dark hair
Blond hair
Normal colour vision
Colour blindness
Freckles
No freckles
Dimples
Free earlobes
Double-jointed thumbs
No dimples
Attached earlobes
Tight thumb ligaments
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

12. Genetic Disorders: Hereditary Disorders
Mutations (genetic variations) can be adaptive or maladaptive
Dominant disorders
Huntington’s chorea:
Fatal syndrome in which the nervous system degenerates in adulthood (age 30-40)
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

13. Genetic Disorders: Hereditary Disorders
Recessive disorders
Diseases with errors of metabolism
Tay-Sachs disease:
Fatal disease in which the nervous system disintegrates because the body cannot break down fats in brain cells
Phenylketonuria (PKU):
Inherited disease in which the body cannot process the amino acid phenylalanine
Treatment: Eat a diet low in this amino acid during critical periods of brain development
Diseases without errors of metabolism
Sickle-cell anemia (SCA)
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

14. Sickle-Cell Anemia (SCA)
Figure 3.4: Scanning electron micrographs of red blood cells from normal individuals (left) and individuals with sickle-cell anemia (right). (Bill Longcore, Photo Researchers, Inc.)
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

15. Genetic Disorders
Differences between the two sex chromosomes have implications for the transmission of certain disorders called X-linked disorders
X-linked disorders: disorders that result from recessive genes located on the X chromosome, leaving males more vulnerable to them
Example: hemophelia—bleeding disorder caused by low or no blood protein essential for clotting; results from a recessive allele on the X chromosome
Other examples of X-linked disorders: Duchenne muscular dystrophy, red-green colour blindness, and fragile X syndrome
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

16. Structural Defects in the Chromosome
Autosomal disorders:
Down syndrome
21st pair of chromosomes has a third member
Results in mental retardation, poor muscle tone, and distinctive facial features
Greatest risk occurs in mothers between the ages of years
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

17. Structural Defects in the Chromosome
Disorders of the sex chromosomes:
Fragile X syndrome:
Caused by an abnormal gene on the X chromosome
Results in a variety of physical and behavioural symptoms, including mental retardation
Turner’s syndrome:
Occurs when a female has only one X chromosome (XO)
Klinefelter’s syndrome:
Occurs when a male inherits an extra X chromosome (XXY)
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

18. Studying the Effects of Genes on Behaviour
Three principal areas of behaviour
Intellectual abilities
Psychiatric disorders (including children’s behavioural problems)
Personality
Four major approaches are used to study the impact of genes on behaviour
Family studies
Adoption studies
Twin studies
Combined Twin Study and Adoption Study
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

19. Family and Adoption Studies
Family studies:
Compare different family members and their similarity in certain characteristics
Explore whether the phenotypic similarity on a trait follows the genotypic similarity among the people being compared
Adoption studies:
Compare similarities in characteristics between adopted children and their biological and adoptive parents
Explores the contribution of shared genes versus shared environment to a trait
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

20. Twin Studies Two types of twins: Identical twins – Monozygotic (MZ)
From the same fertilized egg
Fraternal twins – Dizygotic (DZ)
From two different eggs
Twin studies:
Compare the similarity between the twins in regard to a behaviour
Concordance: the degree of similarity of twins on a behavior
Most studies indicate that MZ twins show greater similarity than do DZ twins and this effect is larger as they get older
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

21. Age-Related Changes in Concordance for MZ and DZ Twins
Twin Studies
Age-Related Changes in Concordance for MZ and DZ Twins
Figure 3.7: Concordance in IQ changes in (a) identical, or monozygotic (MZ), twins and (b) fraternal, or dizygotic (DZ), twins from 3 months to 6 years of age.The scales are different to accommodate different ranges of scores.The important point is that changes in performance are more similar for monozygotic twins. Adapted from “The Louisville Twin Study: Developmental Synchronies in Behavior” by R. S.Wilson, 1983, Child Development, 54, p Copyright © 1983 by The Society for Research in Child Development, Inc. Adapted by permission.
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

22. Models of Gene-Environment Interaction
Gottesman’s limit-setting model:
Range of ability is determined by genes—actual value of that ability is determined by the environment (range of reaction)
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

23. Range of Reaction Model
Figure 3.8: The reaction range concept, showing the simultaneous influences of genes and environment. Adapted from “Developmental Genetics and Ontogenetic Psychology: Overdue Détente and Propositions from a Matchmaker” by I. I. Gottesman, In A. D. Pick (Ed.), Minnesota Symposia on Child Psychology, vol. 8, p. 60, University of Minnesota Press. Copyright © 1974 by the University of Minnesota. Adapted by permission.
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

24. Models of Gene-Environment Interaction
Scarr’s niche-picking model:
Passive gene-environment correlation
Evocative gene-environment correlation
Active gene-environment correlation
Plomin’s environmental genetics model:
Different children experience the same environment differently (nonshared environment)
Bronfenbrenner and Ceci’s biological model:
Child’s genes and immediate environment interact
Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3

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Younger, Adler, Vasta/Child Psychology, Third Edition, Chapter 3