Vasta, Younger, Adler, Miller, Ellis Prepared by: Mowei Liu CHILD PSYCHOLOGY Second Canadian Edition Vasta, Younger, Adler, Miller, Ellis Prepared by: Mowei Liu

Genetics: The Biological Context of Development Chapter 3 Genetics: The Biological Context of Development

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?

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

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

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.

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.

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

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: the expressed trait Genotype: the underlying genes that govern the trait

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

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

Genetic Disorders: Hereditary Disorders Mutations (genetic variations) can be adaptive or maladaptive Dominant disorders Huntington’s chorea: a fatal syndrome in which the nervous system degenerates in adulthood (age 30-40)

Genetic Disorders: Hereditary Disorders Recessive disorder Diseases with errors of metabolism Tay-Sachs disease: a fetal disease in which the nervous system disintegrates because the body cannot break down fats in brain cells Phenylketonuria (PKU): an 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)

Sickle-Cell Anemia (SCA) Figure 3.5 Scanning electron micrographs of red blood cells from normal individuals (left) and individuals with sickle-cell anemia (right). (Bill Longcore/Photo Researchers, Inc.)

Structural Defects in the Chromosome Autosomal disorders: Down syndrome The 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 45-49 years

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)

Studying the Effects of Genes on Behaviour Three principal areas of behaviour Intellectual abilities Psychiatric disorders including children’s behaviour 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

Family and Adoption Studies Family studies compare different family members and their similarity in certain characteristics Explores 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

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

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. 301. Copyright © 1983 by The Society for Research in Child Development, Inc. Adapted by permission.

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)

Range of Reaction Model Figure 3.9 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, 1974. 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.

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

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