1. CHILD PSYCHOLOGY Canadian Edition Prepared by: Kim O'Neil, Carleton University Vasta, Miller, Ellis, Younger, Gosselin Prepared by: Kim O'Neil, Carleton University

2. Chapter 3 Genetics: The Biological Context of Development

3. Cell Chromosomes Cells are comprised of 3 divisions:Cells are comprised of 3 divisions: –Nucleus contains the chromosomes –Cytoplasm fills the cell interior –Cell membrane encases the cell Chromosomes are strands of the genetic material DNAChromosomes are 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 XXMales are XY, females are XX

4. Cell Function Cells form two groups based on function: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 chromosomesReproduce 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 chromosomesReproduce by meiosis: forming four cells with each cell containing only 23 chromosomes These cells are the gametes: ova or spermThese cells are the gametes: ova or sperm During conception, a sperm merges with an ovum to form a new cell containing 23 pairs of chromosomesDuring conception, a sperm merges with an ovum to form a new cell containing 23 pairs of chromosomes

5. Mitosis refers to a process by which 2 identical cells are producedMitosis refers to a process by which 2 identical cells are produced (Figure adapted with permission from Biology: Exploring Life, by G.D. Brum and L.K. McKane, 1989, New York: John Wiley & Sons) by G.D. Brum and L.K. McKane, 1989, New York: John Wiley & Sons) Figure 3.1 Meiosis refers to a process in 4 cells are produced, with each containing only 23 chromosomesMeiosis refers to a process in 4 cells are produced, with each containing only 23 chromosomes

6. During meiosis, the x-shaped chromosomes line up and intermix, yielding a novel genetic productDuring meiosis, the x-shaped chromosomes line up and intermix, yielding a novel genetic product (Figure adapted with permission from Biology: Exploring Life, by G.D. Brum and L.K. McKane, 1989, New York: John Wiley & Sons) by G.D. Brum and L.K. McKane, 1989, New York: John Wiley & Sons) Cross-Over During Meiosis Figure 3.2

7. DNA is the basic genetic material, formed from pairs of base nucleotidesDNA is 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 DNA

8. Principles of Heredity Mendel argued that certain traits are transmitted from parents to childMendel argued that certain traits are transmitted from parents to child –Each trait is governed by two elements with one from each parent –Phenotype refers to the expressed trait –Genotype refers to the underlying genes that govern the trait

9. Principles of Genetic Transmission Principle of dominance: Some genes are always expressed (dominant gene), others are recessive (recessive gene)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 genesPolygenic inheritance occurs when traits are determined by a number of genes Incomplete dominance occurs when the dominant gene does not completely suppress the recessive geneIncomplete dominance occurs when the dominant gene does not completely suppress the recessive gene Codominance occurs when both genes are dominant and thus both are expressedCodominance occurs when both genes are dominant and thus both are expressed

10. Mendelian Inheritance

11. Common Genetic Traits DominantRecessive 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 No dimples

12. Genetic Disorders Mutation refers to genetic variation (can be adaptive or maladaptive)Mutation refers to genetic variation (can be adaptive or maladaptive) Dominant disordersDominant disorders –Huntington’s chorea refers to a fatal syndrome in which the nervous system degenerates in adulthood (age 30- 40) Recessive disordersRecessive disorders –Phenylketonuria (PKU) refers to 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 developmentTreatment: Eat a diet low in this amino acid during critical periods of brain development –Tay-Sach’s disease and Sickle-cell anemia (SCA)

13. Chromosomal Defects Structural defects in the chromosomes refers to physical changes in the chromosomesStructural defects in the chromosomes refers to physical changes in the chromosomes Autosomal disorders:Autosomal disorders: –Down syndrome occurs when one 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 Disorders of the sex chromosomes:Disorders of the sex chromosomes: –Fragile X syndrome is caused by an abnormal gene on the X chromosome. Results in a variety of physical and behavioural symptoms, including mental retardation –Turner’s syndrome and Klinefelter’s syndrome

14. Three principal areas of behaviourThree principal areas of behaviour –Intellectual abilities –Psychiatric disorders including children’s behaviour problems –Personality Four major approaches are used to study theFour major approaches are used to study the impact of genes on behaviour –Family studies –Adoption studies –Twin studies –Combined Twin Study and Adoption Study Gene-Behaviour Studies

15. Family and Adoption Studies Family studies compare different family members and their similarity in certain characteristicsFamily 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 parentsAdoption 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

16. Twin Studies Two types of twins: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 behaviourTwin studies compare the similarity between the twins in regard to a behaviour –Concordance reflects 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

17. (Figure adapted by permission from “The Louisville Twin Study: Developmental Synchronies in Behavior” by R.S. Wilson, 1983, Child Development, 34, p. 301. Copyright © 1983 by the Society for Research in Child Development). Age-Related Changes in Concordance for MZ and DZ Twins Figure 3.7

18. 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)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) Scarr’s niche-picking model: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)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 interactBronfenbrenner and Ceci’s biological model: Child’s genes and immediate environment interact

19. (Figure adapted by permission from “The Louisville Twin Study: Developmental Synchronies in Behavior” by R.S. Wilson, 1983, Child Development, 34, p. 301. Copyright © 1983 by the Society for Research in Child Development). Range of Reaction Model Figure 3.9

20. Copyright Copyright © 2006 John Wiley & Sons Canada, Ltd. All rights reserved. Reproduction or translation of this work beyond that permitted by Access Copyright (The Canadian Copyright Licensing Agency) is unlawful. Requests for further information should be addressed to the Permissions Department, John Wiley & Sons Canada, Ltd. The purchaser may make back-up copies for his or her own use only and not for distribution or resale. The author and the publisher assume no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information contained herein.