CHILD PSYCHOLOGYCHILD PSYCHOLOGY

Canadian EditionCanadian Edition

Vasta, Miller, Ellis, Younger, GosselinPrepared by:Prepared by:

Kim O'Neil, Carleton University Kim O'Neil, Carleton University

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

DevelopmentDevelopment

Cell ChromosomesCell Chromosomes

• Cells are comprised of 3 divisions:Cells are comprised of 3 divisions:– NucleusNucleus contains the chromosomes contains the chromosomes– CytoplasmCytoplasm fills the cell interiorfills the cell interior – Cell membraneCell membrane encases the cell encases the cell

• ChromosomesChromosomes are strands of the genetic material are strands of the genetic material DNADNA– Each human cell contains 23 chromosome pairs Each human cell contains 23 chromosome pairs

(yielding 46 total chromosomes per cell)(yielding 46 total chromosomes per cell)– Autosomes comprise 22 of the 23 pairsAutosomes comprise 22 of the 23 pairs– Sex chromosomes comprise the 23rd pairSex chromosomes comprise the 23rd pair

• Males are XY, females are XXMales are XY, females are XX

Cell FunctionCell Function

• Cells form two groups based on function:Cells form two groups based on function:– Body cellsBody cells: form the structures of the body: form the structures of the body

• Reproduce by Reproduce by mitosismitosis: Forming two identical cells, : Forming two identical cells, each equipped with 23 pairs of chromosomeseach equipped with 23 pairs of chromosomes

– Germ cellsGerm cells: form the reproductive cells: form the reproductive cells• Reproduce by Reproduce by meiosismeiosis: forming four cells with each : forming four cells with each

cell containing only 23 chromosomescell containing only 23 chromosomes• These cells are the These cells are the gametesgametes: ova or sperm: ova or sperm• During conception, a sperm merges with an ovum to During conception, a sperm merges with an ovum to

form a new cell containing 23 pairs of chromosomesform a new cell containing 23 pairs of chromosomes

• MitosisMitosis refers to a refers to a process by which 2 process by which 2 identical cells are identical cells are producedproduced

(Figure adapted with permission from (Figure adapted with permission from Biology: Exploring LifeBiology: 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 3.1Figure 3.1

• MeiosisMeiosis refers to a refers to a process in 4 cells are process in 4 cells are produced, with each produced, with each containing only 23 containing only 23 chromosomeschromosomes

• During meiosis, During meiosis, the x-shaped the x-shaped chromosomes line chromosomes line up and intermix, up and intermix, yielding a novel yielding a novel genetic productgenetic product

(Figure adapted with permission from (Figure adapted with permission from Biology: Exploring LifeBiology: 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 MeiosisCross-Over During Meiosis

Figure 3.2Figure 3.2

• DNADNA is the basic genetic is the basic genetic material, formed from material, formed from pairs of base pairs of base nucleotides nucleotides – The bases form pairs The bases form pairs

such as adenosine-such as adenosine-thymine or guanine-thymine or guanine-cytosinecytosine

– The DNA strand is in The DNA strand is in the form of a double the form of a double helix made up of a helix made up of a series of base pairsseries of base pairs

Figure 3.3Figure 3.3

DNADNA

Principles of HeredityPrinciples of Heredity

• Mendel argued that certain traits are transmitted Mendel argued that certain traits are transmitted from parents to childfrom parents to child– Each trait is governed by two elements with one Each trait is governed by two elements with one

from each parentfrom each parent– PhenotypePhenotype refers to the expressed trait refers to the expressed trait– GenotypeGenotype refers to the underlying genes that govern refers to the underlying genes that govern

the traitthe trait

Principles of Genetic TransmissionPrinciples of Genetic Transmission

• Principle of dominancePrinciple of dominance: Some genes are always : Some genes are always expressed (expressed (dominant genedominant gene), others are recessive ), others are recessive ((recessive generecessive gene))

• Polygenic inheritancePolygenic inheritance occurs when traits are occurs when traits are determined by a number of genesdetermined by a number of genes

• Incomplete dominanceIncomplete dominance occurs when the dominant occurs when the dominant gene does not completely suppress the recessive gene does not completely suppress the recessive genegene

• CodominanceCodominance occurs when both genes are occurs when both genes are dominant and thus both are expresseddominant and thus both are expressed

Mendelian InheritanceMendelian Inheritance

Common Genetic TraitsCommon Genetic Traits

Dominant RecessiveBrown eyesBrown eyes Blue, gray, or green eyesBlue, gray, or green eyesNormal hairNormal hair Baldness (in men)Baldness (in men)

Dark hairDark hair Blond hairBlond hairNormal colour visionNormal colour vision Colour blindnessColour blindness

FrecklesFreckles No frecklesNo frecklesDimplesDimples No dimplesNo dimples

Genetic DisordersGenetic Disorders• Mutation refers to genetic variation (can be adaptive or Mutation refers to genetic variation (can be adaptive or

maladaptive)maladaptive)• Dominant disordersDominant disorders

– Huntington’s choreaHuntington’s chorea refers to a fatal syndrome in which refers to a fatal syndrome in which the nervous system degenerates in adulthood (age 30-the nervous system degenerates in adulthood (age 30-40)40)

• Recessive disordersRecessive disorders– PhenylketonuriaPhenylketonuria (PKU) refers to an inherited disease in (PKU) refers to an inherited disease in

which the body cannot process the amino acid which the body cannot process the amino acid phenylalaninephenylalanine

• Treatment: Eat a diet low in this amino acid during critical Treatment: Eat a diet low in this amino acid during critical periods of brain developmentperiods of brain development

– Tay-Sach’s diseaseTay-Sach’s disease and and Sickle-cell anemia (SCA)Sickle-cell anemia (SCA)

Chromosomal DefectsChromosomal Defects• Structural defects in the chromosomes refers to physical Structural defects in the chromosomes refers to physical

changes in the chromosomeschanges in the chromosomes• Autosomal disorders: Autosomal disorders:

– Down syndromeDown syndrome occurs when one pair of chromosomes has occurs when one pair of chromosomes has a third member. Results in mental retardation, poor muscle a third member. Results in mental retardation, poor muscle tone, and distinctive facial features. tone, and distinctive facial features.

– Greatest risk occurs in mothers between the ages of 45-49 Greatest risk occurs in mothers between the ages of 45-49 yearsyears

• Disorders of the sex chromosomes:Disorders of the sex chromosomes:– Fragile X syndromeFragile X syndrome is caused by an abnormal gene on the X is caused by an abnormal gene on the X

chromosome. Results in a variety of physical and chromosome. Results in a variety of physical and behavioural symptoms, including mental retardationbehavioural symptoms, including mental retardation

– Turner’s syndromeTurner’s syndrome and and Klinefelter’s syndromeKlinefelter’s syndrome

• Three principal areas of behaviourThree principal areas of behaviour– Intellectual abilitiesIntellectual abilities– Psychiatric disorders including children’s behaviour Psychiatric disorders including children’s behaviour

problemsproblems– PersonalityPersonality

• Four major approaches are used to study theFour major approaches are used to study the impact of genes on behaviourimpact of genes on behaviour– Family studiesFamily studies– Adoption studiesAdoption studies– Twin studiesTwin studies– Combined Twin Study and Adoption StudyCombined Twin Study and Adoption Study

Gene-Behaviour StudiesGene-Behaviour Studies

Family and Adoption StudiesFamily and Adoption Studies

• Family studies compare different family members Family studies compare different family members and their similarity in certain characteristicsand their similarity in certain characteristics– Explores whether the phenotypic similarity on a trait Explores whether the phenotypic similarity on a trait

follows the genotypic similarity among the people follows the genotypic similarity among the people being comparedbeing compared

• Adoption studies compare similarities in Adoption studies compare similarities in characteristics between adopted children and their characteristics between adopted children and their biological and adoptive parentsbiological and adoptive parents– Explores the contribution of shared genes versus Explores the contribution of shared genes versus

shared environment to a traitshared environment to a trait

Twin StudiesTwin Studies• Two types of twins:Two types of twins:

– Identical twins: Identical twins: MonozygoticMonozygotic ( (MZMZ) – from the ) – from the same fertilized egg same fertilized egg

– Fraternal twins: Fraternal twins: DizygoticDizygotic ( (DZDZ) – from two ) – from two different eggsdifferent eggs

• Twin studies compare the similarity between the Twin studies compare the similarity between the twins in regard to a behaviourtwins in regard to a behaviour– Concordance Concordance reflects the degree of similarity of reflects the degree of similarity of

twins on a behaviortwins on a behavior– Most studies indicate that MZ twins show greater Most studies indicate that MZ twins show greater

similarity than do DZ twins and this effect is larger similarity than do DZ twins and this effect is larger as they get olderas they get older

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

Age-Related Changes in Concordance Age-Related Changes in Concordance for MZ and DZ Twinsfor MZ and DZ Twins

Figure 3.7Figure 3.7

Models of Gene-Environment InteractionModels of Gene-Environment Interaction• Gottesman’s limit-setting modelGottesman’s limit-setting model: Range of ability is : Range of ability is

determined by genes – actual value of that ability is determined by genes – actual value of that ability is determined by the environment (determined by the environment (range of reactionrange of reaction))

• Scarr’s niche-picking modelScarr’s niche-picking model: : – Passive gene-environment correlationPassive gene-environment correlation– Evocative gene-environment correlationEvocative gene-environment correlation– Active gene-environment correlationActive gene-environment correlation

• Plomin’s environmental genetics modelPlomin’s environmental genetics model: Different : Different children experience the same environment children experience the same environment differently (differently (nonshared environmentnonshared environment))

• Bronfenbrenner Bronfenbrenner and and Ceci’s biological modelCeci’s biological model: Child’s : Child’s genes and immediate environment interactgenes and immediate environment interact

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

Range of Reaction ModelRange of Reaction ModelFigure 3.9Figure 3.9

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