Chapter 3

Genes, Environment, and Development

• Species HereditySpecies Heredity•Genetic endowmentGenetic endowment

• Common to the speciesCommon to the species• Governs maturation and agingGoverns maturation and aging

•Human examplesHuman examples• Two eyes, sexual maturity at 12-14 yrs.Two eyes, sexual maturity at 12-14 yrs.

•Natural Selection: Genes allowing Natural Selection: Genes allowing adaptation are passed onadaptation are passed on

EvolutionEvolution• Charles Darwin (1809-1882)Charles Darwin (1809-1882)

• Species characteristicsSpecies characteristics• How they change over timeHow they change over time

• Main ArgumentsMain Arguments• Genetic variation exists in all speciesGenetic variation exists in all species

• Some genes aid in adaptationSome genes aid in adaptation

• Kettlewell’s Moths: Genetic Kettlewell’s Moths: Genetic variability provides for adaptationvariability provides for adaptation

Modern Evolutionary PerspectivesModern Evolutionary Perspectives• What we do today was adaptive for What we do today was adaptive for

ancestorsancestors• Example: mothers invest more in child Example: mothers invest more in child

rearingrearing

• Maternity is certain; paternity may not Maternity is certain; paternity may not bebe

• Evolution: gene/environment interactionEvolution: gene/environment interaction

• Traits are demanded by environmentTraits are demanded by environment

• Advantageous genes for a particular Advantageous genes for a particular environment survive environment survive

Individual Heredity - The Genetic Code

• Zygote: union of sperm and egg

– 23 pairs of chromosomes

– Each pair influences one characteristic

– Pair: One from father one from mother

• Meiosis: produces sperm and ova

• Mitosis: cell-division process

– Creates new cells

Genes: Our Biological Blueprint

Chromosomes threadlike structures made of DNA that

contain the genes DNA (deoxyribonucleic acid)

contains the genetic information that makes up the chromosomes

has two strands-forming a “double helix”--held together by pairs of nucleotides

Genes: Their Location and Composition

Nucleus Chromosome Gene

Cell DNA

Karyotype

Genes: Our Biological Blueprint

Genes biochemical units of heredity that make up

the chromosomes a segment of DNA synthesizes a protein

Genome consisting of all the genetic material in its

chromosomes

Genetic Uniqueness & Relatedness

Genetic Uniqueness & Relatedness

• Monozygotic (MZ) twins: 100% related

– 2 genetically identical individuals

• Dizygotic (DZ) twins: 50% on average

– 2 ova fertilized by 2 sperm

• Siblings: 50% on average

• Parent & Child: 50% related, shared

• Males: XY; Females: XX

• Monozygotic (MZ) twins: 100% related

– 2 genetically identical individuals

• Dizygotic (DZ) twins: 50% on average

– 2 ova fertilized by 2 sperm

• Siblings: 50% on average

• Parent & Child: 50% related, shared

• Males: XY; Females: XX

Translation of the Genetic Code

Translation of the Genetic Code

• Genes provide instructions for development

– Eye color and other characteristics

– Regulator genes turn on/off gene pairs• Adolescent growth spurt

• Shut down some in adulthood

• Genes provide instructions for development

– Eye color and other characteristics

– Regulator genes turn on/off gene pairs• Adolescent growth spurt

• Shut down some in adulthood

GenotypeGenotypeA genotype refers to person’s genetic heritage.

Copyright (c) 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

PhenotypePhenotype

• The phenotype is one’s genotype expressed in characteristics that can be observed and measured.

• It includes physical traits (e.g., height, weight) as well as psychological characteristics (intelligence, personality).

Copyright (c) 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

Copyright (c) 2001 by The McGraw-Hill Companies, Inc. All rights reserved.

Offspring with brown eyes

• Caused by hemoglobin S that reduces O2

• About 9% affected in U.S.

– Homozygous recessive (ss)

• Heterozygous: (Ss) “carriers”

– Can transmit gene to offspring

Sickle-Cell Anemia

• Incomplete dominance – carriers show signs of having recessive trait

– Will not have the disease, but sickling episodes

• Co-dominance – neither gene in pair is dominant or recessive

Sickle-Cell Anemia

Sex-Linked Inheritance• Single genes located on sex chromosomes

• Actually X-linked

• Males have no counterpart on Y chromosome

• Females have counter on second X

– Requires gene on both X’s for trait

• Hemophilia, Colorblindness

Figure 3.2

Polygenic Inheritance and Mutations

• Polygenic: Most human characteristics influenced by multiple genes

– Height, weight, intelligence, temperament

• Mutations: Change in structure/arrangement of genes

– Environmental hazards (teratogens) can cause mutations

– Produces new phenotype

– Sperm more likely than ova

– Harmful or beneficial (e.g., sickle-cell protects from malaria)

• Errors in chromosome division: Errors in chromosome division: MeiosisMeiosis•Too many or too few chromosomesToo many or too few chromosomes

• Most spontaneously abortedMost spontaneously aborted• Down syndrome: Trisomy 21Down syndrome: Trisomy 21

•Physical deformities (eyelid folds, short Physical deformities (eyelid folds, short stubby limbs, thick tongues)stubby limbs, thick tongues)

•Mental retardation Mental retardation

•Related to age of motherRelated to age of mother

Trisomy 21

Down Syndrome (Trisomy 21)Down Syndrome (Trisomy 21)

• Physical DeformitiesPhysical Deformitiesflattening of the back of the headslanting of the eyelidsshort stubby limbsthick tongues

Figure 3.3

TURNER SYNDROME (Single X chromosome - XO)

1/3000 females - short stature, sterile, webbed neck, stubby fingers, arms that turn out slightly at the elbow, and a low hairline in the back of the head

Klinefelter syndrome:1/200 males

XXY, tall, sterile, feminine traits

FRAGILE X SYNDROME Leg of X barely connected

Sex-linked: affects mostly maleseye & vision impairments Hyper-extensible joints (double jointed) elongated face Large testicles (evident after puberty) Flat feet Low muscle tone High arched palate Autism and autistic-like behavior Prominent ears hand biting and hand-flapping Mental Retardation Hyperactivity and short attention span

Genetic Diagnosis and Counseling

• Tay-Sachs disease

– Cause: recessive gene pair

– European Jews/French Canadians

• Huntington’s Disease

– Single dominant gene

• Learn about risk to unborn child

• Learn about nature, inheritance and effects of genetic disorders in family history

HUNTINGTON’S DISEASE

rapid, jerky involuntary movementsdifficulty in speaking and swallowingcognitive decline, depression, and occasionally delusionshallucinations and obsessive compulsive disorders.

Behavioral Genetics • Genetic/environment cause of trait

• Heritability estimates (genetic)

• Methods of studying– Experimental and selective breeding – attempt

to breed particular traits into animals• Tryon’s maze-bright rats indicate that activity level,

emotion, sex drive may have strong genetic basis

– Twin, adoption, family studies• Reared together or apart

• Concordance rates

Figure 3.4

Estimating InfluencesEstimating Influences• Genetic similarity

– Degree of trait similarity in family members

• Shared environmental influences

– Living in the same home

• Non-shared environmental influences

– Unique experiences (e.g., emotionality)

• Genetic similarity

– Degree of trait similarity in family members

• Shared environmental influences

– Living in the same home

• Non-shared environmental influences

– Unique experiences (e.g., emotionality)

Accounting for Individual Differences

Accounting for Individual Differences

• Correlations highest in identical twins

– Genetic factors determine trait

• Correlations higher if twins reared together

– Environmental factors

• Correlations are not perfect

– Non-shared experiences

• Identical twins more alike with age

• Correlations highest in identical twins

– Genetic factors determine trait

• Correlations higher if twins reared together

– Environmental factors

• Correlations are not perfect

– Non-shared experiences

• Identical twins more alike with age

Temperament and Personality

• Temperament – set of tendencies concerning emotional reactivity, activity, and sociability (genetic)

• Temperament correlations

• MZ twins = .50 to .60

• DZ twins = 0

• Personality correlations similar

• DZ shared environment unimportant

• Same home - different personalities

• Non-shared environment and genes important

Psychological Disorders• Schizophrenia concordance rates

– MZ = 48%: DZ=17%

– Affected parent increases risk: 13%

• Inherited predisposition

– Environmental factors – triggers

– Prenatal exposure to infection suspected

Gene/Environment Correlations• E.g., Sociable genes

• Passive G/E correlations – parents’ genes influence the environment they provide for children, as well as the genes the child receives

• Parents create social home

• Evocative G/E correlations – child’s genotype evokes certain reactions

• Smiley baby gets more social stimulation

• Active G/E correlations – child’s genotype influences the environment that he/she seeks

• Child seeks parties, friends, groups, etc.

Genetic Influences on Environment• Finding: Parents who read to their children have

brighter children. Why?

• Environment: reading to child makes them brighter

• Genetic: brighter parents more informed or they enjoy reading themselves

• Finding: Aggressive children have hostile parents.

• Genetic: inherited behaviors

• Environment: growing up with negative, hostile parents causes the behavior

Controversies Surrounding Genetic Research• Identification of carriers of diseases and

disorders

• Giving information which leads to abortion

• Experimenting with techniques for genetic alteration

• Better parenting if child’s genetic predispositions understood