biological beginnings

Chapter 2: Biological Beginnings

Genetic FoundationsHeredity & Environment

Evolutionary Psychology

Evolution is a theory.

Survival of the fittest does not necessarily imply evolution, only a healthy population.

Natural selection based on adaptability is a circular argument.

Evolutionary Psychology

Evolutionary psychology is not new.

Popular in the early 1900’s

5000+ instincts were named

Proved to be a dead-end path

Evolutionary Psychology:Theory based on a theory

David Buss (1995, 2004) Males and females of the human species evolved

differently (e.g., spatial skills, sex) Must assume that skills are inborn or that learning

and experience changes genes in human gametes (egg/sperm)

Family curse Feminists

Evolutionary Developmental Psychology

Theory based on a theory based on a theory.

Extended juvenile period evolved so that we could learn to cope with society.

Or did society “evolve” to cope with the juvenile period?

Evolutionary Psychology Evolutionary Developmental Psychology

Human characteristics are not random. They are age and gender related.

Order and purpose are not related to random evolution, but imply the action of intelligence.

Part of the confusion has to do with teleology.

Evolutionary Developmental Psychology

Perspective here has profound effects on:

Concern for the tradition of learning/socialization

Judith Harris (Nature Assumption, 1998) says parents not important; genes and peers rule.

Views of the meaning of life

was man made for nature/society or nature for man

Genetic Foundations

DNA (deoxyribonucleic acid) a complex molecule containing the genetic

information that makes up the chromosomes

has two strands-forming a “double helix”- held together by bonds between pairs of nucleotides (spiral staircase)

Chromosomes threadlike structures made of DNA molecules that contain the genes

Genetic Foundations

Chromosomes

Human beings have 46 chromosomes (23 pairs)

Entire DNA code/set of chromosomes is repeated in each of the cells

Define the limits of species variation; separate species

Genetic Foundations

Chromosomes: limits

“Each of us carries a “genetic code” that we inherited from our parents. Because a fertilized egg carries this human code, a fertilized human egg cannot grow into an egret, eagle, or elephant.”

Genes: Our Biological Blueprint

Genes the biochemical units of heredity that make up

the chromosomes a segment of DNA capable of synthesizing a

protein

Genome the complete instructions for making an organism

Proteins are the cell building blocks and bodily process regulators

Genetics and Behavior

Nucleus Chromosome Gene

Cell DNA

Genes: Our Biological Blueprint

Human Genome Project Completed about 2000 Humans have 20,000 – 25, 000 genes (21,667) There are far more proteins than genes – 10-20 million Genes (DNA) are dependent- collaborate with other

sources of information Gene expression/activity is affected by context or

environment Context is affected by hormones, light, nutrition, etc.

Genetic Foundations

99.1% of DNA within the human race is identical

98-99% of human and chimpanzee DNA is identical

Cell Division – Gamete Production

Mitosis (normal cell division) – the nucleus of the cell & the chromosomes duplicate and divide into 2 cells. Each has the same 23 pairs of chromosomes.

Gametes (sperm and ova) have only 23 chromosomes

They are formed by meiosis rather than mitosis.

At conception, these two unite resulting in a full complement of 46 chromosomes.

A fertilized egg is called a zygote.

The Sex Cells

• Alleles are normal variations of a gene, found at the same location.

• A child who inherits the same allele (type of gene) from both parents is homozygous for that trait.

• A child who inherits different alleles from each parent is heterozygous for that trait.

Sources of Variation

Crossing over – chromosomes pair up and exchange segments during meiosis.

The probability of genetically identical, non-twin siblings is 1 in 700 trillion.

Sources of Variation

Genetic ExpressionInfluenced by the environment

hormoneslightnutritionbehaviorstress (cortisol may cause a fivefold increase in DNA damage)

Sources of Variation

Genetic Foundations

Genotype – genetic composition

Phenotype – observable characteristics

• Patterns of Genetic Inheritance•

Dominant-recessive: the dominant gene (allele) will determine the characteristic

Sources of Variation

• Patterns of Genetic Inheritance•

Dominant-recessive: the dominant gene (allele) will determine the characteristic

Sources of Variation

• Examples of dominant genes Dark hair, curly hair, dimples,

types A & B blood (vs. type O), traits for normality in vision, hearing, pigmentation, etc.

Huntington’s Disease

Patterns of Genetic InheritanceDominant-recessive inheritance

• Examples of recessive genes: Cystic fibrosis, PKU, Tay-sachs

disease. Sickle-cell anemia

Patterns of Genetic InheritanceDominant-recessive inheritance

• Co-dominance: both alleles contribute to the phenotype

• Additive: they contribute equally

• Example of Co-dominance; Sickle-cell anemia

Patterns of Genetic InheritanceCo-dominance and Additive

X-linked or Sex-linked Inheritance

Humans have 23 pairs (46 total) of chromosomes – 22 pairs are autosomes; the 23rd pair is XX in females and XY in males

• Females - X chromosome from father to match the mother’s X

• Males - Y from the father, does not have all the same genes

• Defective gene on mother’s X is offset in females, but not in males

• Examples: hemophilia, RG colorblindness

Patterns of Genetic InheritanceX-linked (sex-linked) inheritance

• Genes are chemically marked so that one member of the pair is activated regardless of its makeup.

• Important whether the trait is inherited from the mother or father.

• Examples: asthma, allergies, Huntington’s , diabetes

Sex-linked Genetic InheritanceGenetic Imprinting

Patterns of Inheritance - Polygenic

Many genes interact to influence the characteristic

Most psychological characteristics are polygenic

(Where environmental factors are included, traits are said to be multi-factorial.)

Usually happen during meiosis

Involve breakage and failure to separate

Most common are Down syndrome (trisomy 21) (1 in 700-800 live births) and sex-linked

May be mosaic (not all body cells defective)

Often result in miscarriage

Chromosomal Abnormalities

Chromosomal Abnormalities

Down Syndrome Trisomy 21: extra copy of a chromosome on the

21st pair Round face, flattened skull, potruding tongue,extra fold of skin

on eyelids, short limbs Mental and motor retardation

More common to older mothers, rare among African Americans

• Gene damaged on X chromosome

• Most common inherited cause of mild to moderate mental retardation

• Linked to autism• More common in males

Chromosomal AbnormalitiesSex-linked - Fragile X

XXY (Klinefelter) may have verbal difficulties. Tall, underdeveloped testes, possible breasts. 1/800 live male births.

XO (Turner) have trouble with math and spatial skills. Short and have webbed neck; may be infertile. 1/2500 live female births

XYY (Are they more aggressive, antisocial?)

Sex Chromosome Abnormalities

Gene-linked Abnormalities

Over 7000 known (most rare), including: Cystic fibrosis Diabetes Hemophilia Huntington PKU (phenylketonuria) Sickle-cell anemia Spina bifida Tay-sachs disease

Genetic Counseling – for whom?

Family history of disease, mental retardation, physical defects

History of miscarriages

Mother over age 35 (rate of abnormality begins to rise sharply)

May cause miscarriage (except ultrasound, maternal blood samples)

Is the problem correctible?

Genetic engineering is still in the future.

Often the only decision is whether or not to abort the fetus.

Prenatal Diagnostic Methods

Chorionic villi sampling (6-8 weeks);detects genetic defects; risk of miscarriage, limb deformity

Amniocentesis – (11 weeks, best after 15 weeks); detects genetic defects; smaller risk of miscarriage

Prenatal Diagnostic Methods

Fetoscopy – tube with light inserted into uterus; 15-18 weeks; limb & facial defects; some diseases & neural defects; some risk of miscarriage

Preimplantation genetic diagnosis –

Associated with in-vitro fertilization

Prenatal Diagnostic Methods

Infertility

1 in 6 couples in U.S. Waiting too late Sexually transmitted diseases

Fertility technology (IVF, donors) Adoption

Babies culturally unavailable

Environmental Influence

Environmental Influence

Rats reared in an environment enriched with playthings show increased development of the cerebral cortex

Impoverished environment

Enriched environment

Environmental Influence

Culture the enduring behaviors, ideas, attitudes,

and traditions shared by a large group of people and transmitted from one generation to the next

Norm an understood rule to accepted and

expected behavior norms prescribe “proper” behavior

Twins Identical Twins

develop from a single fertilized egg that splits in two, creating two genetically identical organisms

Fraternal Twins develop from separate eggs genetically no closer than

brothers and sisters, but they share a fetal environment

Identicaltwins

Fraternaltwins

Samesex only

Same oropposite sex

Dizigotic (two zygotes) Share approximately 50% of their

genetic heritage like any two siblings.

Major causes are maternal age and fertility drugs.

Twinning dramatically on the increase since the 1970s.

Multiple Births – fraternal twins

Multiple Births – identical twins

Monozygotic – one zygote (same fertilized egg)

Share 100% of genetic heritage

Occurs about 3 per 1000 live births worldwide

Factors may include temperature and oxygen levels and late fertilization

Genetics Research

Behavior Genetics

study of the power and limits of genetic and environmental influences on behavior

Molecular Genetics subfield of biology that studies the

molecular structure and function of genes

Nature-nurture Research

• Molecular genetics Human Genome Project

• Behavioral genetics Twin studies

Equal environment assumptions Adoption studies Concordance rates

Epigenesis – ongoing nature/nurture exchanges (bi-directional)

Reaction range

Canalization

Genetic-environmental correlation• Passive• Evocative• Active (niche-picking)