HEREDITY AND ENVIRONMENT

Chapter 2

Molecular Genetics

Chromosomes, Gene, and Cell

Division

Genetic Disorders

Behavior Genetics

Environmental Influences and

Contexts

Environment in a Broader

Context: Family and Culture

Heredity and Environment

DNA is a complex molecule made up of nucleotides and four different bases

Bases form base pairs that should not vary

Basic units of inheritance are genes-delineated pieces of DNA

There are about 25,000 genes in human body

Molecular Genetics

Major Features of a Typical Cell

Note the twisted ladder-like structure, referred to as a double helix. Base pairs form the rungs on the DNA ladder, (here in blue and purple), and their sequence determines the genetic traits that are carried in the DNA of each individual.

Computer-Generated Stimulation of DNA Molecule

Segment of DNA Visualized as Ladder

How Can Such a Simple System Dictate How Life Unfolds?

• Number of base pairs in DNA molecule are very large

• Different species, and even different individuals within the same species, have different numbers of base pairs in their genome

• Order of pairing is important

According to the Human Genome Project, all humans are 99.9% genetically identical.

Protein synthesisMost significant thing genes do

is build proteins

Proteins are molecules that control life

Over 200,000 different proteins have been identified in humans

What Is Protein Synthesis?

Common Proteins and Their Functions in the Human Body

When cell divides, DNA assembles into chromosomes

Chromosomes are chains of genes that can be observed directly

All cells except sperm and egg cells contain 23 pairs of chromosomes

First 22 of those pairs are matching, and are referred to as autosomes

The 23rd pair determines sex selection and is labeled XX in females and XY in males

One’s chromosomal makeup can be visualized in karyotypes

Genes, Chromosomes, and Cell Division

Human Karyotypes

Mitosis Cells divide and create two cells with identical sets of chromosomes

MeiosisCell division produces ova and

sperm, each of which contain one half of the full set of chromosomes

Genotype Genes individual inherits

Genes Exist in pairs, each half of which is an allele

Cell Division and Reproduction

Comparison of Mitosis and Meiosis

• All of person’s pairs of alleles that form their genetic code

• Dominant allele• Recessive allele• Dominant trait

expression• Recessive trait

expression

Genotype

From Genotype to Phenotype

From Genotype to Phenotype

Simple dominance and recessive

•When an allele is dominant, its presence in gene pair has tendency to cause that trait to be expressed characteristic or trait•Homozygous•Heterozygous

Combination of genes

•Combinations of many gene pairs determine most traits•Polygenetic inheritance

Examples of Dominant-Recessive Gene Combinations

• Determined by more than one gene pair

Polygenic human

characteristics

• Usually passed on by X chromosome

Sex-linked traits

Hypothetically, the same parents can produce hundreds of trillions of unique children.

Genetic Inheritance

•May occur during mitosis or meiosis when DNA molecule is altered during cell division•May be beneficial or detrimental

Genetic mutations

Genetic Inheritance

Genetic anomalies

•Involve problems with instructional mechanism of genetic process

Sex-linked disorders

•Can occur when gametes do not replicate correctly or when genetic information, even entire chromosomes, are missing or duplicated

Genetic and Chromosomal Disorders

Crossing Over of Chromosomes

Sometimes during meiosis parts of chromosomes cross over, which creates new combinations of genes on a chromosome.

Source: Derived from Life (4th ed.), by R. Lewis, D. Gaffin, M. Hoefnagels, and B. Parker,2002, New York: McGraw-Hill.

Gene-Environment Interactions:The Study of Epigenetics

Individuals differ not only in their genes, but also in

specific ways in which they experience their

environments

Environmental forces can change gene expressions

Gene-environment interactions occur

at many levels

Experience in life can have dramatic effect on

later developmental outcomes

Epigenetic modifications may be transmitted to

next generation via genetic inheritance

Some sex-linked disorders

Color blindness,

X-linked

Chromosomal

Fragile X syndrome

Klinefelter syndrome

(XXY, XXXY, XXXXY)

Superfemale syndrome

(XXX, XXXX, XXXXX)

Supermale syndrome

(XYY, XYYY, XYYYY)Turner

Syndrome (OX)

Some Sex-Linked Disorders

Autosomal disorders

Genetic (recessive or

dominant alleles)

Angelman syndrome

Cystic Fibrosis

Huntington’s Disease

PKUSickle-cell traitTay-Sachs

Chromosomal (an extra

chromosome)Down syndrome

Autosomal Disorders

Genetic research

• Uses recombinant DNA technology to reconstruct cells and genes

Gene therapies

• Involve reinserting genetically-altered cells into a person

In vivo gene therapy

• Removes some viral genes, inserts cloned normal genes and reintroduces retrovirus to patient

Genetic Research

Description of different types of genetic testing:

http://www.youtube.com/watch?v=dJuo937gz44

Video Clip

BBC documentary on Designer Babies with commentary by Princeton professor Lee Silver:http://www.youtube.com/watch?v=TN9ep4B9Hw0&feature=PlayList&p=C7E239A945F4C4BA&playnext=1&playnext_from=PL&index=56

Video Clip

Behavior genetics

Tries to understand the genetic origins of behaviors

Incorporates the view that complex traits are determined by interaction of heredity and environment

Looks at statistical correlation, or concordance, of similar characteristics with genes

What is a concordance rate? Let’s find out.

Behavior Genetics

Concordance rates form the basis of estimates of heritability, the proportion of a trait that is thought to result from genetic factors.

How are these estimates determined?

Behavior Genetics

Adoption Studies• Studies how

adopted children resemble their adoptive versus their biological parents

Twin Studies• Compares

identical twins for traits thought to be heritable

• Hard to interpret because no twin’s environment is identical, even within same home

Behavior Genetics Studies

Basic Processes that Affect Behavior

• Habituation

• Classical Conditioning

• Operant Conditioning

• Social Learning

Environmental Influences and Contexts

A Typical Classical Conditioning Procedure

Operant Conditioning

Reinforcers increase the likelihood that a behavior will be repeated

Punishments decrease the probability that a behavior will be repeated

Applied Behavior Analysis

Application of learning principles to change behavior

Sometimes called behavior modification

Applied behavior analysis

Family systems are at heart of human behavior

Families pay critical role in orienting people to society and culture

Siblings share many similar experiences, but non-shared experiences and relationships also exist

Family and Culture

Stop and Think!

Your textbook suggests it is important to avoid ethnocentrism.

Do you agree? Why? Why not?

Cultural factors affect a cohort, a group of individuals born during the same historical era.

How would you describe YOUR cohort?

Sociocultural Influences

Types of cultural influences

Normative age-graded: biological and social changes

Normative history-graded: historical events such as wars, depressions, and epidemics

Non-normative: individual factors such as divorce, unemployment, illness, career changes

Sociocultural Influences

A Lifespan Profile on Influences

Lifespan development is a complex interaction

among several

important factors

Mediating factors—gender,

ethnicity, socioeconomic background—determine how

broader cultural-historical forces

will be experienced

The family will shape

one’s experience

in important

ways

Each person’s unique

personal characteristics will determine how they act in and adapt to the broader

context in which life unfolds

Development in a Broad Context