heredity and environment


Chapter 2



Heredity and Environment

Molecular Genetics

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 genesdelineated pieces of DNA

There are about 25,000 genes in human body

Major Features of a

Typical Cell

Computer-Generated Stimulation of

DNA Molecule

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.

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

According to the Human Genome

Project, all humans are 99.9% genetically identical.

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

• Order of pairing is important

What Is Protein Synthesis?

Most significant thing genes do is build proteins

Proteins are molecules that control life

Over 200,000 different proteins have been identified in humans

Common Proteins and Their Functions in the Human Body

Genes, Chromosomes, and Cell


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


’s chromosomal makeup can be visualized in karyotypes

Human Karyotypes

Cell Division and Reproduction

Comparison of Mitosis and Meiosis

From Genotype to Phenotype


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

• Dominant allele

• Recessive allele

• Dominant trait expression

• Recessive trait expression

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

Genetic Inheritance

Polygenic human characteristics

• Determined by more than one gene pair

Sex-linked traits

• Usually passed on by

X chromosome

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

Genetic Inheritance

Genetic mutations

• May occur during mitosis or meiosis when

DNA molecule is altered during cell division

• May be beneficial or detrimental

Genetic and Chromosomal Disorders

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

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

Epigenetic modifications may be transmitted to next generation via genetic inheritance

Gene-environment interactions occur at many levels

Experience in life can have dramatic effect on later developmental outcomes

Some Sex-Linked Disorders

Autosomal Disorders

Genetic Research

Genetic research

• Uses recombinant

DNA technology to reconstruct cells and genes

Gene therapies

• Involve reinserting geneticallyaltered cells into a person

In vivo gene therapy

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

Video Clip

Description of different types of genetic testing:

Video Clip

BBC documentary on Designer Babies with commentary by Princeton professor Lee

Silver: feature=PlayList&p=C7E239A945F4C4BA&playne xt=1&playnext_from=PL&index=56

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 Studies

Environmental Influences and Contexts


Processes that Affect


• Habituation

• Classical


• Operant


• Social


A Typical Classical Conditioning


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

Applied behavior analysis

Application of learning principles to change behavior

Sometimes called behavior modification

Family and Culture

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 nonshared experiences and relationships also exist

Stop and Think!

Your textbook suggests it is important to avoid ethnocentrism.

Do you agree? Why? Why not?

Sociocultural Influences

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

A Lifespan Profile on Influences

Development in a Broad Context