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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