Download Heredity and Environment

2
Heredity
and Environment
Chapter 2
Copyright © 2010 Pearson Education, Inc. All rights reserved.
Heredity and Environment
• Molecular Genetics
• Genes, Chromosomes, and Cell Division
• Genetic and Chromosomal Disorders
• Behavior Genetics
• Environmental Influences and Contexts
• Environment in a Broader Context: Family and
Culture
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Molecular Genetics
• Genetic instructions are found in the DNA
molecules found in the nucleus of each cell
• DNA is a complex molecule made up of
nucleotides and four different bases.
• The bases form base pairs that should not vary
• The basic units of inheritance are genes, which
are delineated pieces of DNA.
• There are about 25,000 genes in the human
body
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A Cell of the Human Body
SOURCE: Figure “A bodily cell,” In M. R. Cummings (Ed.), Human heredity: Principles and issues (4th ed., p. 16). Pacific Grove, CA:
Books/Cole. Copyright ｩ 1997. Reprinted with permission of Wadsworth, an imprint of the Wadsworth Group, a division of Thomson
Learning. Fax 800-730-2215.
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Computer Simulated DNA Molecule
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Segment of DNA Visualized as a Ladder
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Protein Synthesis
• The most significant thing genes do is
build proteins
• Proteins are the molecules that control life
• Over 200,000 different proteins have been
identified in humans
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Copyright © 2010 Pearson Education, Inc. All rights reserved.
Genes, Chromosomes, and Cell
Division
• When a cell divides, the 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
• The 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
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Human Karyotypes
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Cell Division and Reproduction
• Cells divide in a process called mitosis, which
creates two cells with identical sets of
chromosomes
• Meiosis is the cell division process that produces
ova and sperm, each of which contain one half
of the full set of chromosomes
• The genotype refers to the genes an individual
inherits
• Genes, like chromosomes, exist in pairs, each
half of which is an allele
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Comparison of Mitosis and
Meiosis
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From Genotype to Phenotype
• All of a person’s pairs of alleles form the
person’s genotype, or genetic code
• Some alleles are dominant over others, for
instance the allele for brown eyes
• Others are recessive, such as the allele for blue
eyes
• Two recessive alleles are needed to express a
recessive trait
• But it only takes one dominant allele for a
dominant trait to be expressed
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Examples of Dominant-Recessive
Gene Combinations
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Genetic Inheritance
• Nearly all human characteristics are polygenic:
determined by more than one gene pair
• Some traits are sex-linked, usually passed on by
the X chromosome
– Since men have only one “X,” they are at risk for traits
associated with the X chromosome
• Genetic mutations may occur during mitosis or
meiosis, when the DNA molecule is altered
during cell division
• Mutations may be beneficial or detrimental
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Genetic and Chromosomal
Disorders
• About 3% are born with congenital anomalies, or
birth defects
• Genetic anomalies involve problems with the
instructional mechanism of the genetic process
• Sex-linked disorders can occur when the
gametes do not replicate correctly or when
genetic information, even entire chromosomes,
are missing or duplicated
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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)
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Autosomal Disorders
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•
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•
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•
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Genetic (recessive or dominant alleles)
Angelman syndrome
Cystic Fibrosis
Huntington’s Disease
PKU
Sickle-cell trait
Tay-Sachs
Chromosomal (an extra chromosome)
Down syndrome
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Genetic Research
• Uses recombinant DNA technology to
reconstruct cells and genes
• Gene therapies involve reinserting geneticallyaltered cells into a person
– Used to produce a variety of proteins, such as insulin
• In vivo gene therapy removes some viral genes,
inserts cloned normal genes, and retrovirus is
reintroduced to patient
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Video Clip
Description of different types of genetic
testing:
http://www.youtube.com/watch?v=dJuo937gz44
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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&playne
xt=1&playnext_from=PL&index=56
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Behavior Genetics
• Behavior genetics tries to understand the genetic origins
of behaviors
• Incorporates the view that complex traits are determined
by an interaction of heredity and environment
• Behavioral genetics looks at the statistical correlation, or
concordance, of similar characteristics with genes
• Concordance rates form the basis of estimates of
heritability, the proportion of a trait that is thought to
result from genetic factors
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Behavior Genetics Studies
• 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
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Environmental Influences
and Contexts
• Basic Processes that Affect Behavior
– Habituation
– Classical Conditioning
– Operant Conditioning
– Social Learning
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A Typical Classical Conditioning
Procedure
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Operant Conditioning
• Reinforcers increase the likelihood that a
behavior will be repeated
– Example: A child is given a delicious cookie
after saying “please” and becomes more likely
to say “please” in the future.
• Punishments decrease the probability
that a behavior will be repeated
– Example: A child who misbehaves is scolded
and becomes less likely to misbehave in the
future
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Family and Culture
• Family systems are at the heart of human behavior
• Siblings share many similar experiences, but
nonshared experiences and relationships also exist
• Families pay a critical role in orienting him or her to
society and culture
• It is important to avoid ethnocentrism, the tendency
to assume that our own beliefs, customs, and values
are normal and others are abnormal
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Sociocultural Influences
• Cultural factors affect a cohort, a group of
individuals born during the same historical era
• There different 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
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A Lifespan Profile on Influences
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Development in a Broad Context
• 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
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Summary
• Genetic instructions are contained in the DNA molecules
found in the nucleus of each of our cells.
• The basic unit of inheritance is the gene; genes are units
of DNA molecules
• The cells are arranged in chromosomes, and we have 23
pairs of chromosomes in each cell
• Genotype refers to what our genes are, but phenotype
refers to what we actually express, or look like
• Most human characteristics are caused by more than
one pair of genes
• Some genes are dominant, some recessive
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Summary
• Genetic and chromosomal disorders may cause birth
defects and other problems, such as spontaneous
abortions
• Genetic tests today allow prospective parents to learn if
their baby might have genetic defects. Through genetic
counseling they can assess the risk of carrying the baby
to term
• Behavior genetics studies how genes impact human
behavior
• But human behavior is never caused by genes alone,
rather there are complex interactions between our genes
and the environment
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Summary
• Environmental influences on our genes can be very
specific events in our individual lives, or they can occur
broadly across cultures
• Learning is one of the primary environmental factors that
shape our development. Major forms of learning include:
• Classical and operant conditioning
• Social learning
• All development takes place in the broader context of
family and culture
• Thus, hereditary and environmental forces continually
interact as development unfolds
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