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Copyright © 2010 Pearson Education, Inc. All rights reserved.
Heredity and Environment
Chapter 2
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
Copyright © 2010 Pearson Education, Inc. All rights reserved.
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
Copyright © 2010 Pearson Education, Inc. All rights reserved.
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
• 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 genetically-altered 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
Copyright © 2010 Pearson Education, Inc. All rights reserved.
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
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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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Copyright © 2010 Pearson Education, Inc. All rights reserved.
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