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

Chapter 2

2


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


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


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.


Computer Simulated DNA Molecule


Segment of DNA Visualized as a Ladder


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



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


Human Karyotypes


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


Comparison of Mitosis and Meiosis


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


Examples of Dominant-Recessive Gene Combinations


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


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


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)


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


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


Video Clip

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


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


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


Environmental Influences and Contexts

• Basic Processes that Affect Behavior

– Habituation

– Classical Conditioning

– Operant Conditioning

– Social Learning


A Typical Classical Conditioning Procedure


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


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



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


A Lifespan Profile on Influences


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


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


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


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