1. GENES, ENVIRONMENT, AND DEVELOPMENT
CHAPTER 3
GENES, ENVIRONMENT, AND DEVELOPMENT

2. Learning Objective
What do evolution and species heredity contribute to our understanding of universal patterns of development?

3. Species Heredity
Genetic endowment that members of a species have in common
Reason that certain patterns of development and aging are universal
Examples
Walk and talk around 1 year of age
Sexual maturation from 12-14
Wrinkling of skin in 40s and 50s

4. Darwin’s Theory of Evolution
Species heredity explained by evolutionary theory
Main arguments of Darwin’s theory
There is genetic variation in a species
Some genes aid adaptation more than others do
Adaptive genes passed on more frequently
Evolution is about the interaction between genes and environment

5. Modern Evolutionary Perspectives
Human development influenced by a shared species heredity that evolved through natural selection
Human development also influenced by cultural evolution
Humans inherit a characteristically human environment and learn methods of adapting to the environment
Cultural evolution is based on learning and socialization

6. Learning Objectives
What are the basic elements and processes of individual heredity, including genes, chromosomes, formation of a zygote, mitosis, and meiosis?
What has the Human Genome Project contributed to our understanding of human development?

7. Individual Heredity – The Genetic Code
Conception – new cell nucleus formed from genetic material of ovum and genetic material of sperm
New cell is the zygote
Each parent contributes 23 chromosomes, 46 total, organized into 23 pairs
Chromosomes - threadlike bodies in nucleus of each cell made up of genes

8. Individual Heredity – The Genetic Code
Sperm and ova each have only 23 chromosomes because they are produced through the cell division process of meiosis
A reproductive cell (in ovary or in testis) splits to form two 46-chromosome cells
The two cells split again to form a total of four cells, each of which receives 23 chromosomes
In the female, results in three nonfunctional cells and one ovum
In the male, results in four sperm

9. Individual Heredity – The Genetic Code
The single-cell zygote becomes a multiple-cell organism through the process of mitosis
A cell (and each of its 46 chromosomes) divides to produce two identical cells, each containing the same 46 chromosomes
Following conception, through mitosis, the zygote divides into two cells, then into four cells, then into eight cells, etc.
Mitosis continues throughout life

10. Individual Heredity – The Genetic Code
Except for ova and sperm, all normal human cells contain copies of the 46 chromosomes received at conception
Both members of a chromosome pair influence the same characteristics
Chromosomes are strands of DNA
Deoxyribonucleic acid made up of sequences of adenine, cytosine, guanine, and thymine (A, C, G, and T)
Sequences are functional units - genes

11. The Human Genome Project
Researchers mapped the sequence of the chemical units (A,C,G, and T) that make up the strands of DNA in a full set of human chromosomes
Human genome consists of genes that serve as a template for the production of particular proteins and DNA that regulates the activity of the protein-producing genes
999 of 1,000 base chemicals are identical; only 1 of 1,000 accounts for human differences

12. Learning Objectives
What factors account for genetic uniqueness?
How genetically similar are twins?
How is sex determined?

13. Genetic Uniqueness and Relatedness
Genetic uniqueness of children of same parents due to crossing over, an aspect of meiosis
Before separation, pairs of chromosomes line up; when they cross each other, parts are exchanged
Crossing over increases the number of distinct sperm or ova an individual can produce

14. Genetic Uniqueness and Relatedness
Genetic similarity of parent and child
An individual receives half her chromosomes and genes from her mother and half from her father
Genetic similarity of siblings
Siblings receive half their genes from the same mother and half from the same father, but meiosis determines the genes actually received
Siblings share half their genes, on average

15. Genetic Uniqueness and Relatedness
Identical twins or monozygotic twins (or identical triplets, etc.)
Genetically the same
Result when one fertilized ovum divides to form two or more genetically identical individuals
Fraternal twins or dizygotic twins
Result from release of two ova and fertilization by two sperm
As genetically alike as siblings

16. Determination of Sex Of the 23 pairs of chromosomes
22 pairs - autosomes
23rd pair - sex chromosomes
In males, the 23rd pair consists of a long chromosome (X) and a short chromosome with fewer genes (Y)
Females have two X chromosomes
Fathers determine a child’s sex
If a sperm carries a Y chromosome, the XY zygote is a genetic male
If a sperm carries an X chromosome, the XX zygote is a genetic female

17. Caption: Chromosomes in each cell consist of strands of DNA

18. Learning Objective
How are genes translated into physical and psychological characteristics?

19. Translation and Expression of the Genetic Code
Environmental influences combine with genetic influences to determine how a genotype is translated into a phenotype
Genotype
The genetic makeup a person inherits
Phenotype
The characteristics or traits that are expressed
Gene expression
Activation of particular genes in particular cells at particular times; guided by genetic influences and affected by environmental factors

20. Learning Objectives
What are the mechanisms by which traits are passed from parents to offspring?
What is an example of how a child could inherit a trait through each of these three mechanisms?

21. Mechanisms of Inheritance: Single Gene-Pair Inheritance
Pattern described by Gregor Mendel
Human characteristics influenced by one pair of genes (one from mother, one from father)
A dominant gene trait will be expressed
A recessive gene trait will be expressed only when the gene is paired with another recessive gene for the trait
Single gene-pair inheritance
Pattern described by Gregor Mendel
Human characteristics influenced by one pair of genes (one from mother, one from father)
A dominant gene trait will be expressed.
A recessive gene trait will be expressed only when the gene is paired another recessive gene for the trait.
In some cases, a dominant gene incompletely dominates a recessive partner gene and the result is a new trait that blends the parents’ traits –
Called incomplete dominance
Examples:
-crossing red and white flowers produces pink ones
-dark-skinned and light-skinned parents have a child with light brown skin
In other cases, two genes influence a trait but each is expressed in the product, as when crossing red and white flowers produces flowers with red and white streaks
Called codominance
Example:
an AB blood type is a mix of A and B blood types

22. Caption: Can you curl your tongue?

24. Mechanisms of Inheritance: Sex-Linked Inheritance
Sex-linked characteristics are influenced by single genes located on sex chromosomes
Actually X-linked because most attributes are associated with genes on the X
Y chromosomes are smaller and have fewer genes to serve as counterpart or to dominate
Example: if a boy inherits a recessive color-blindness gene on the X, there is no color vision gene on the Y to dominate the color-blindness gene

25. Mechanisms of Inheritance: Sex-Linked Inheritance
A female who inherits a color-blindness gene usually has a normal color-vision gene on her other X chromosome that can dominate the color-blindness gene
If a female is to be color-blind, she must inherit the gene on both Xs
Hemophilia is another condition that illustrates the principles of sex-linked inheritance

26. Caption: X-linked inheritance

27. Mechanisms of Inheritance: Polygenic Inheritance
Traits such as height, weight, intelligence, personality, and susceptibility to cancer and depression are polygenic
Influenced by multiple pairs of genes interaction with environmental factors
Many degrees of expression are possible in polygenic traits
Traits tend to be distributed in the population according to the normal curve

28. Learning Objectives
How do genetic mutations occur?
How do mutations affect development?
What are the most common chromosomal abnormalities?
When chromosomal abnormalities occur, how do they affect development?

29. Example: sickle-cell disease Can be inherited by offspring
Mutations
Mutation
A change in gene structure or arrangement that produces a new phenotype
May be harmful or beneficial depending on their nature and the environment
Example: sickle-cell disease
Can be inherited by offspring
Mutation
A change in gene structure or arrangement that produces a new phenotype
-Environmental hazards (radiation and toxic industrial waste) increase the likelihood of mutations
-However, most mutations are just spontaneous errors in cell division
May be harmful or beneficial depending on their nature and the environment
Example: sickle-cell disease
--Sickle-cell disease is a blood disease common among African Americans in which red blood cells take on a sickle shape.
It probably arose as a mutation but became more prevalent in Africa, Central America, and other tropical areas over many generations because having one of the recessive sickle-cell genes protected people from malaria and allowed them to live longer and produce more children than people without the protective gene.
Unfortunately, the sickle-cell gene does more harm than good where malaria is no longer a problem; carriers of the gene can be affected by some of the pain and difficulty breathing that affects individuals with sickle-cell disease.

30. Chromosomal Abnormalities
Chromosomal abnormalities occur when there are errors in chromosome division during meiosis
The ovum or sperm will have too many or too few chromosomes
Chromosomal abnormalities are the main source of pregnancy loss

31. Examples of Chromosomal Abnormalities
Down syndrome or trisomy 21
21st chromosomes = 3
Children have distinctive physical characteristics and typically are classified as having some degree of mental retardation
Associated with older age of parents
Down Syndrome or trisomy 21
21st chromosomes = 3
-Children have distinctive physical characteristics and typically are classified as having some degree of mental retardation.
--Distinctive eyelid folds, short stubby limbs, and thick tongues.
--Levels of intellectual functioning vary widely, but they are typically classified as having some degree of mental retardation and therefore develop and learn at a slower pace than most children
-In the United States and other wealthy nations, many people with Down syndrome are now living into middle age, when many of them develop signs of premature aging, including Alzheimer’s disease
-Associated with older age of parents

32. Examples of Chromosomal Abnormalities
Chromosomal abnormalities that involve a child receiving too few or too many sex chromosomes
Consequence of errors in meiosis or damage from environmental hazards
Turner syndrome – a female born with a single X chromosome (XO)
Klinefelter syndrome – a male born with one or more extra X chromosomes (XXY)
Fragile X – one arm of the X is only barely connected
Chromosomal abnormalities that involve a child receiving too few or too many sex chromosomes
Consequence of errors in meiosis or damage from environmental hazards
Turner Syndrome – a female is born with a single X chromosome (XO)
--Incidence is about 1 in 3000
--Girls remain small and often have stubby fingers and toes, a “webbed” neck, and underdeveloped breasts.
--They are unable to reproduce, typically favor traditionally feminine activities
--Often have lower-than-average spatial and mathematical reasoning abilities
Klinefelter syndrome – a male is born with one or more extra X chromosomes (XXY)
--Incidence is approximately 1 in 200
--Klinefelter males tend to be tall and generally masculine in appearance
--They are sterile and at puberty develop feminine sex characteristics such as enlarged breasts.
--Most have normal intelligence test scores, but many are below average in language skills and school achievement
Fragile X – one arm of the X is only barely connected (hence the term fragile).
--It is the most common hereditary cause of mental retardation
--Fragile X syndrome causes mental retardation or some degree of cognitive impairment in most affected persons and autism in some as well.
The condition is usually not diagnosable until around age 3 unless parents know that fragile X runs in the family and ask for genetic testing.

33. Caption: Photo of X chromosome with fragile X problem

34. Learning Objectives
What methods are used to screen for genetic abnormalities?
What are the advantages and disadvantages of using such techniques to test for prenatal problems?
What are some abnormalities that can currently be detected with genetic screening?

35. Genetic Diagnosis and Counseling
Genetic counseling
A service that helps people understand and adapt to the implications of genetic contributions to disease
Carriers do not have the disease but can transmit the gene for it to their children

37. Issues in Genetic Diagnosis and Counseling
Sickle-cell disease
Sickle-shaped blood cells cluster together and distribute less oxygen through the circulatory system
If parents are carriers of the recessive gene for sickle-cell disease
Have 25% chance of having a child with sickle-cell disease
Have a 50% chance of having a child who will be a carrier

38. Issues in Genetic Diagnosis and Counseling
Huntington’s disease
Associated with a single dominant gene
Strikes in middle age and disrupts the nervous system
Child of a parent with Huntington’s disease has a 50% chance of developing the disease
Discovery of gene for Huntington’s on chromosome 4 led to a test that can reveal if a person has inherited the gene

39. Learning Objectives
What methods do scientists use to discern the contributions of heredity and environment to physical and psychological traits?
What are the strengths and weaknesses of these methods?
How do scientists estimate the influences of heredity and environment to individual differences in traits?
How do genes, shared environment, and nonshared environment contribute to individual differences in traits?

40. Genetic and Environmental Influences: Behavioral Genetics
Study of the extent to which genetic and environmental differences contribute to differences in traits
Use heritability estimates
The proportion of all the variability in the trait within a large sample that can be linked to genetic differences among individuals
Variability that is not associated with genetic differences is associated with environmental and experiential differences

42. Studying Genetic and Environmental Influences: Experimental Breeding
Selective breeding
Attempting to breed animals for a particular trait to determine whether the trait is heritable
Tryon bred maze-bright rats to demonstrate the influence of genetics upon maze-learning ability
Other animal breeding studies showed genetic contributions to activity level, emotionality, aggressiveness, etc.

43. Studying Genetic and Environmental Influences: Twin, Adoption, and Family Studies
Twin studies
Studies of twins, both identical and fraternal, reared apart and together
Adoption studies
Are adopted children more similar to biological parents or to adoptive parents?
Family studies
Studies of siblings with different degrees of genetic similarity and varying environments

44. Estimating Influences
Concordance rates
Statistical calculations to estimate the degree to which heredity and environment account for individual differences in a trait of interest
A trait is heritable if the concordance rates are higher for more genetically related than for less genetically related pairs of people
Correlation coefficients
Used when a trait (e.g., intelligence) can be present in varying degrees

45. Estimating Influences
From correlations reflecting the degree of similarity between twins, behavioral geneticists can estimate the contributions to individual differences in emotionality from
Genes
Shared environmental influences
Common experiences
Nonshared environmental influences
Experiences unique to the individual

46. Molecular Genetics
Analysis of genes and their effects
Useful in identifying the multiple genes that contribute to polygenic traits
Example: Alzheimer’s disease
Twin studies show heritability but the roles of specific genes have not been clarified

47. Learning Objectives
How do genes and environments contribute to individual differences in intellectual abilities, personality and temperament, and psychological disorders?
What do researchers mean when they talk about the heritability of traits?
Which traits are more strongly heritable than others?

48. Findings from Behavioral Genetics Research – IQ
Correlations highest in identical twins
Heritability of IQ is about .50
Genetic differences account for 50% of variation in IQ and environmental differences for 50%
Genetic endowment appears to gain importance from infancy to adulthood as a source of individual differences in IQ
Shared environmental differences become less significant with age

49. Findings from Behavioral Genetics Research – Temperament and Personality
Tendencies to respond in predictable ways that serve as the building blocks of personality
Buss and Plomin (1984) reported average correlations of between temperament scores of identical twins but scores for fraternal twins not much greater than zero
Conclusion: living in the same home does not generally make children more similar in personality
Shared environment influences are important but nonshared influences are more important

50. Findings from Behavioral Genetics Research – Psychological Disorders
Schizophrenia
Concordance rate for schizophrenia in identical twin pairs is 48% and for fraternal twins the rate is 17%
90% of children who have one parent with schizophrenia do not develop schizophrenia
This means that environmental factors contribute significantly
People inherit predispositions to develop disorders, not the disorder per se

52. Heritability of Different Traits
Traits that are strongly heritable include
Physical characteristics – eye color, height, weight
Physiological functions – measured brain activity, reactions to alcohol, level of physical activity, susceptibility to certain diseases
A trait that is moderately heritable
General intelligence
Traits that are less heritable
Aspects of temperament and personality, susceptibility to many psychological disorders

53. Influences on Heritability Estimates
Characteristics of the sample studied
Age, environmental factors
Environmental factors
Socioeconomic status

54. Caption: Correlations between the traits of identical twin raised apart in to Minnesota Twin Study

55. Learning Objectives
What is an example that illustrates the concept of a gene-environment interaction?
What are three ways that genes and environments correlate to influence behavior?
What are the major controversies surrounding genetic research?

56. Gene-Environment Interactions
The effects of genes depend upon the nature of the environment and how the individual responds to the environment
Often takes a combination of high-risk genes and high-risk environment to trigger psychological problems

57. Gene-Environment Correlations
Three kinds of gene-environment correlations
Passive – the home environment that parents provide their children is correlated with the children’s genotypes
Evocative gene-environment correlations
Child’s genotype evokes certain types of reactions from others
Active gene-environment correlations
Children’s genotypes influence the kinds of environments they seek
Three kinds of gene-environment correlations
-Passive – the home environment that parents provide their children is correlated with the children’s genotypes
--Example: Sociable parents not only transmit their “sociable” genes to their children but also, because they have “sociable” genes, create a social home environment—inviting their friends over frequently, taking their children to many social events, and so on. The combination of genes for sociability and a social environment may make them more sociable than they would otherwise be.
--Example: By contrast, the child with shy parents may receive genes for shyness and a correlated environment without much social stimulation.
Evocative gene-environment correlations
-Child’s genotype evokes certain types of reactions from others
-A child’s genetic makeup may affect the reactions of other people to a child and, hence, the kind of social environment that the child will experience.
--Example: a smiley, sociable baby is likely to get more smiles, hugs, and social stimulation than the wary, shy baby—more opportunities to build social skills.
--Example: The sociable child may be chosen more often as a playmate by other children, the sociable adolescent may be invited to more parties, and the sociable adult may be given more job assignments involving public relations.
Active gene-environment correlations
Children’s genotypes influence the kinds of environments they seek
--Example: The individual with a genetic predisposition to be extraverted is likely to go to every party in sight, invite friends to the house, join organizations, and otherwise build a “niche” that is highly socially stimulating and that strengthens social skills.
--Example: The child with genes for shyness may actively avoid large group activities and instead develop solitary interests.

58. Genetic Influences on Environment
Notion that people’s genes are correlated with and possibly influence their life experiences
Measures of environment are heritable
Especially family environments of children
Evidence that those who have closest genetic similarity are also similar in the environments they experience and in their perceptions of those environments

59. Controversies Surrounding Genetic Research
Accomplishments in the study of genetics have led to debates about procedures, public policy, and ethical issues
Reproductive technology, cloning, gene therapy, stem cell research
Some researchers may have overstated the importance of genes and underestimated the importance of family in development