Meiosis: This is division of the germ cells (i.e., the male or female reproductive cells); the result is that, for a male, the sperm cells contain half the number of chromosomes (N=23) that normal cells in other parts of the body contain (N=46). Meiosis results in sperm (or egg) cells that are a more or less random collection of one each of the chromosomes from Mom and Dad;
Meiosis for a male:
His germ cells start out with 23 pairs of chromosomes, one set from mom (m) and one set from dad (d) as depicted on the left:
After Meiosis
Mom Dad Sperm#1 Sperm#2 Sperm #3 Sperm #4 . . .
1 m d m d mc dc
2 m d d mc m dc
3 m d dc m c mc
4 m d
5 m d
6 m d
7 m d
8 m d
9 m d
10 m d
11 m d
12 m d
13 m d
13 m d
14 m d
15 m d
16 m d
17 m d
18 m d
20 m d
21 m d
22 m d
23 X Y X Y Y X
The figure includes crossover: half of the m and d chromosomes interchange genetic material with each other. These are indicated by mc and dc respectively. The female germ cell undergoes a similar process, so the actual number of possible genetic combinations between one man and one woman is staggeringly high.
mitosis: Normal cell division in non-germ cells. This replicates the previous cell unless there are errors.
autosomes: The 22 paired non-sex chromosomes.
allele: An alternate form of a gene. Alleles occur at loci on chromosomes.
If the alleles are homozygous, the two genes at the locus are the same.
If the alleles are heterozygous, the two genes at the locus are different.
codominant: Both alleles at a locus are expressed with equal force; e.g., the ABO blood system: If you are AB, you express both alleles
dominant: Only one allele at a locus is expressed. The other (recessive gene) is suppressed.
recessive: An allele that is suppressed in the presence of a dominant gene. If the two recessive alleles occur at a locus, then the trait is expressed.
sex chromosomes: The 23rd pair of chromosomes determine sex: Males are XY and females are XX. Non-sex chromosomes are autosomes
X-linkage: Genes carried on the X-chromosome. Since males only have one X chromosome, any recessive gene on the X-chromosome will be expressed in males. In females, such recessive genes may be suppressed by a dominant gene on her other X-chromosome. It is important to understand x-linkage and how it works so that you understand why males are prone to disorders caused by recessive genes on the X chromosome. Understand Hemophilia as an X-linked disorder.
modifier genes: genes that influence a trait indirectly. For example, a dominant gene affects whether people can get early cataracts, but modifier genes determine how serious the cataracts are likely to be. Often these modifier genes are located on different chromosome.
Genes work together. Most traits studied by psychologists are influenced by multiple genes (polygeny) and most genes influence more than one trait (pleiotropy).
Recessive genes are hard to get rid of, even if they are highly deleterious or even lethal. That's because they are typically masked by dominant genes. Even if both parents are recessive for a harmful gene like PKU, only 25% of their offspring would be homozygous for the trait.
What would the above figure look like if only the mother was a carrier? (You'll have to come to class to see it.) What would it look like if one parent was homozygous for the recessive gene? What would happen to all of this if PKU was dominant instead of recessive? In fact, some disorders are caused by dominant genes. Huntington's chorea is a lethal gene, but it's effects don't show up until age 35-40. Why would this type of lethal gene survive in the population?
Some recessives are actually beneficial if the person is heterozygous for the condition. The example for the latter is Sickle Cell Anemia. Sickle Cell Anemia benefits people living in areas infested by malaria. Heterozygotes are superior to either homozygous condition.
Chromosomal disorders: Down syndrome is caused by non-disjunction of the 21st chromosome during meiosis. As a result, the child has three 21st chromosomes instead of the normal two. Down Syndrome is a genetic disorder but it is not caused by having a harmful gene. These are children with Down's Syndrome:
This is what the karyotype looks like:
Behavior genetics challenges the behaviorist perspective of John Watson who famously wrote:
"Give me a dozen healthy infants, well-formed, and my own specific world to bring them up in and I'll guarantee to take any one at random and train him to become any type of specialist I might select -- a doctor, lawyer, artist, merchant-chief and, yes, even into beggar-man and thief, regardless of his talents, penchants, tendencies, abilities, vocations and race of his ancestors."
1.) BEHAVIOR GENETICS STUDIES IDIOGRAPHIC DEVELOPMENT:
2.) BASIC CONCEPTS:
PHENOTYPE = OBSERVABLE OR MEASURABLE CHARACTERISTICS (E. G.,
HAIR COLOR, IQ)
GENOTYPE = GENETIC COMPLEMENT OF PERSON (E.
G., HAVING A
RECESSIVE GENE FOR COLOR BLINDNESS)
POLYGENY: MANY GENES INFLUENCE A TRAIT BUT
NO ONE GENE HAS A
MAJOR EFFECT (E. G., HUNDREDS OF GENES INFLUENCE IQ AND
PERSONALITY);
BEHAVIOR GENETIC CONCEPTS
GENOTYPE -- ENVIRONMENT INTERACTIONS: WAYS THAT GENETIC TENDENCIES BECOME CORRELATED WITH PARTICULAR ENVIRONMENTS.
1.) ACTIVE GENOTYPE -- ENVIRONMENT INTERACTION (NICHE-PICKING):
CHILD SEEKS OUT ENVIRONMENTS AS A RESULT OF GENETIC INFLUENCES (E. G., CHILD WITH A SENSATION SEEKING TEMPERAMENT)
The active genotype-environment interaction probably increases in importance as the child grows older. Why?
2.) EVOCATIVE GENOTYPE-ENVIRONMENT
INTERACTION: CHILD EVOKES
ENVIRONMENTS AS A RESULT OF GENETIC INFLUENCES (E. G., CHILD WITH A DIFFICULT
TEMPERAMENT EVOKES NEGATIVE RESPONSES IN CAREGIVERS; CHILD WITH A SUNNY
DISPOSITION GETS POSITIVE RESPONSES.)
Another example: Children with violent natural parents and children with
non-violent natural parents are adopted into separate families, and the adoptive
families are compared. Children with violent natural parents have adoptive
parents who use harsh discipline. Children with non-violent natural parents have
adoptive parents who use mild discipline. This "environmental" effect is the
result of an evocative genotype--environment effect: Aggressive, difficult
children evoke harsh parenting.
3.) PASSIVE GENOTYPE -- ENVIRONMENT INTERACTION: CHILD IS PASSIVE RECIPIENT OF ENVIRONMENTS WHICH FIT WITH HIS/HER GENOTYPE. (E. G., INTELLIGENT PARENTS HAVE CHILD WITH GENETIC POTENTIAL FOR INTELLIGENCE; PARENTS ALSO PROVIDE A GREAT DEAL OF INTELLECTUAL STIMULATION WHICH MESHES WITH THE CHILD'S GENETIC POTENTIAL)
SHARED ENVIRONMENTAL INFLUENCES:
ENVIRONMENTAL INFLUENCES
SHARED BY CHILDREN IN THE SAME FAMILY.
EXAMPLE: CHILDREN IN SAME FAMILY GO TO SAME SCHOOL, HAVE SAME
ALCOHOLIC MOTHER, ETC
UNSHARED ENVIRONMENTAL INFLUENCES:
DIFFERENT CHILDREN RECEIVE
DIFFERENT ENVIRONMENTS; OR DIFFERENT CHILDREN RESPOND TO THE
SAME ENVIRONMENT DIFFERENTLY;
EXAMPLE: DIFFERENT BIRTH ORDER, SEX DIFFERENCES
According to Plomin et al. (2001), unshared environmental influences are typically far more important than shared environmental influences. Notice that the unshared environment idea is linked to the active child concept and is used to explain the fact that adoptive siblings and even biologically related siblings are typically not very similar. As the text says, 'Clearly, researchers in individual differences can no longer assume a homogeneous home environment for all siblings; be alert to this fact when you read the reports and conclusions of such studies.'
Reaction Range: The range of phenotypic
expression depending on different
environments of different quality. Different people have different reaction
ranges; i.e.,
they respond differently to the same environments.
IQ score
_____________________________________________
Abusive Poor Average Enriched
Quality of Environment
CANALIZATION: THE GENETIC RESTRICTION OF A PHENOTYPE TO A SMALL NUMBER OF DEVELOPMENTAL OUTCOMES, PERMITTING ENVIRONMENTAL INFLUENCES TO PLAY ONLY A SMALL ROLE IN THESE OUTCOMES; In other words, genes restrict the extent to which the environment can influence the phenotype. A highly canalized phenotype is not much influenced by environmental influences; a weakly canalized phenotype is open to environmental influences.
Behavior Genetic Methods (Out of order)
Adoption Studies: Comparison of adopted children to natural and adoptive families. Correlations with natural family indicate genetic influence; correlations with adoptive family indicate environmental influences. Assumption: environment before adoption does not systematically affect the behavior studied.
Adopted children's IQ scores are correlated with those of their biological parents, indicating genetic influence. Their IQ scores are also correlated with their adoptive parents at age 7, indicating environmental influence. However, at age 18, there is no correlation between adopted children and their adoptive parents after 18 years of living together!!! Not on test: Notice that, again, as noted in Table 2-4 on p. 72, there is a distinction between beneficial effects of adoption on the average IQ of adoptees while nevertheless, the adoptees remain more highly correlated with their biological parents. Correlations are independent of the mean.
The findings of adoption studies are influenced by the range of the subject population. Researchers try to study children adopted into a wide range of environments so that they will not underestimate the effects of environmental differences. In general, a wider range, especially if it included abusive, highly stressful environments, would usually result in a lower estimate of genetic influences. Why?
Twin Studies:
Monozygotic (MZ) (identical) twins: Twins that share the same sperm and egg.
Dizygotic (DZ) (fraternal) twins: Twins that have different sperm and egg. Genetically they are no more alike than any other two siblings.
Environmental influences are indicated if MZ twins and DZ twins have about the same correlations for a trait. Genetic influences are indicated if MZ twins are substantially more similar than genetic twins.
Assumption: Environmental influences do not tend to make MZ twins more similar than DZ twins. (This would occur if parents treat MZ twins more similarly than DZ twins because, for example, it's cute to have them dress alike and if this procedure actually made their personalities or IQ more similar.) One way to get around this is to study MZ twins reared apart, especially if they are reared in radically different environments.
Table 2.5 Correlations for IQ scores
MZ twins reared together .86
MZ twins reared apart .79
DZ twins reared together .60
Siblings reared together: .47
Parent and Child: .40
Foster parent and child at age 7: .31 at age 18: 0.00
Siblings reared apart: .24
Cousins: .15
THE DEGREE OF GENETIC INFLUENCE INCREASES AS CHILDREN APPROACH ADULTHOOD; I.E. GENETIC INFLUENCES ARE STRONGER IN ADULTHOOD THAN AMONG CHILDREN.
1.) CORRELATIONS OF MZ TWINS STAY HIGH
WHILE
CORRELATIONS FOR DZ TWINS DECLINE
IQ CORRELATIONS FOR MZ AND DZ TWINS
AGE MZ DZ
6 MO .75 .72
12 MO .68 .63
24 MO .81 .73
36 MO .88 .79
4 YR .83 .71
6 YR .86 .59
8 YR .83 .66
15 YR .88 .54
2.) ADOPTION STUDIES
a.) CORRELATION BETWEEN ADOPTIVE PARENTS AND ADOPTED CHILDREN
DECLINES FROM .35 TO ZERO
AGE 7: r=0.35 AGE 17: r=0.00
b.) IQ OF ADOPTED CHILDREN DECLINES TO
CLOSE TO
THE IQ OF NATURAL PARENTS
AGE 7: IQ OF ADOPTED CHILDREN = 110
AGE 17: IQ OF ADOPTED CHILDREN = 95
EXPLANATION:
ACTIVE GENOTYPE--ENVIRONMENT CORRELATION (NICHE-PICKING)
BECOMES MORE IMPORTANT AS CHILDREN GET OLDER
CONCLUSION: DIFFERENT ENVIRONMENTS WITHIN
THE "NORMAL" OR
"AVERAGE" RANGE DO NOT HAVE MUCH INFLUENCE ON IQ.
HOWEVER, ABUSIVE ENVIRONMENTS CAN AND DO
AFFECT IQ.
AVERAGE VS ABUSIVE ENVIRONMENTS
IQ score
_____________________________________________
Abusive Poor Average Enriched
Quality of Environment
A recent study by Turkheimer suggests less heritability (genetic influence) at the lower end of the socioeconomic scale, and much higher heritability at the higher ends. The idea is that in better environments, the vast majority of variation is caused by genetic variation. But in poor environments, more variation is caused by bad environments. However, other studies have not found this effect except in clearly abusive environments.
Rank Order versus Average Effects of Adoption (textbook, p. 92):
One classic adoption study showed that adopted children often averaged 20 or more IQ points higher than their biological mothers. Because in this study the adoptive parents tended to be more highly educated and more socially and economically advantaged than the biological parents, this result was probably due to the more stimulating home environment that the adoptive parents provided. But note also that, despite this environmental influence on development, individual differences seemed still to be substantially influenced by genetic inheritance. The rank ordering of the children's IQ scores more closely resembled that of their biological mothers than that of their adoptive parents. The children whose biological mothers had the lowest IQ scores were likely to have lower IQ scores than the children whose biological mothers scored higher. Thus, although the absolute level of intellectual development was apparently boosted by the environmental influences provided by the adoptive parents, individual differences among the adopted children in intellectual performance--that is, their relative standings in this regard--appeared to stem more from their biological inheritance than from the increased intellectual stimulation provided in their adoptive homes.
THE FOLLOWING ADOPTION STUDY ILLUSTRATES THESE FINDINGS
NP = NATURAL PARENTS;
AP = ADOPTIVE PARENTS
AC = ADOPTIVE CHILDREN
CHILDREN ADOPTED NEAR BIRTH
120
111
115
129
125
AP: X= 120
114
112
110
108
106
AC: X = 110
94
92
90
88
86
NP: X = 90
TESTED AT AGE 7:
ENVIRONMENTAL VARIATION IS IMPORTANT:
AVERAGE OF AC (110) > AVERAGE OF NP (90); THIS IS AN AVERAGE EFFECT OF ADOPTION
OF 20 IQ POINTS. STUDIES TEND TO SHOW THAT THIS AVERAGE EFFECT WASHES OUT AS THE
CHILDREN APPROACH ADULTHOOD.
GENETIC VARIATION IS IMPORTANT:
1.) AVERAGE OF AC (110) < AVERAGE OF AP (120)
2.) POSITIVE CORRELATION BETWEEN AC AND NP
Psychologists agree that genetic variation and environmental variation both influence phenotype. Psychologists see "genetic endowment as to some extent constraining what a person can become and do." Interactions between genes and environment are often complex.
Gottlieb's bi-directional model, studied in Chapter 1, is now used as a model of genetic influences. This is akin to the systems theory approach: Everything affects everything else. Note that the environmental effects on the genes refer to turning the genes on or off, not to actually modifying the genes. For example, in the mallard duck, a 'genetically governed preference' for the sounds of other ducks is modified by exposing them to different sounds before they are born. The idea would be that a different gene would be turned on, not that the duck's genes are changed. A better example might be the effects of losing a competitive tennis match on testosterone. The loss is has an effect on behavior (slumping posture) and psychological state (low self-esteem), and there is lowered neural activity in certain parts of the brain; ultimately the genes for testosterone are turned off. But the genes haven't been changed by these events, and when the person later wins a match, the genes may turn on again.
The developmental stage of the child is relevant to whether the environment has
an influence; e.g., critical periods for the effects of teratogens on the fetus.
The point is that environmental influences are dependent on timing. Genetic
systems determine when the environment may have an influence.
PKU: Effects of dietary intervention on PKU depend on when the intervention is attempted. Earlier intervention is more effective. See Fig. 2-9 on p. 70.
Heritability factors: A statistical estimate of the contribution of genetic differences to phenotypic differences in traits, such as intelligence or personality. Traits with high heritability are mainly influenced by genetic differences: Most of the differences we see among people are the result of genetic differences. Low heritability is the opposite. Note that heritability may be different for different groups and under different environmental conditions. It may also change with age. (In general, genetic influence becomes stronger with age.) What would happen to heritability if everyone was raised in the same environment? (Hint, since there are no environmental differences, all of the differences in the population would be due to genetic differences. This means the heritability would be 1.00--all of the variation would be explainable by genetic differences between individuals.
(Not on test: Heritability is a proportion of the entire variation that is due to genetic variation and therefore ranges between 0 and 1. A heritability of 1 would mean that all of the variation is genetic, a heritability of 0 would mean that all the differences are caused by different environments. A heritability of .5 is common for many traits and means that about half of the variation is the result of people having different genes and about half is the result of their being in different environments.)
Psychologists value behavior genetics not just because it reveals genetic influences, but because it also tells us lots about environmental influences. By this the text is referring to things like passive, evocative, and active genetic influences on the environment and shared versus unshared environmental influences.
p. 72: Table 2-4: Of these points, note especially #2, #4, and #5:
#2: strong genetic effects do not rule out environmental influences. The point is difficult, and I won't ask you about it on the test, but notice that it is possible for there to be strong correlations between biological relatives for, say IQ (indicating relatively high heritability), but that children may still show a general rise in IQ levels as a result of adoption (indicating environmental influence).
#4: Genetic influences increase with age rather than decrease.
#5: Genes affect developmental change, and not all genes are present at birth: Many genes, like the genes for puberty and higher cognitive processing, are not turned on until later in development. People often think that all genetic influences must be observable at birth, but this is not true. Puberty, baby teeth, gray hair, and Piaget's stages are influenced by genes turning on and off during development.
Temperament
Temperament is a person's typical mode of response to the environment. It's really an early version of personality, and includes things like activity level, excitability, positive emotion, etc. Temperament is usually used in describing infants and young children, but it's linked to personality in adults. I may lecture about personality later in the course.
The work of Thomas and Chess is famous but mainly outdated. Most important is their idea of difficult temperament because some research has shown that this is a risk factor for later problems. Children with difficult temperament sleep and eat irregularly, are easily upset by new situations and experience extremes of fussiness and crying. See the vignette for Chris on p. 76 and top of p. 77. Easy babies are the opposite.
Rothbart's temperament components, listed in Table 2-6 (p. 77). (FFM dimension indicates the dimension of adult personality that is linked to this temperament trait. FFM = the Five Factor Model of personality.)
Positive affect: Smiling, laughter, etc. (FFM Extraversion)
Irritable distress: Irritability, fussiness or anger and distress at limitations on her behavior.
Fearful distress: indexed by negative reactions to new situations (FFM Neuroticism)
Activity level: Child's tendency to be more or less active.
Attention span/persistence: concentration, focus on task, distractibility (FFM Conscientiousness)
Rhythmicity: Predictability or regularity of child's behavior patterns.
Racial differences in temperament: Chinese, Japanese, American Indian babies are calmer, easier to console, more able to quiet themselves after quieting = better inhibitory ability. We shall see that this has ramifications for peer relations and school performance in later chapters.
Difficult infants tend to have more behavioral problems later, including conduct
disorder (aggressiveness), and poor school performance. This could be for two
reasons: (1) characteristics of the child (malleability); (2) the responses such
a child evokes from the environment. The latter is a possible example of the
evocative genotype-environment interactions noted on p. 70. What kinds of
responses do you think difficult children would elicit from their mothers?
Genetic influences on temperament increase during early childhood--an example of
the general principle noted above (see also Table 2-4, p. 72).
Goodness of fit: The degree to which a child's temperament is matched by her environment. The more effectively parents accept and adapt to the child's unique temperament, the better the fit. What might be a good fit for a child with a difficult temperament? For a child with a fearful temperament?
Finally, genetic differences influence a wide variety of traits related to temperament and personality: emotionality, activity level, sociability, fears and anxieties, attention span and persistence, morality and respect for authority.