1. Heredity and Environment: The Origins of Individual Differences
PSYC 206: Life-Span Development
Lecture 2
Aylin Küntay

2. Show and Tell (from Merve Özgür)
TV and children

3. Overview
will discuss the genetic and environmental basis of development and individuality
each of us is the product of a unique set of genes and a unique pattern of experiences
The frightening part about heredity and environment is that parents provide both.

4. Genetic transmission
there are two kinds of cells in the body
somatic cells: all the cells in the body except the reproductive cells
germ cells: reproductive cells
somatic cells govern the body’s formation of bones, muscles, and organs
each of these contains chromosomes, the threadlike structures that convey heredity
all members of a species have the same number and type of chromosomes
every somatic cell has the same 23 pairs of chromosomes in human body

5. Chromosomes and genes
the members of each pair are arranged together, although each may contain different kinds of info
each chromosome, in turn, is made up of genes, the smallest unit of heredity
estimate that about 44,000 genes are strung like beads on each chromosome pair-- around 1 million genes across the 23 pairs
each gene is different from the other, and each has a “message” to contribute to the individual’s total genetic code

6. Chromosomes, genes, and DNA
two kinds of messages
one kind that makes an individual distinctively human-- hands rather than paws; lungs rather than gills
the other makes a human a unique individual as compared to other humans
genes and chromosomes are composed largely of a complex chemical called DNA

7. during cell division, each gene makes a copy of itself
Mitosis
during development, somatic cells divide and reproduce in a process called mitosis
ensures cell reproduction and growth
during cell division, each gene makes a copy of itself
causing each cell in an individual’s body to have the genetic content as every other cell
the 46 chromosomes in each cell grow and then split lengthwise to double their number
each identical set moves toward opposite poles of the cell
the cell then reorganizes itself into 2 equal daughter cells-- the exact replicas of original

8. Cell Replication Mitosis
The process of somatic (body) cell duplication and division that generates all the individual’s cells except sperm and ova

9. Meiosis
germ cells (sperms and ova) are the reproductive cells of the body
they contain only 23 chromosomes
when a sperm and ovum combine, the resulting organism has the correct number of 46 chromosomes
germ cells are produced in a halving process called meiosis
during meiosis, the chromosome pairs separate twice to form four daughter cells, each containing 23 chromosomes

10. Meiosis
each sperm or ovum produced in meiosis contains only half of each parent’s pool of about a 1 million genes
a process called crossover ensures that genes from each parent are not always transmitted in blocks
before the first division of meiosis, parts of each paired chromosome may break off, and the parts may attach themselves to the other chromosome in the pair rather than to the chromosome from which they broke away

11. The Process of Crossing Over

12. Principles of gene transmission
the separation of chromosome pairs during meiosis
also the thousand of genes in each chromosome can be reshuffled to different chromosomes by crossover
the combination of these chromosomes into a new set of 23 pairs during fertilization
of the 23 pairs of chromosomes in human cells, 22 shape the individual’s general mental and physical characteristics
the chromosomes of the 23rd pair determine the sex of the organism
XX or XY?

13. Sexual Determination
In 22 of the 23 pairs of chromosomes found human somatic cells, the two chromosomes are of the same size and shape, and carry corresponding genes
Chromosomes of pair 23 can differ, however, and this determines a person’s sex
Females: Both members of chromosome pair 23 are of the same type and are called X chromosomes (i.e., XX)
Males: In chromosome pair 23, one X chromo-some is paired with a different, much smaller chromosome called a Y chromosome (i.e., XY)

14. Sexual Determination
Human X and Y chromo-somes

15. Sexual Determination
Since a female is always XX, each of her eggs contains an X chromosome
In contrast, half of a man’s sperms carry an X chromosome and half carry a Y chromosome
If a sperm containing an X chromosome fertilizes the egg, the resulting child will be XX, a female
If the sperm contains a Y chromosome, the child will be XY, a male

16. Genetic basis of sex
in the 23rd pair of chromosomes, we have the sex chromosomes (X and Y) that identify whether an individual is male or female
the X and Y chromosomes also determine sex-linked inheritance
a number of hereditary defects in males are caused by recessive genes carried on the X chromosome, such as those causing color blindness, hemophilia
a male does not have another X to dominate the effects of a recessive gene, so it is expressed
in female offspring, the recessive characteristics on one of the X chromosomes would be masked

17. Genetic defects
genetic abnormalities that have implications for survival and later development may be inherited in several ways
recessive genes carried on the X chromosome (e.g., color blindness)
paired recessive genes on the other 22 pairs of chromosomes that do not affect sex (e.g., albinism)
gross chromosomal abnormalities-- the absence of a chromosome or a part of one, or the presence of an extra one (e.g., Down’s syndrome)

18. Genetic defects
could also be classified by their effects: 4 genetic anomalies
severe genetic anomalies with early death (e.g., Tay-Sachs disease)
chronic genetic anomalies with good life expectancies (e.g., Down’s syndrome)
treatable genetic anomalies with recurrent episode (e.g., hemophilia, sickle cell anemia)
remediable genetic anomalies with improvement of symptoms (e.g., PKU)

19. Tay-Sachs disease
a metabolic disorder that causes substances to accumulate in the brain, causing degeneration of the nervous system or the brain tissue: occurrence 1 in 300,000 births
among Ashkenazy Jews: incidence 1 out of 3,600
because of lack of an enzyme that breaks down fats in brain cells, leading to fat accumulation
caused by two recessive genes, so that parents who are both carriers have a 25% chance of having a child with Tay-Sachs
results in mental and motor deterioration, blindness, convulsions, and death by the time the child is 3 or 4

20. Down syndrome
a chromosomal disorder typically associated with an extra chromosome 21
effects include mental retardation and a distinctive appearance that include flattened faces
associated with defects of the heart, sometimes causing early death
the likelihood of occurrence increases dramatically with the age of the mother
fewer than 1/1,000 have Down syndrome, whereas the incidence is 74 times greater for women between the ages of 45 and 49

21. Sickle cell anemia
the red blood cells change their shape and block the flood of blood through small vessels, causing pain and tissue death if the condition is not treated properly
occurs most frequently in regions of Africa, where malaria is prevalent-- the trait is thought to be a protective reaction of the body against malaria parasites
10% of African Americans in the US are carriers of this trait

22. PKU (Phenylketonuria)
a problem involving the metabolism of protein-- occurs when the body fails to produce an enzyme that breaks down phenylalanine, an amino acid
abnormal amounts start accumulating in the blood after a few months and harm the developing brain cells, causing retardation
if the condition is diagnosed early, a restricted diet during childhood can prevent retardation

23. Studying gene-environment interactions
a certain genotype will interact with the environment to exhibit a phenotype-- the organism’s observable characteristics
e.g., Winchester’s experiment with Himalayan rabbits
Gottesman proposed a limit-setting model, where genes do not determine development precisely, but instead establish a reaction range within which development will occur

24. Range of Reaction
The effect of environment on the expression of a gene for fur color in the Himalayan rabbit.
Under normal conditions only the rabbit’s feet, tail, ears, and nose are black. If fur is removed from a patch on the rabbit’s back and an ice pack is placed there, creating a cold local environment, the new fur that grows in is black.

25. Canalization
the notion of canalization emphasizes the narrow variation of the phenotype despite wide variation in environmental conditions
as opposed to the notion of reaction range focusing on the wide variation in the phenotype
when development of a certain behavior is highly canalized, environmental events do not cause a big change in the developmental process
e.g., only the most severe cases of language deprivation seem to cause deviations from a normal course of language development

26. Studying genetic influences: Family resemblance
Heritability coefficient
the child receives a random selection of about half the parents’ genes
50% of genotype (the total set of genes that an individual inherits) shared with each parent and sibling
the family-study approach traces continuities of characteristics over generations of the same family
one famous example is Henry Goddard’s study of the Kallikak family (1912)

27. Studying genetic influences on behavior
it is unethical and impossible to study the reaction range of a trait under different experimentally manipulated environmental conditions
in order to study the heritability of a behavioral characteristic, behavioral geneticists rely on family studies
comparing family members to see how similar they are in one or more traits

28. the Kallikak family study
Kallikak had two lines of families, one by a retarded working class woman, the other by a woman of normal intelligence from an aristocrat family
Goddard traced 5 generations of Kallikak’s offspring from these two lines
of the 480 descendants of the working class woman, he identified many as alcoholic, criminal, or retarded
none the 496 descendants of the other woman had the above characteristics
he concluded that the differences could be attributed to the different genetic endowments of Kallikak’s two mates
anything wrong in Goddard’s reasoning?

29. Adoption studies
if Goddard had arranged for some of the Kallikak’s descendants from one family to be raised in the homes of the other family, he could have better separated the influence of the genes and environment
this is the logic of studying the development of adopted children
will a child turn out be more like the biological parent, with whom he/shares a considerable genetic constitution, or more like adoptive parent, with whom he/she shares an environment

30. Twin studies
monozygotic twins are genetically identical because they come from one fertilized egg (vs. dizygotic twins, who are like siblings)
since they share the same genetic constitution, any differences between the pairs of an MZ pair are thought to be caused by the environment
assuming that MZ twins share environments that are no more similar than those shared by DZ twins
Plomin-- a behavioral geneticist-- compared MZ and DZ twins with respect to such temperamental characteristics as level of activity and sociability
found 0.55 correlation between MZ twins; no correlation in DZ twins, indicating the role of inherited factors

31. Family and Adoption Results for Extroversion
Type of Relative
Correlation
% Shared Genes
MZ twins raised together
.51
100%
DZ twins raised together
.18
50%
MZ twins raised apart
.38
DZ twins raised apart
.05
Parents/child. living together
.16
Adoptive parents & children
.01 0%
Siblings raised together
.20
Siblings raised apart
-.07
Loehlin, 1992