1. The Human Heritage: Genes and the Environment
The Development of Children (5th ed.)
Cole, Cole & Lightfoot
Chapter 2

2. A World of Possibilities…
“If we go to all the trouble it takes to mix our genes with those of somebody else, it is in order to make sure that our child will be different from ourselves and from all our other children.”
—François Jacob, The Possible and the Actual

3. Overview of the Journey
Sexual Reproduction and Genetic Transmission
Genotype and Phenotype
Mutations and Genetic Abnormalities
Biology and Culture

4. Sexual Reproduction and Genetic Transmission
Mitosis: A Process of Cell Replication
Meiosis: A Source of Genetic Variation
Sexual Determination: Another Source of Variation

5. Genetic Code Chromosome: A threadlike structure made up of genes
46 in all human cells, except sperm and ova which have 23
Deoxyribonucleic acid (DNA): A long double-stranded molecule that makes up chromosomes
Genes: The segments on a DNA molecule that act as hereditary blueprints for the organism’s development
Model of DNA

6. DNA Replication
A strand of DNA replicates by splitting down the middle of the rungs of its ladderlike structure
Each free base picks up a new complementary partner:
Cytosine (C) pairs with guanine (G)
Adenine (A) pairs with thymine (T)

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

8. Genetic Variation Meiosis
The twice-over process of germ cell (i.e., sperm and ova) division that results in a zygote (with 46 chromosomes) at conception
Variation enhanced by “crossing over” during first phase...

9. The Process of Crossing Over

10. The Case of Twins
Monozygotic twins: Come from a single fertilized egg and have exactly the same genes (i.e., identical genotypes)
Sometimes called “identical twins”, but may not actually look identical due to the fact that phenotype interacts with the environment
Dizygotic twins: Come from two ova that have been fertilized at the same time, and consequently are no more alike than any two siblings

11. 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)

12. Sexual Determination
Human X and Y chromo-somes

13. Sexual Determination
Since a female is always XX, each of her eggs contains an X chromosome
In contrast, half of a man’s sperm 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

14. Genotype and Phenotype
The Laws of Genetic Inheritance
Genes, the Person, and the Environment
The Study of Genetic Influences on Human Behavior

15. Genotype + Environment  Phenotype
An Interaction
Genotype + Environment  Phenotype
Genotype: An individual’s genetic endowment
Environment: The totality of conditions and circumstances that surround an individual
Phenotype: The observable characteristics of an individual
Physical and psychological traits, health, behavior

16. Laws of Genetic Inheritance
Gregor Mendel ( ): Garden peas
Allele: The specific form of a gene coded for a particular trait
Homozygous: Having inherited two genes of the same allelic form for a trait
Heterozygous: Having inherited two genes of different allelic forms for a trait

17. Heterozygous Possibilities
Dominant gene: The allele that is expressed when an individual possesses two different alleles for the same trait
Recessive genes: The allele that is not expressed when an individual possesses two different alleles for the same trait
Codominance: An outcome in which a trait that is determined by two alleles is different from the trait produced by either of the contributing alleles alone

18. The Case of Blood Type

19. Sex-Linked Traits
Given that the X chromosome is much larger than the Y chromosome, most inherited sex-linked characteristics are carried on the X chromosome
Males are more susceptible to genetic defects than are females
If a daughter has a harmful recessive gene on one X chromosome, she will usually have a normal dominant gene on the other X chromosome to override it
A son who inherits a harmful recessive gene on his X chromosome has no such complementary allele to override the recessive gene’s harmful effects
Examples: Red-green color blindness, hemophilia, muscular dystrophy

20. Principles of Gene-Environment Interactions
Gene-environment interaction is a two-way process.
Interactions between organisms and their environments need to be studied in a broad, ecological framework because variations in the environment can have profound effects on the development of the phenotype.
Genetic factors often play a role in determining what environments individuals inhabit and how individuals shape and select their own experiences.

21. 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.

22. Canalization
The process that makes some traits relatively invulnerable to environmental events

23. Genes and Behavior
Only in cases where it has been possible to identify a specific gene that controls a specific pattern of phenotypes across all known environments where humans live has it been possible to make clear causal inferences from genes to behavior.
As a substitute in the vast majority of cases where multiple, unknown, genes are likely to be involved, behavioral geneticists rely on the study of various kinship relations to estimate the relative influences of the genotype and the environment on the phenotype.

24. Types of Kinship Methods
Family studies: Relatives who live together in a household are compared
Twin studies: Monozygotic and dizygotic twins are compared
Adoption studies: Children living apart from their biological parents are studied

25. 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

26. Mutations and Genetic Abnormalities
Down Syndrome
Phenylketonuria
Sickle-Cell Anemia
Klinefelter Syndrome

27. Causes of Genetic Abnormalities

28. Down Syndrome: A Chromosomal Error
Cause: More than 95% of children born with Down syndrome have 3 (vs. 2) copies of chromosome 21
Traits: Mentally/physically retarded; distinctive physical characteristics (e.g., slanting eyes, rather flat facial profile, ears lower than normal, short neck, protruding tongue, dental irregularities, small curved fingers, wide-spaced toes); more likely to die young
Incidence: 1:1000 births (increases with mother’s age: 1:100 by age 40, 1:32 by age 45, 1:12 by age 49)
Outlook: Supportive intervention that includes special education by concerned adults can markedly improve the intellectual functioning of some of these children

29. Phenylketonuria (PKU): A Treatable Genetic Disease
Cause: Defective recessive gene that reduces the body’s ability to convert one amino acid (phenylalanine) into another (tyrosine), resulting in retarded development of prefrontal cortex
Traits: Severe retardation
Incidence: 1:10,000 (more prevalent among whites than blanks; 1:100 people of European descent is a carrier of the recessive mutant gene)
Outlook: Feeding PKU infants a diet low in phenylalanine (e.g., avoiding milk, eggs, bread, fish), reduces the severity of mental retardation, although this does not eradicate its effects entirely

30. Sickle-Cell Anemia: Gene–Environment Interaction
Cause: Recessive gene (victims are homozygous, but heterozygous subjects are also mildly affected)
Traits: Abnormal blood cells cause circulatory problems (e.g., heart enlargement) and severe anemia
Incidence: 8-9% of U.S. blacks
Outlook: Crippling, but treatable with medication

31. Klinefelter Syndrome: A Sex- Linked Abnormality
Cause: Extra X chromosome (i.e., XXY)
Traits: Males fail to develop secondary sex characteristics (e.g., facial hair, voice change), are sterile, and most have speech and language problems
Incidence: 1:900 males
Outlook: May be treatable with testosterone replacement therapy

32. Survival Strategies Coevolution
Biology and Culture
Survival Strategies
Coevolution

33. Survival Strategies: Culture
Cultural artifacts, such as tools and clothing, greatly extend the range of environments in which human beings can reproduce and thrive
Cultural knowledge, such as the creation of “hazard prevention strategies,” serves to protect and support children to enable them to mature and reproduce

34. Coevolution of Tool-Making Abilities