1. Genetic Foundations Heredity & Environment
Chapter 2: Genetics
Genetic Foundations
Heredity & Environment

2. Genetic Foundations Chromosomes: limits
“Each of us carries a “genetic code” that we inherited from our parents. Because a fertilized egg carries this human code, a fertilized human egg cannot grow into an egret, eagle, or elephant.”

3. Genetics and Behavior
Nucleus
Chromosome
Gene
Cell
DNA

4. Genes: Our Biological Blueprint
Human Genome Project
Initial phase completed about the year 2000
Humans have 20,000 – 25, 000 genes (21,667)
There are far more proteins than genes – million
Genes (DNA) are dependent- collaborate with other sources of information
Gene expression/activity is affected by context or environment
Context is affected by hormones, light, nutrition, etc.

5. The Sex Cells Sex cells are formed by meiosis rather than mitosis.
Gametes (sperm and ova) have only 23 chromosomes total.
At conception, these two unite resulting in a full complement of 46 chromosomes (23 pairs).
A fertilized egg is called a zygote.

6. Sources of Genetic Variation
Alleles are normal variations of a gene, found at the same location.
A child who inherits the same allele (type of gene) from both parents is homozygous for that trait.
A child who inherits different alleles from each parent is heterozygous for that trait.

7. Sources of Variation Genetic Expression Influenced by the environment
hormones
light
nutrition
behavior
stress (cortisol may cause a fivefold increase in DNA damage)

8. Sources of Genetic Variation
Patterns of Genetic Inheritance
Dominant-recessive: the dominant gene (allele) will determine the characteristic

9. Patterns of Genetic Inheritance Dominant-recessive inheritance
Examples of dominant genes
Dark hair, curly hair, dimples, types A & B blood (vs. type O), traits for normality in vision, hearing, pigmentation, etc.
Huntington’s Disease

10. Patterns of Genetic Inheritance Dominant-recessive inheritance
Examples of recessive genes:
Cystic fibrosis, PKU, Tay-sachs disease. Sickle-cell anemia

11. Patterns of Genetic Inheritance Co-dominance and Additive
Co-dominance: both alleles contribute to the phenotype, although not to the same degree.
Additive: They contribute about equally (50%-50%).
Example of Co-dominance;
Sickle-cell anemia

12. X-linked (sex-linked) inheritance
Female children receive an X chromosome from the father which matches locations on the mother’s X.
Male children receive a Y from the father, which does not have all the gene locations of an X.
The defective gene on the mother’s X is offset by the gene on the normal X in females, but not in males.
So, males will show evidence of the defective gene (e.g., hemophilia, RG colorblindness).
Females will be normal, but carriers of the defective gene.

13. Polygenic Inheritance
Many genes interact to influence the characteristic
Most psychological characteristics are polygenic
(Where environmental factors are included, traits are said to be multi-factorial.)

14. Chromosomal Abnormalities
Usually happen during meiosis
Involve breakage and failure to separate
Usually result in miscarriage
Those most commonly survived are:
Down syndrome (trisomy 21)
Sex-linked abnormalities

15. Sex Chromosome Abnormalities
XXY (Klinefelter) may have verbal difficulties. Tall, underdeveloped testes, possible breasts. 1/800 live male births.
XO (Turner) have trouble with math and spatial skills. Short and have webbed neck; may be infertile. 1/2500 live female births
XYY (Are they more aggressive, antisocial?)

16. Gene-linked Abnormalities
Over 7000 known (most rare), including:
Cystic fibrosis
Diabetes
Hemophilia
Huntington
PKU (phenylketonuria)
Sickle-cell anemia
Spina bifida
Tay-sachs disease

17. Genetic Counseling – for whom?
Family history of disease, mental retardation, physical defects
History of miscarriages
Mother over age 35 (rate of abnormality begins to rise sharply)

18. Prenatal Diagnostic Methods
May cause miscarriage (except ultrasound, maternal blood samples)
Is the problem correctible?
Genetic engineering is still in the future.
Often the only decision is whether or not to abort the fetus.

19. Prenatal Diagnostic Methods
Chorionic villi sampling (6-8 weeks);
detects genetic defects; risk of miscarriage, limb deformity
Amniocentesis – (11 weeks, best after 15 weeks); detects genetic defects; smaller risk of miscarriage

20. Infertility 1 in 6 couples in U.S. Fertility technology (IVF, donors)
Waiting too late
Sexually transmitted diseases
Fertility technology (IVF, donors)
Adoption
Babies culturally unavailable

21. Environmental Influence

22. Environmental Influence
Impoverished environment
Enriched environment
Rats reared in an environment enriched with playthings show increased development of the cerebral cortex

23. Twins Identical Twins Fraternal Twins
develop from a single fertilized egg that splits in two, creating two genetically identical organisms
Fraternal Twins
develop from separate eggs
genetically no closer than brothers and sisters, but they share a fetal environment
Identical
twins
Fraternal
Same
sex only
Same or
opposite sex

24. Multiple Births – fraternal twins
Dizygotic (two zygotes)
Share approximately 50% of their genetic heritage like any two siblings.
Major causes are maternal age and fertility drugs.
Twinning dramatically on the increase since the 1970s.

25. Multiple Births – identical twins
Monozygotic – one zygote (same fertilized egg)
Share 100% of genetic heritage
Occurs about 3 per 1000 live births worldwide
Factors may include temperature and oxygen levels and late fertilization

26. Genetics Research Behavior Genetics
study of the power and limits of genetic and environmental influences on behavior
Molecular Genetics
subfield of biology that studies the molecular structure and function of genes

27. Nature-nurture Research
Molecular genetics
Human Genome Project
Behavioral genetics
Twin studies
Equal environment assumptions
Adoption studies
Concordance rates

28. Epigenesis – ongoing nature/nurture exchanges (bi-directional)
Reaction range
Canalization
Genetic-environmental correlation
Passive
Evocative
Active (niche-picking)