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Today’s Topics
- Mechanisms of Heredity
- Biology of Heredity
- Genetic Disorders
- Research Methods in Behavioral Genetics
- Gene x Environment Interactions 1
The Process of Genetic Transmission
2 Chromosome: threadlike structure that contains the genetic information DNA: the genetic substance in chromosomes Genes: segments of DNA The Process of Genetic Transmission
- Genes
- Carry codes for production of proteins - Vital for cell functions
- Duplicate themselves (^) to Behavior
Cracking the Genetic Code
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The Process of Genetic Transmission
5 Chromosomes, Cells, and Sex: Terminology Autosomes the 22 pairs of chromosomes that are not sex chromosomes Sex chromosomes 23rd pair of chromosomes determines sex XX = female, XY = male Gametes sex cells: sperm and ova Zygote sperm and ovum united
The Process of Genetic Transmission
Gametes:
- Ovum
- Largest human cell
- The female germ cell (egg)
- 23 chromosomes (not pairs)
- 23 rd^ is always an X
- Sperm
- Smallest human cell
- The male germ cell
- 23 chromosomes (not pairs)
- 23 rd^ is either an X or a Y 7 Unite to form a single cell, the Zygote, which has 23 pairs of chromosomes Mother’s Genes Father’s Genes ½ of each pair ½ of each pair 8
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Complex Heredity
Complex Heredity
- Polygenic inheritance: Multiple genes 1 trait
- Complex behavioral dispositions
- Combination of several genes that ‘work’ together
- Environment plays a major role in gene expression
Genetic Disorders
- Inherited disorders
- Sickle-cell disease
- Huntington’s disease
- Abnormal number of chromosomes
- X-linked Inheritance 15
Inherited Disorders
- Sickle-cell disease
- Problem is inherited on a recessive allele
- Two recessive alleles = sickle cell disease
- Incomplete dominance of normal “dominant” allele = sickle cell trait
- Huntington’s disease
- Problem is inherited on a dominant allele
- Symptoms happen late in life, after most patients have reproduced & passed the trait on to a new generation. 16
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Abnormal Number of Chromosomes
- Down Syndrome (Trisomy 21) 17 Phenotype^ Genotype
X-linked Inheritance
- What happens if the gene is on a sex chromosome? - Females: If there’s a “bad” recessive gene on one X, there’s probably a dominant gene on the other X to suppress it - Males have only 1 X - e.g., hemophilia 18
X-Linked Inheritance Today’s Topics
Mechanisms of Heredity Biology of Heredity Genetic Disorders
- Research Methods in Behavioral Genetics
- Gene x Environment Interactions 20
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Heritability
nonshared environment shared environment heritability IQ adult IQ child Reading disability Personality Schizophrenia Major Depression Autism Hyperactivity
- Monozygotic (MZ) vs. Dizygotic (DZ) Twins “Identical” “Fraternal” Share 100% genes Share ~50% genes Twin Studies 27
Twin Studies
- The logic behind twin studies: If identical twins (same genes) resemble each other more than fraternal twins (different genes) do trait is influenced more by genes If identical twins (same genes) resemble each other the same as fraternal twins (different genes) do trait is influenced more by the environment (^28)
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Twins reared together vs.
apart
This keeps genes constant & changes the environment. Separated Identical Twins 30 A number of studies compared identical twins reared separately from birth, or shortly thereafter, and found numerous similarities. Personality, intelligence, abilities, attitudes, interests, fears, brain waves, heart rates, blood pressure 31 Biological Versus Adoptive Relatives
- Logic behind adoption studies resemblance to biological parents due to genes resemblance to adoptive parents due to environment Biological Versus Adoptive Relatives 32 Adoption studies suggest that adoptees (who are biologically unrelated to their families) tend to be different from their adoptive parents and siblings more similar to biological parents on a number of characteristics (e.g., personality & intelligence)
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37
- Range of reaction (graph)
- What’s not explained by heritability/genes is usually attributed to the environment
Influences of Genes vs. the
Environment
- Range of reaction 38 Influences of Genes vs. the Environment
Gene X Environment Interactions
39 Genes can influence traits which affect responses, and environment can affect gene activity.
Nature via Nurture
- genetic predispositions can
- influence how others respond to us.
- drive us to select and create particular environments.
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The Epigenetic Framework
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