Today’s Topics The Process of Genetic Transmission Development...Human Development: Genetic...
Transcript of Today’s Topics The Process of Genetic Transmission Development...Human Development: Genetic...
Human Development: Genetic Foundations
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Today’s Topics
• Mechanisms of Heredity
– Biology of Heredity
– Genetic Disorders
• Research Methods in Behavioral Genetics
• Gene x Environment Interactions
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The Process of Genetic Transmission
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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
• The Human Genome
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The Process of Genetic Transmission
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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)
– 23rd is always an X
• Sperm
– Smallest human cell
– The male germ cell
– 23 chromosomes (not pairs)
– 23rd 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
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Human Development: Genetic Foundations
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Review:
23 from Father
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23 from Mother
+ =
1 Zygote with 23 pairs
• Phenotype
– An organism’s
actual observable
characteristics
Genes and Behavior
• Genotype
– A particular set of
genes a person inherits
from his or her parents
Alleles
Two forms of the same gene
• Appear at the same place on both
chromosomes in a pair
• One inherited from each parent
• Homozygous – the two alleles are alike
• Heterozygous – the alleles differ
Dominant-Recessive
Inheritance
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Complex Heredity • Incomplete dominance
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
– Down Syndrome
• X-linked Inheritance
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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.
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Abnormal Number of Chromosomes
• Down Syndrome (Trisomy 21)
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Genotype Phenotype
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
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X-Linked Inheritance Today’s Topics
Mechanisms of Heredity
Biology of Heredity
Genetic Disorders
• Research Methods in Behavioral Genetics
• Gene x Environment Interactions
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Human Development: Genetic Foundations
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Research Methods in Behavioral Genetics
• What is Behavioral Genetics?
– Branch of genetics that deals with inheritance of behavioral and psychological traits (p. 49)
• Family Resemblance Studies
• Twin Studies
– Monozygotic Twins
– Dizygotic Twins
• Adopted vs. Biological Children 21
Heritability
• Proportion of a trait’s variation in a population due to genetic factors
Heritability
= a statistical estimate of how much of the variability in
people‘s physical characteristics is explained by their genetic
makeup
Family Resemblance Studies
3 Factors:
• Genes
• Shared Environment
• Non-shared Environment
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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
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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
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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
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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
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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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Sibling Studies
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However, even biologically related children turn out to be very different from one another, even when raised in the same family.
So investigators ask:
Do siblings have different experiences within the same family? (nurture)
Even though biological siblings have 50% of the same genes, what effect does the other 50% of non-shared genes have? (nature)
Shared & Nonshared Environments
Ultimate question: What is the effect of parenting?? (nurture)
Parenting does have an effect on both biologically related and unrelated children.
Influences of the Environment
Parenting has greatest influence on children’s
Attitudes, Values
Manners, Beliefs
Faith, Politics
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Small Group Discussion: Which trait is most influenced by heritability?
Shared environment? Non-shared environment?
Twin & Adoption Studies Problems
• Shared environment overestimated
• Same genes, different expression
• Complex genetic interactions ignored
• Based on faulty assumptions
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–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
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Influences of Genes vs. the Environment
Gene X Environment Interactions
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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.