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Twin Studies

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Andria Tan

on 6 February 2014

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Transcript of Twin Studies

Twin Studies
Presenters: Jessica, Jill, James, Paolo, Rachael & Andria
Content
What are Twin Studies?
Uses of Twin Studies
Limitations of twin studies
The Nature VS Nurture Debate
Twins Databases
The Classical Twin Study Design (Assumptions)
Conclusion
Types of Twin Studies

The Nature VS Nurture Debate
Uses of Twin Studies
Nature
- Refers to genetic or hormones behavior

Nurture
- Refers to environment and experience

Video: Identical Strangers
- Paula and Elyse separated and adopted at birth.

- Met for the first time after 35 years

- Will they have the same needs, desires, and
ambitions?


The Classical Twin Study design (Assumptions)
1. Equal Environments
Both Identical & Fraternal twins are raised in the same homes there experience equal environments.
2. Random Mating
-Researchers assume that people are more likely to choose partners that are different from themselves.

-IF NOT, if mates are similar to themselves, fraternal twins could then share more than 50% of their genes.
3. Gene - environment interaction
Assume 1 out of 2 types of interactions

EITHER : Both the environment & the gene itself separately influence a particular trait.

OR: Interactions btw. the gene & the environment that influences traits.
4. Genetic Mechanisms
- Dominant/Recessive

-Addictive ( Genes mix together )

Twin studies in general assume 1 type of mechanism is operating for a particular trait.
Limitations of Twin Studies

twin studies useful for molecular-genetic studies (study of the structure and function of genes at a molecular level)
Twins Databases
comparison allows the study of the effect of genotype x nature on traits
Conclusion
Q & A
Dizygotic Twin Studies
are useful for linkage studies
Genetic Linkage: tendency of genes proximal to each other on a chromosome.
Therefore linkage studies are useful for mapping genes
Monozygotic Twin Studies
have shown that disease outcome can be different for 2 individuals with identical make-up
Monozygotic twin concordance also gives important information about disease penetrance.
example:one of a pair of monozygotic twins with a cleft lip and palate
Penetrance: proportion of affected indviduals among the carriers of a particular genotype
Nature vs Nurture Debate
Progression in genetics
Ascertainment Bias
Environmental Noise
Difficulty in Phenotypic study
Modern reliance on animal research
Cannot explain complexity
Interspecies difference
Longitudinal Data of Large Samples
Not only the twins but as well as their families
Classical
The studying of twins raised in identical family environments
Monozygotic twins share all of their genes
Dizygotic twins share only about 50% of genes
Compares similarity between sets of monozygotic twins and similarity between dizygotic twins
A specific trait
Excess resemblance likeness are due to the genes rather than the environment
Advantage


Researchers use this method and modify it to estimate the heritability of traits
Disadvantages
Requires longitudinal study to be conducted
Cannot take into account twins of different sexes
Biased results
Structural Equation Modeling
The examination of the effect of latent variables and observable variables on the possible phenotypic differences between individuals
Gender differences are involved in this twin design
Advantage
Disadvantage
Requires longitudinal study to be conducted
Extended Twin Designs
Includes not only subject of study, in this case, the twins, but as well as parents, siblings, spouses and offspring of the subject
Advantages
Able to pinpoint effects of age differences in heritability
Shortcut for longitudinal study
Provides platform to evaluate social interactions within and between generations, cultural learning and non-random mating
Case Control Studies
Utilizing identical twins in an ideal case-control study
Determine nature of associations between traits of an individual, either casual or a product of inherited genes
Advantage
Disadvantages
- Ongoing for centuries

- Each individual is affected by genetic makeup and environment.

- No clear stand


- Maintaining Constant Contact with twins

- Genotypic Studies are costly & requires extensive labor

- Depth of qualitative study is compromised due to reliance on surveys & questionnaires

Nature vs Nurture
- Nature: innate behavior

- Nurture: learned behavior

- Twin and adoption studies: tells us to which extent family resemblance is

Helps to assess the effect of age differences on heritability and to assess differential gene expression as a function of age
Require longitudinal study to be conducted
May not be ethical
Full transcript