Lecture 4 Flashcards
Polygenetic trait
Trait that is caused my multiple genes.
Why are there fewer phenotypes than genotypes?
Some genotypes result as the same phenotypes.
Additive genes
Independent effects of alleles that add up.
- Skin color as an example (multiple genes contribute to the final skin color)
Simple traits (Mendelian traits)
1- One or few genes
2-Big effects from each gene
3-Causation is determenistic
4-We know the biological mechanisms
5-Environment and experiences don’t do much
Example: Huntington’s disease, hemophilia, cystic fibrosis
Complex traits
1-Influenced by many genes
2-Tiny effect from each gene
3-Causation is probabilistic
4-We have little idea of mechanisms
5-Environment plays a big role and interacts with genes.
Examples: Alzheimer’s disease, schizophrenia,depression
What is Nurture
Environmental effect
What is Nature
Effects of genes
What are family-based methods
1-Adoption study: experiment of nurture
Twin study
Experiment of nature
What is the first adoption study?
1- 47 adopted kids with a biological mother with schizophrenia.
-More than 10% had schizophrenia.
2- 47 adopted controls (mothers without schizophrenia)
- Zero was diagnosed with schizophrenia.
Result: Schizophrenia is herited through genetics.
Recent adoption study
The same trait was tested with a bigger data set and also showed that schizophrenia is inherited genetically
What are possible issues with adoption studies?
1-Not representative (rich adopts poor)
2-Prenatal environment
3-Selective placement ( Adoption center checks the match between parent and child and gives the adoption according to it.
Monozygotic twins
Single egg fertilized by single sperm then splits in two
Dizygotic twins
Separate eggs fertilized by separate sperm.
Heritability
Proportion of phenotypic variance that can be accounted for by genetic differences among individuals.
Shared enviroment
All nongenetic influences make family members similar to one another.
Unique environmental effects
Non-genetic influences that are independent (uncorrelated) for family members include error of measurement.
Issues in twin studies
Equal environment assumption: Even though monozoygotic twins share more similar environment than dizygotic twins it is assumed that they are equal if not the genetic influence estimates would inflate.
Are sample twins representative of the population?
Yes! twins are similar to non-twins for most phenotypes. Twins are only unrepresentative regarding the first few years of life.
