Lecture 23 - Quantitative Genetics and Twin Studies

Describe the standard deviations from the mean

1. 66% of values lie within 1 standard deviations of the mean

2. 95% of values lie within 2 standard deviations of the mean

3. 99% of values lie within 3 standard deviations of the mean

How does inbreeding affect variability?

1. Reduces heterozygotes

2. Increases homozygotes

Broad sense heritability

Proportion of total variance that is due to genetic differences among individuals

Narrow sense heritability

Additive alleles raise or lower the value of a trait in an additive way

Artificial selection

A practice of breeding specific plants or animals together for the most desirable outcome

Hybrid vigor

Crossing two true breeding strains that result in larger size in the F1 generation (commercialized by the agricultural industry)

What causes the loss of hybrid vigor?

Independent assortment of F2 generation

What is the purpose of twin studies?

Used to tease apart role of shared genes and the environment

Monozygotic twins

Same fertilized egg (relatedness = 1)

Dizygotic twins

Different eggs fertilized by different sperm (relatedness = 0.5)

Concordance values

Percentage of pairs where both twins express the same trait among the alternative of one having it and one not having it

What is the correlation between concordance value and genetic components?

A higher value of this in MZ twins than DZ twins implies that trait has an important genetic component

Adopted individual studies

Shared environment BUT no shared genes. Provides a control and shows the effect of the environment alone

Describe IQ tests and twin studies

Suggested that IQ measure is largely genetic because in studies of MZT and MZA twins vs. DZT and DZA twins, the concordance value is higher in MZ

Schizophrenia

Loss of ability to organize thoughts and perceptions. Withdrawal from reality

Why does schizophrenia persist in the population?

1. Advantageous in the right combination with other genes

2. Tightly linked to advantageous genes

How do twin studies and personality relate?

Identical twins raised apart were as much alike as identicals raised together in terms of personality. Implies that environment plays little role