Quantitative Genetics

Question 1

Family Design

Answer 1

Is a study design that focuses on biologically related individuals and whether/not they have similarities in their environmental influence.
- with complex traits, the more closely related individuals are to each other the more likely they are to share risk alleles and the higher the chances are to develop the trait.
-when considering beliefs and attitudes, environmental contributions are more similar in individuals raised together, although behaviour “runs in the family”, the family resemblance can be due to nature/nurture.
-In the study design, parents are “genetic and environmental” they both share heredity and environment with the offspring.

Question 2

Adoption Design

Answer 2

Is a study design whereby adoption creates pairs of genetically related individuals who don’t share a common family environment and also produces family members who share a family environment but are not genetically related.
-In this study design there are “genetic” parents, who are biologically related to the child given up for adoption, and “environmental” parents, who are the adoptive parents who took in the genetically unrelated child.
-“Genetic” and “Environmental” siblings can also be studied
-Genetic factors appear to be important for most psychological traits that have been assessed in adoptive studies, for example, children with schizophrenic parents have a higher risk of developing the disorder, regardless of whether they are raised by “genetic” or “environmental” parents
-Family resemblance is not based solely on the family environment, it’s not true for all traits, ex, alcoholism needs environmental stimulus to develop, this is gene-environment interaction

Question 3

Twin Design

Answer 3

-Monozygotic twins (MZ): are identical twins who developed from one zygote.
- they are commonly used to study genetic factors of a trait due to their genes being so similar, compared to first-degree relatives, who are 50% genetically similar.
-Dizygotic twins: are twins that developed from separated fertilized eggs. making them first-degree relatives, who are 50% genetically similar.
-Greater similarity found between dizygotic twins could be due to environmental influence and monozygotic twins would be due to genetic influence.

When performing a twin study design, twins of the same gender are to be used to eliminate any variations that could skew the study

The equal environment assumption of the twins’ methods, assumes the environment is the same for both types of twins raised in the same family.
- if the assumption is violated, it’s because identical twins experience more similar environments than fraternal twins, the assumption would inflate the estimates of the genetic influence
- This is tested by the weight of identical twins prenatally differs more from that of fraternal twins due to the prenatal competition and identical twins treated as a pair will continue to look alike than fraternal twins treated as individuals, who will show differences. The differences between the types of twins are due to their experiences not violating the equal environments assumption because the differences are not environmentally influenced.

Identical twin Con:
-Twins are not the true representation of the general population because they are born premature and their intrauterine environment can be challenging since they shared such a small space, which will affect their weight, which is 30% lighter than an average child.
-Twins are more likely to develop language, mostly verbal ability, much slower.