Lab practical 6 Flashcards
What are complex traits and how are they expressed?
Traits that are expressed by more than one gene. Tend to be quantitative.
What is the difference between continuous and discontinuous (discrete) variables?
Continuous: traits that can be expressed in many ways, not just one or the other.
Discontinuous: traits that are either + or -.
What is the formula and concept of the mean?
Formula: x-bar= summation of observed values/N
Concept: in a frequency distribution, the mean is the peak of the bell curve.
What is the formula and concept of variance?
Formula: V= summation of(xi - x-bar)^2/N-1
Concept: variance tells us how spread out data is within frequency distribution
What is standard deviation?
The square root of variance, helpful for characterizing variation when looking at the curve.
Describe this equation: Vp = Vg + Ve
This equation tells how much a trait is related to genetics vs. the environment.
Vp: total phenotypic variance
Vg: relative amount of variance due to genetic variation
Ve: relative amount of variance due to environmental factors
What is heretability?
Amount of phenotypic variance attributed to genetic variation.
What is the difference between broad sense heritability and narrow sense heritability?
Broad sense heritability takes into account different types of genetic variation, narrow sense heritability only measures the additive genetic effects since there are hidden aspects to the other genetic components.
Broad sense: H^2 = Vg/Vp
Narrow sense: h^2 = Va/Vp
What three different generic categories to geneticists usually subdivide Vg into?
Va: the variance due to additive genes that contribute to the trait
Vd: the variance due dominant vs recessive alleles
Vi: the variance due to epistasis (when one gene affects another)
How can you measure heritability using covariance and the correlation coefficient (r)?
- Use covariance formula to find covariance: cov(X,Y)= summation of (xi-xbar)(yi-ybar)/N
- X is independent variable, Y is dependent variable
- Find correlation coefficient (r observed) by dividing covariance by standard deviation
- h^2= r/r(expected which is 0.5)
How do you estimate heritability using linear regression analysis?
- Plot the independent variables on the x axis and dependent variables on y axis of graph.
- The slope of the best fit trend line estimates h^2.
What does the correlation coefficient (R^2) in a linear regression analysis estimate?
The predictability (goodness of fit) of the linear equation to observed data in reality
How is R^2 affected by slope and error?
An increase in slope will positively affect R^2 and an increase in error will negatively affect R^2. Error is increased when the value of R^2 increased and slope remains the same.
How can one estimate heritability by comparing a heterogenous population to a homogenous population?
You can use a homogenous population such as clones and identical twins/strains because Vg for them is always 0, making Vp=Ve. Then you can solve for Vg
What are some of the different ways to predict heritability?
- Comparing a heterogenous population to a homogenous population such as clones or identical twins.
- Use covariance and correlation coefficient (r) to calculate h^2.
- Use linear regression analysis to estimate h^2. (Slope)
