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BIOLOGY 202L Study Guide - Midterm Guide: Intron, Zygote, Adaptive Mutation

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School
Duke University
Department
Biology
Course
BIOLOGY 202L
Professor
John Willis

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Document Summary

Quantitative traits are influenced by genetics and by the environment. Phenotypic variance can be partitioned into genetic variance and environmental variance. Vp = va + vd + ve. Measures how much of the phenotypic variability is due to genetic variance and how much is due to environmental variance. Heritability h2 = vg/vp = r/s = vg/(vg + ve) Calculating the fraction of total phenotypic variance that is genetic. To calculate what proportion of the phenotypic variation is due to additive genetic effects. H2 is the proportion of variability that can be passed on from parent to offspring. Tells us whether selection on the parents will produce inherited changes in the offspring. The slope h2 allows us to predict how a population will respond to artificial or natural selection. Degree to which selection on the parents will produce inherited changes in the offspring is determined by the narrow sense heritability of the trait.

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Related Questions

Many traits are affected by theenvironment, but also have a genetic component. How can wepartition the sources of variation? Write a formula for this. Ifyou want to measure the sources of variation, how can this be doneexperimentally? Write out howyou can do this making specific reference to yourformula.

Heritability can be defined in two ways.What are these definitions and how are they different?

Not all genetic variation is the same. Whatis the difference between additive, dominance, and epistatic formsof genetic variation? Define all three, and update your formula. Inaddition, use a regression plot to schematize additive anddominance variation (ie, box 9.2).

Differential survival and reproduction canbe measured empirically, as can quantitative phenotypes of nearlyany organism. From these we can calculate selection differentialsand selection gradients. What are selection differentials andgradients?

Selection can act on quantitative traits ina variety of ways. Draw a diagram of what directional, stabilizing,and disruptive selection would look like on the distribution of atrait, then describe and explain the differences. Write concisedefinitions next to each type of selection.

If two populations differ in a trait thathas a high heritability, is it valid to conclude that the twopopulations differ genetically with respect to that trait? Useevidence from section 9.7 to explain why or why not.

1. Clover tongue is the ability to roll ones tongue into threedistinct lobes and is probably inherited as a dominant, simpleMendelian trait. In a population 90.25% of individuals can NOT rolltheir tongue into a clover tongue (i.e. they do not possess theclover tongue trait). What is the expected frequency ofheterozygous individuals in this population?

0.9500
0.9025
0.0950
0.0025

2. Assume that in the F2 of a series of crosses, 1/256 of theoffspring resemble one of the parents. How many gene loci areinvolved in producing these results?

8
6
4
3

3. Assume that three gene loci are involved in determiningphenotypes of F2 in an additive manner. How many phenotypic classesare expected?

9
8
7
6
4
2

4. The following values were estimated for corolla length in apopulation of honey-suckle. What is the narrow-sense heritabilityfor this trait in the population?

VE = 4.2

VA = 2.6

VD = 0.9

VI = 0.3

5. Toxin levels were measured in milkweed plants from a largecornfield in Iowa and found to have a mean level of 28.2 mg pergram and a variance of 15.3. Seeds were collected from these plantsand germinated in a single, large greenhouse allowing all plants togerminate and grow under identical environmental conditions. Atmaturity, toxin levels were assessed across all of these plants.The mean toxin level was 33.2 mg per gram with a variance of 8.70.What is the estimated broad-sense heritability for this trait inthis cornfield population of milkweed? Remember that H2= broad-sense heritability = VG/VP.