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PCB 4674 Lecture Notes - Lecture 53: Heritability, Stabilizing Selection, Directional Selection

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tanwasp406
14 Apr 2018
School
FAU
Department
Process Cell Biology
Course
PCB 4674
Professor
Theisen Timothy C.

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Document Summary

Proportion of phenotypic variance explained by additive genetic variation. This is what causes offspring to resemble parents and causes populations to evolve predticably in response to selection. Mid parent versus mid-offspring provides an estimate of narrow-sense heritability. Difference in fitness associated with certain trait values. This is the degree of which the breeding population differs from the general population (in terms of trait value) Weak selection = mean pop and reproducing individuals is similar. Strong selection = mean of reproducing individuals is very different in general population. S = selection h^2 = narrow sense heritability. It is the amount of change one could expect in trait value for some offspring which is proportional to the strength of selection, but not all traits respond strongly. If the heritability of a character is zero, how would it act in a population with strong selection against this character. The mean goes unchanged, but there are less of the extremes.

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Related Questions

Hey guys! I'm a little stuck with this question, with calculating the total genetic variance I'm not sure whether my answers are correct.

(VG = VA + VD = VI

(Broad sense heritability) H2 = VG/VP

(Narrow Sense heritability) h2 = VA/VP

(Response to Selection) R = h2 x s

A plant breeder has determined the following variances for yield of corn:

Total phenotypic variance 100

Additive genetic variance 30

Dominance genetic variance 50

Environmental variance 20

Assume that there is no genetic-environmental interaction or other variances. a) Calculate the total genetic variance.

b) Calculate the broad-sense heritability indicated by these results.

c) Calculate the narrow-sense heritability indicated by these results.

d) The breeder wishes to improve yield. The average yield in the starting population is 400. Plants with an average yield of 500 are selected for breeding. What is the expected average yield among the offspring of the selected plants?

12. Imagine a population of captive giant tortoises housed at the Charles Darwin Research Station. The captive breeders are attempting to increase body-size and select for saddle-shaped shells in response to ecotourism demands for giant tortoise rides. A parental population of giant tortoises had an average body mass of 250 kg. The captive breeders selected 10 males and 10 females from the general population that had an average body mass of 275 kg. Following this round of mating, the surviving offspring were an average of 260 kg when full grown.

a. Calculate the narrow sense heritability (h2) for body size in this population of giant tortoises

b. If the breeders select 20 of the smallest adult individuals from the general population that have an average body mass of 200 kg, what will be the expected average body mass of their offspring? Assume that the narrow sense heritability stays the same.

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.