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Chapter 23: Problem 15

If one is attempting to determine the influence of genes or the environment on phenotypic variation, inbred strains with individuals of a relatively homogeneous or constant genetic background are often used. Variation observed between different inbred strains reared in a constant or homogeneous environment would likely be caused by genetic factors. What would be the source of variation observed among members of the same inbred strain reared under varying environmental conditions?

Short Answer

Expert verified
Answer: The primary source of variation in the phenotype is the influence of the environment on phenotypic development.

Step by step solution

01

Understand the inbred strain condition

Since the inbred strains have a relatively constant genetic background, the genetic differences between the individuals will be minimal.
02

Consider the influence of varying environments

When members of the same inbred strain are reared under varying environmental conditions, these conditions might lead to differences in their phenotypic traits.
03

Identify the source of variation

As there is minimal genetic variation within the same inbred strain, the source of variation observed among members of the same inbred strain reared under varying environmental conditions is likely due to the influence of the environment on their phenotypic development.
04

Conclusion

The source of variation observed among members of the same inbred strain reared under varying environmental conditions is the influence of the environment on phenotypic variation.

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Most popular questions from this chapter

In a series of crosses between two true-breeding strains of peaches, the \(F_{1}\) generation was uniform, producing 30 -g peaches. The \(\mathrm{F}_{2}\) fruit mass ranges from 38 to \(22 \mathrm{g}\) at intervals of \(2 \mathrm{g}\) (a) Using these data, determine the number of polygenic loci involved in the inheritance of peach mass. (b) Using gene symbols of your choice, give the genotypes of the parents and the \(\mathrm{F}_{1}\).

Define the term broad-sense heritability \(\left(H^{2}\right) .\) What is implied by a relatively high value of \(H^{2}\) ? Express aspects of broad-sense heritability in equation form.

Corn plants from a test plot are measured, and the distribution of heights at \(10-\mathrm{cm}\) intervals is recorded in the following table: $$\begin{array}{cc}\text { Height }(\mathrm{cm}) & \text { Plants (no.) } \\\100 & 20 \\\110 & 60 \\\120 & 90 \\\130 & 130 \\\140 & 180 \\\150 & 120 \\\160 & 70 \\\170 & 50 \\\180 & 40\end{array}$$ Calculate (a) the mean height, (b) the variance, (c) the standard deviation, and (d) the standard error of the mean. Plot a rough graph of plant height against frequency. Do the values represent a normal distribution? Based on your calculations, how would you assess the variation within this population?

Two different crosses were set up between carrots (Daucus carota \()\) of different colors and carotenoid content (Santos, Carlos A. F. and Simon, Philipp W. 2002. Horticultura Brasileira 20). Analyses of the \(\mathrm{F}_{2}\) generations showed that four loci are associated with the \(\alpha\) carotene content of carrots, with a broad-sense heritability of \(90 \% .\) How many distinct phenotypic categories and genotypes would be seen in each \(\mathrm{F}_{2}\) generation, and what does a broad-sense heritability of \(90 \%\) mean for carrot horticulture?

Erma and Harvey were a compatible barnyard pair, but a curious sight. Harvey's tail was only \(6 \mathrm{cm}\) long, while Erma's was \(30 \mathrm{cm} .\) Their \(\mathrm{F}_{1}\) piglet offspring all grew tails that were \(18 \mathrm{cm}\) When inbred, an \(\mathrm{F}_{2}\) generation resulted in many piglets (Erma and Harvey's grandpigs), whose tails ranged in \(4-\mathrm{cm}\) intervals from 6 to \(30 \mathrm{cm}(6,10,14,18,22,26, \text { and } 30) .\) Most had \(18-\mathrm{cm}\) tails, while \(1 / 64\) had \(6-\mathrm{cm}\) tails and \(1 / 64\) had \(30-\mathrm{cm}\) tails. (a) Explain how these tail lengths were inherited by describing the mode of inheritance, indicating how many gene pairs were at work, and designating the genotypes of Harvey, Erma, and their 18 -cm-tail offspring. (b) If one of the \(18-\mathrm{cm} \mathrm{F}_{1}\) pigs is mated with one of the \(6-\mathrm{cm}\) \(\mathrm{F}_{2}\) pigs, what phenotypic ratio will be predicted if many offspring resulted? Diagram the cross.
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