Chapter 20: Problem 10
List as many human traits as you can that are likely to be under the control of a polygenic mode of inheritance.
Chapter 20: Problem 10
List as many human traits as you can that are likely to be under the control of a polygenic mode of inheritance.
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Get started for freeHeight in humans depends on the additive action of genes. Assume that this trait is controlled by the four loci \(R, S, T,\) and \(U\) and that environmental effects are negligible. Instead of additive versus nonadditive alleles, assume that additive and partially additive alleles exist. Additive alleles contribute two units, and partially additive alleles contribute one unit to height. (a) Can two individuals of moderate height produce offspring that are much taller or shorter than either parent? If so, how? (b) If an individual with the minimum height specified by these genes marries an individual of intermediate or moderate height, will any of their children be taller than the tall parent? Why or why not?
In an assessment of learning in Drosophila, flies were trained to avoid certain olfactory cues. In one population, a mean of 8.5 trials was required. A subgroup of this parental population that was trained most quickly (mean \(=6.0\) ) was interbred, and their progeny were examined. These flies demonstrated a mean training value of \(7.5 .\) Calculate realized heritability for olfactory learning in Drosophila.
In a herd of dairy cows the narrow-sense heritability for milk protein content is \(0.76,\) and for milk butterfat it is \(0.82 .\) The cor- relation coefficient between milk protein content and butterfat is \(0.91 .\) If the farmer selects for cows producing more butterfat in their milk, what will be the most likely effect on milk protein content in the next generation?
In a cross between a strain of large guinea pigs and a strain of small guinea pigs, the \(F_{1}\) are phenotypically uniform, with an average size about intermediate between that of the two parental strains. Among $1014 \mathrm{F}_{2}$ individuals, 3 are about the same size as the small parental strain and 5 are about the same size as the large parental strain. How many gene pairs are involved in the inheritance of size in these strains of guinea pigs?
A strain of plants has a mean height of \(24 \mathrm{cm} .\) A second strain of the same species from a different geographical region also has a mean height of \(24 \mathrm{cm}\). When plants from the two strains are crossed together, the \(F_{1}\) plants are the same height as the parent plants. However, the \(\mathrm{F}_{2}\) generation shows a wide range of heights; the majority are like the \(P_{1}\) and \(F_{1}\) plants, but approximately 4 of 1000 are only $12 \mathrm{cm}\( high, and about 4 of 1000 are \)36 \mathrm{cm}$ high. (a) What mode of inheritance is occurring here? (b) How many gene pairs are involved? (c) How much does each gene contribute to plant height? (d) Indicate one possible set of genotypes for the original \(\mathrm{P}_{1}\) parents and the \(\mathrm{F}_{1}\) plants that could account for these results. (e) Indicate three possible genotypes that could account for \(\mathrm{F}_{2}\) plants that are \(18 \mathrm{cm}\) high and three that account for \(\mathrm{F}_{2}\) plants that are \(33 \mathrm{cm}\) high.
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