distribution (i.e., many individuals have intermed iate trait values, and relati
ID: 136029 • Letter: D
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distribution (i.e., many individuals have intermed iate trait values, and relatively few have extreme trait values). 70 60 50 bell curve The reason quantitative traits often approxi mate a normal distribution is related to the idea 30 of gene product "dosage" as described in the pre20b lab. If each locus is contributing a certain dosage 10 of product to the phenotype, and individuals vary in which alleles they have, there are a lot of possible combinations in the population. Q.1 02 0.3 04 05 06 07 08 09 Phenotype Why are very small and very large organisms relatively rare? These organisms occur only at the tails of a normal distribution where their frequency is quite low. For very small organisms, all, or almost all, of their all gene products. For very large organisms, all, or almost all, of their alleles contribute high doses of gene products. Thin frequency of matings between suitable parents eles contribute low doses of k about the genotypes of parents that could produce these kinds of offspring and the Very small or very large offspring could only be produced by a mating between two parents wh had almost all alleles of this type. Matings such as these would be rare in a random They are much more likely to occur in a "like-with-like" matings). that is Why average-sized organism possesses a combination of alesfor low doses ofthe gene product and high doses of the gene product. A great many kinds of matings could produce offspring of this type. For example, some offspring of average size would occur when a large organism mated with a small organism, or when two average- are average-sized organisms the most common, or the most frequent, in a population? An produced would be those between two extremely large or two extremely small parents. Describe in your own words, how you know that thorax length in Drosophila is a quantitative trait: (0. points) Of the traits below, underline those likely to be quantitative traits eye color in fruit flies, leg length in grasshoppers, body weight in dairy cows, human blood type (A, B, O), cail length in mice. (0.75 points) 143Explanation / Answer
Why thorax length in Drosophila is a quantitative trait:
Explanation: The classical Mendelian traits are qualitative in nature. Therefore these traits are grouped into distinct phenotypes. These distinct phenotypes are controlled by only one gene or a very few genes and these traits are not modified by environmental factors.
Whereas quantitative traits are those that exhibit continuous variation and can usually be quantified by counting, measuring, weighing and so on. These traits are controlled by many genes and each gene exerts a small additive effect (i.e.effect of the genes are cumulative). These traits can also be modified by environmental factors.
In quantitative traits, there is no dominance, no gene interaction and no linkage.
Hence traits such as body weight gains, mature plant heights are quantitative traits.
Now, as the thorax length in Drosophila shows a continuous variation in it and it is controlled by more than one genes and there is an influence of environmental factors on this trait. Therefore, thorax length in Drosophila is a quantitative trait.
Among eye color in fruit flies, leg length in grasshoppers, body weight in dairy cows, human blood type(A, B, O), tail length in mice quantitative traits are leg length in grasshoppers, body weight in dairy cows, tail length in mice because of the same reason.
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