*18. For each of the following characteristics, indicate whether it would be considered a discontinuous characteristic or a quantitative characteristic. Briefly justify your answer.
(a) Kernel color in a strain of wheat, in which two codominant alleles segregating at a single locus determine the color. Thus, there are three phenotypes present in this strain: white, light red, and medium red.
(b) Body weight in a family of Labrador retrievers. An autosomal recessive allele that causes dwarfism is present in this family. Two phenotypes are recognized: dwarf (less than 13 kg) and normal (greater than 13 kg).
(c) Presence or absence of leprosy; susceptibility to leprosy is determined by multiple genes and numerous environmental factors.
(d) Number of toes in guinea pigs, which is influenced by genes at many loci.
(e) Number of fingers in humans; extra (more than five) fingers are caused by the presence of an autosomal dominant allele.
*19. The following data are the numbers of digits per foot in 25 guinea pigs. Construct a frequency distribution for these data. 4,4, 4, 5, 3, 4, 3,4, 4, 5, 4,4, 3, 2,4,4, 5, 6,4, 4, 3,4, 4,4, 5
20. Ten male Harvard students were weighed in 1916. Their weights are given in the following table. Calculate the mean, variance, and standard deviation for these weights.
Weight (kg) of Harvard students (class of 1920)
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