# Monohybrid - Page 1 of 3 Monohybrid Crosses Problems...

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Page 1 of 3 Monohybrid Crosses – Problems, Problems, Problems Chapters 1-4 1. The mode of inheritance for plum eyes: this mutant is dominant to wild-type; is autosomal; and lethal when homozygous. In cross 1, the genotype of the plum-eyed female is EE + and the genotype of the wild-type or red-eyed male is E + E + . In cross 2, the red-eyed female is E + E + and the plum-eyed male is EE + . In cross 3, both red-eyed male and female parents have genotype E + E + . Finally in cross 4, both plum-eyed male and female parents have genotype EE + . The following chi square goodness of fit to test Ho that F 2 data of cross 4 fit 2/3 plum to 1/3 red is as follows: Classes Observed # Expected # O – E (O – E) 2 (O – E) 2 /E Plum 610 667 -57 3249 4.871 Red 390 333 +57 3249 9.757 TOTAL 1,000 1,000 0 ----------- X 2 = With 1 degree of freedom and a chi square value equal to 14.628, probability is less than 0.001, and you would reject your hypothesis as stated. However, this does not mean that the genetic explanation for mode of inheritance is incorrect. Rather it may indicate mis-identification of plum eyes in contrast to wild-type. The experiment should be repeated again, and the phenotypes more carefully scored. Only if the results are consistently the same would you consider another alternative explanation. 2. Yes, you can combine the male and female data for each generation of each cross since there are no differences between them. The mode of inheritance for shaven bristles: is recessive to wild- type bristles; is autosomal; and is non-lethal. The parental genotypes for the first cross are bb for females with shaven bristles and b + b + for males with wild-type bristles. The reciprocal cross is

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Monohybrid - Page 1 of 3 Monohybrid Crosses Problems...

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