5. Among the native Americans, two types of earwax are seen, dry and sticky. A g

Question

5. Among the native Americans, two types of earwax are seen, dry and sticky. A geneticist studied the inheritance of this trait by observing the types of offspring produced by different kinds of matings. He observed the following numbers: (2.0pts.)

Parents                            number of mating pairs                 offspring

                                                                                                Sticky           Dry

Sticky x Sticky                           10                             32               6

Sticky x Dry                                8                               21              9

Dry x Dry                                   12                              0                42

a) How is earwax type inherited?

b) Why are there no 3:1 or 1:1 ratios in the data shown in the chart?

Explanation / Answer

a) A cross between dry x dry produces only sticky ones. Therefore, dry appears to be recessive to sticky. A Sticky X Sticky cross yields some dry ones. This tells the parents are not pure breeds. Therefore, it appears that it is a simple dominant or recessive Mendelian inheritance.

b) We do not know the genotypes of the parents. They may be mixed up genotypes. In order to get Mendelian ratios of 1:1 or 3:1, true breeding lines or individuals with known genotypes are needed. Probably this is the reason we did not get Mendelian ratios.

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