MB: Reproduction Scientific Skills Exercise

Part A - Understanding the experimental design

In this experiment, scientists inferred how something works normally based on what happened when the normal process was blocked.

What normal process was blocked in Jost's experiment?

hormone production by the embryo’s gonads during development Part B Normally, the gonads of a developing embryo produce hormones during development. How did Jost block this process? Jost removed the portion of each embryo that would form the gonads. Part C - Interpreting the data From Jost's results, what can you infer about the role of the gonads in controlling the development of mammalian genitalia? In the absence of a signal from the male gonads, all embryos develop as female, regardless of whether they are genetically male (XY) or female (XX). Part D - Eliminating alternative hypotheses The data in Jost's experiment could be explained if some aspect of surgery other than gonad removal caused female genitalia to develop. If you were to repeat Jost's experiment, how might you test the validity of this alternative hypothesis? Perform a sham surgery on some embryos. For example, open the embryo but do not remove the gonads. Part E - Making a prediction What result would Jost have obtained if both male and female genital development required signals from the gonads? None of the embryos that had surgery would have developed normal, sexually differentiated genitalia. Part F - Designing a follow-up experiment Jost's experiment showed that the development of male genitalia requires some signal from the male gonads during embryonic development. But is this signal a hormone? To test the hypothesis that the signal is the hormone testosterone, which of the following experiments should you perform? Remove the embryonic gonads and replace them with another source of testosterone. Part G You test the hypothesis that the development of male genitalia normally requires testosterone from the embryonic gonads. You do this by removing the gonads of male (XY) embryos and replacing them with a crystal of testosterone. Which of the following results would support your hypothesis? Male genitalia develop in the rabbits.