In mice, the X-linked dominant mutation Testicular feminization (Tfm) eliminates the normal response to the testicular hormone testosterone during sexual differentiation. An XY mouse bearing the Tfm allele on the X chromosome develops testes, but no further male differentiation occurs—the external genitalia of such an animal are female. From this information, what might you conclude about the role of the Tfm gene product and the X and Y chromosomes in sex determination and sexual differentiation in mammals? Can you devise an experiment, assuming you can 'genetically engineer' the chromosomes of mice, to test and confirm your explanation?

Key Concepts

Sex Determination

Sex determination is the biological process that dictates the development of sexual characteristics in an organism. In mammals, this process is primarily influenced by the presence of sex chromosomes, where typically XX denotes female and XY denotes male. The Tfm mutation in XY mice illustrates how genetic factors can disrupt normal sexual differentiation, leading to the development of female external genitalia despite the presence of male chromosomes.

Hormonal Influence on Sexual Differentiation

Hormones play a crucial role in sexual differentiation, particularly during embryonic development. Testosterone, produced by the testes, is essential for male differentiation, promoting the development of male reproductive structures. The Tfm mutation impairs the response to testosterone, highlighting the importance of hormone-receptor interactions in determining sexual phenotype and the development of secondary sexual characteristics.

Genetic Engineering in Research

Genetic engineering involves manipulating an organism's DNA to study gene function and interactions. In the context of the Tfm mutation, researchers could use techniques like CRISPR to modify the Tfm gene or introduce a functional version of the gene into XY mice. This experimental approach would allow scientists to observe changes in sexual differentiation and confirm the role of the Tfm gene product in the process, providing insights into the genetic basis of sex determination.