Question

The identification and characterization of genes that control sex determination has been a focus of investigators working with \(C .\) elegans. As with Drosophila, sex in this organism is determined by the ratio of \(X\) chromosomes to sets of autosomes. A diploid wild-type male has one \(X\) chromosome and a diploid wild-type hermaphrodite has two X chromosomes. Many different mutations have been identified that affect sex determination. Loss- of-function mutations in a gene called her-1 cause an XO nematode to develop into a hermaphrodite and have no effect on \(\mathrm{XX}\) development. (That is, \(\mathrm{XX}\) nematodes are normal hermaphrodites.) In contrast, loss- offunction mutations in a gene called tra-I cause an XX nematode to develop into a male. Deduce the roles of these genes in wild-type sex determination from this information.

Short answer

Answer: In wild-type sex determination for C. elegans, the her-1 gene is responsible for promoting male development (XO), while the tra-I gene promotes hermaphrodite development (XX).

Step-by-step solution

Understanding wild-type sex determination

In wild-type sex determination, a diploid male has one X chromosome (XO), and a diploid hermaphrodite has two X chromosomes (XX). We will now analyze the effects of the mutations to interpret the normal roles of the her-1 and tra-I genes.

Understanding the effects of her-1 mutation

In the case of her-1 gene loss-of-function mutations, an XO nematode develops into a hermaphrodite. This means that, in wild-type conditions, the her-1 gene must promote male development when it is functional. Thus, the her-1 gene is responsible for male development in wild-type nematodes.

Understanding the effects of tra-I mutation

In the case of tra-I gene loss-of-function mutations, an XX nematode develops into a male. This means that, in wild-type conditions, the tra-I gene must prevent male development (promoting hermaphrodite development) when it is functional. Thus, the tra-I gene is responsible for hermaphrodite development in wild-type nematodes.

Deduce the roles of her-1 and tra-I in wild-type sex determination

Based on our analysis of the effects of the mutations in her-1 and tra-I gene, we can deduce that: - The her-1 gene promotes male development in wild-type conditions (XO). - The tra-I gene promotes hermaphrodite development in wild-type conditions (XX). In conclusion, the wild-type roles of her-1 and tra-I genes in sex determination are that the her-1 gene is responsible for male development, and the tra-I gene is responsible for hermaphrodite development.