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.

Key concepts

C. elegans

C. elegans, short for Caenorhabditis elegans, is a small, transparent worm that has gained popularity as a model organism in genetic studies. These worms are particularly useful in research for understanding various biological processes, including sex determination.
In C. elegans, sex is determined by the number of X chromosomes in relation to sets of autosomes. A single X chromosome (XO) leads to the development of a male, while two X chromosomes (XX) result in a hermaphrodite. Hermaphrodites have the ability to produce both eggs and sperm, which allows them to self-fertilize.
C. elegans is a simple organism, but its genetic makeup is surprisingly rich, making it an ideal candidate for studying genetic mutations and their impacts on sex determination.

her-1 gene

The her-1 gene in C. elegans is crucial for determining the sex of the organism. It plays a pivotal role in promoting male development. In wild-type nematodes, a functional her-1 gene ensures that XO individuals develop into males.
When the her-1 gene undergoes a loss-of-function mutation, its ability to support male development is compromised. As a result, an XO nematode with a non-functioning her-1 gene will develop as a hermaphrodite instead of a male. This indicates that the her-1 gene is a key promoter of male characteristics in C. elegans under normal conditions.
The study of the her-1 gene helps researchers understand how genes control sexual development and contribute to the larger field of genetics and developmental biology.

tra-I gene

The tra-I gene in C. elegans is essential for promoting hermaphrodite development under wild-type conditions. It works by inhibiting male development in organisms that are genetically determined to become hermaphrodites (XX).
If there is a loss-of-function mutation in the tra-I gene, the organism modifies its developmental pathway. Instead of becoming a hermaphrodite, an XX nematode will develop into a male. This starkly contrasts with its typical role, highlighting the gene's function in discouraging male characteristics in environments where two X chromosomes are present.
By exploring the tra-I gene, scientists can gain insights into how the absence or presence of certain genes influences sexual development, opening doors to broader understanding in the realm of genetic research.

Genetic Mutations

Genetic mutations refer to changes in the DNA sequence of an organism, which can result in alterations in gene function and the organism's phenotype. Such mutations are often critical in understanding genetic diseases and developmental processes in model organisms like C. elegans.
In the context of sex determination in C. elegans, mutations in genes like her-1 and tra-I provide valuable information about their roles. By observing the phenotypic outcomes of these mutations, researchers can map the gene's function in normal sex development.
Studying genetic mutations not only aids in understanding very specific biological processes but also paves the way for advancements in genetic engineering and biotechnology. It also provides a framework for further investigation into the molecular mechanisms behind sex differentiation and development.