Question 1

How are the major body axes established during C. elegans embryonic development?

Accepted Answer

During C. elegans development, three major axes form sequentially. The anterior-posterior axis is established during the first asymmetrical cell division after fertilization. The dorso-ventral axis forms between the two-cell and four-cell stages, and the left-right axis appears shortly after the four-cell stage. These axes establish the basic body plan that guides all subsequent development.

Question 2

What are the six founder cells in C. elegans and what tissues do they produce?

Accepted Answer

Six founder cells—AB, MS, E, C, D, and P4—appear during the first five cell divisions and always generate the same tissues in every worm. AB produces neurons and pharynx; MS generates muscle, pharynx, and neurons; E becomes intestinal tissue; C forms muscle, neurons, and skin; D produces body wall muscle; and P4 gives rise to the germline, which is essential for reproduction.

Question 3

Why is apoptosis important in C. elegans development?

Accepted Answer

Apoptosis, or programmed cell death, is a critical developmental process in C. elegans. During embryogenesis, 113 cells die through apoptosis, selectively removing specific cells to shape tissues and organs. This process is conserved across many organisms, including humans, making C. elegans a valuable model for understanding how apoptosis regulates development and tissue formation.

Question 4

What are the larval stages of C. elegans and what is the dauer stage?

Accepted Answer

C. elegans has four larval stages—L1, L2, L3, and L4—followed by adulthood. Under stressful conditions like food scarcity, late L1 or L2 larvae enter an alternative developmental program called the dauer stage. Dauers can remain arrested for months and resume normal development when food becomes available, making this stage important for understanding larval arrest in parasitic nematodes.

Question 5

How do hermaphrodites and males differ in C. elegans?

Accepted Answer

C. elegans has two sexes: self-fertilizing hermaphrodites and males. Hermaphrodites are wider and longer with a pointed tail, producing both oocytes and sperm. Males are slim-bodied with a distinctive copulatory tail and produce only sperm. Occasionally, nondisjunction in the hermaphrodite germline produces males with one sex chromosome instead of two.

Question 6

How is reproduction primarily achieved in C. elegans populations?

Accepted Answer

Self-fertilization is the primary reproductive mode in C. elegans, with hermaphrodites producing genetically identical hermaphrodite progeny through self-fertilization. Although sexual reproduction occurs at low frequency through mating with males, self-fertilization dominates in nature. This reproductive strategy contrasts with development and reproduction in other model organisms and raises questions about why males persist evolutionarily.

Question 7

What are the key steps for setting up a successful genetic cross in C. elegans?

Accepted Answer

To set up a genetic cross, prepare multiple plates with concentrated bacterial spots and label them with strain names and dates. Place three L4 or young adult hermaphrodites and twelve L4 or young adult males on each plate. Incubate at the appropriate temperature and check after four days for cross progeny. Approximately 50% males indicates successful crossing; pick L4 hermaphrodite progeny to verify the expected phenotype.

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