Two genes may share some related exons but also have unique exons.

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#Id: 4735

#Unit 5. Developmental Biology

In C. elegans

When sperm fuses with the egg cell membrane, polyspermy is prevented by the rapid synthesis of chitin by the newly fertilized egg.

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#Id: 4736

#Unit 5. Developmental Biology

The zygote of C. elegans exhibits rotational holoblastic cleavage.

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#Id: 4737

#Unit 5. Developmental Biology

During early cleavage, each asymmetrical division produces:

• One founder cell (denoted AB, E, MS, C, and D) that produces differentiated descendants
• One stem cell (the P1–P4 lineage) 

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#Id: 4738

#Unit 5. Developmental Biology

The anterior-posterior axis is determined before the first cell division, and the cleavage furrow is located asymmetrically along this axis of the egg, closer to what will be the posterior pole.

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#Id: 4739

#Unit 5. Developmental Biology

The stem cell lineage always undergoes meridional ,division to produce

(1) An anterior founder cell (AB)

(2) A posterior cell (P1) that will continue the stem cell lineage.

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#Id: 4740

#Unit 5. Developmental Biology

The founder cell (AB) divides equatorially, while the P1 cell divides meridionally (transversely) to produce another founder cell (EMS) and a posterior stem cell (P2).