The nucleosome has an approximate twofold axis of symmetry, called the dyad axis.

TLS Online TPP Program

#Id: 1038

#Unit 5. Developmental Biology

Anencephaly 

a failure of the anterior (rostral) portion of the embryonic neural tube (anterior neuropore) to close properly.

OR

a failure to close the neural tube allows the forebrain to remain in contact with amniotic fluid and subsequently degenerate.

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#Id: 1039

#Unit 5. Developmental Biology

Craniorachischisis-combination of anencephaly with a contiguous bony defect of the spine (also without meninges covering the neural tissue –rachischisis)

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#Id: 1040

#Unit 5. Developmental Biology

The first visible sign of limb development is the formation of bilateral bulges called limb buds.

1. limb bud  is 

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#Id: 1041

#Unit 5. Developmental Biology

The cells that make up the limb bud are derived from the 

1. posterior lateral plate mesoderm

2. adjacent somites

3. bud’s overlying ectoderm

TLS Online TPP Program

#Id: 1042

#Unit 5. Developmental Biology

Limb field - All the cells are capable of forming a limb on their own.

TLS Online TPP Program

#Id: 1043

#Unit 5. Developmental Biology

The positional information needed to construct a limb has to function in a three-dimensional coordinate system:

Proximal-distal axis

Anterior-posterior axis

Dorsal-ventral axis