Devo Lect 6 - Cleavage Flashcards

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1
Q

Blastomeres

A

“sprouting part” - name after zygote divides

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2
Q

Cell divisions and cycle

A

Stored proteins, mRNA; Cell cycle - M, S, M, S (fast!) - get smaller

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3
Q

Patterns of cleavage

A

Holoblastic (“entire sprouting” - cell division in whole organism) and Meroblastic (“part sprouting” - incomplete cell division)

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4
Q

Holoblastic cleavage subtypes*

A

Isolecithal “equal amounts of yolk” (radial - echinoderms; spiral - annelids, molluscs; rotational - humans, nematodes) and Mesolecithal “moderate amounts of yolk” (amphibians)

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5
Q

Meroblastic cleavage subtypes*

A

Telolecithal “yolk more on one side” (bilateral - cephalopod; discoidal - fish, reptiles, birds) and centrolecithal “yolk in middle” (superficial - insects)

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6
Q

Sea urchin cleavage

A

isolecithal - synchronous, radial (divides x, y then z); cells get smaller; divides to form Blastula larva: hollow sphere containing water and salts in blastocoel - higher osmotic pressure draws in water - SA/V ratio increases

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7
Q

Blastocoel

A

Hollow space inside developing sea urchin embryo containing solutes and draws in water; space where organs will develop

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8
Q

Importance and differences of mesolecithal cleavage

A

It has more yolk, so the frog embryo can divide and grow longer in the egg; still synchronous, radial; blastocoel is smaller; unequal sizes, smaller ones around blastocoel (animal pole)

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9
Q

Formation of gray crescent in amphibians

A

Caused by cytoplasm movement (microtubules); first cell division bisects gray crescent

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10
Q

Hans Spemann experiment

A

Took a human hair and put it around an amphibian egg along the axis of the first division and separated them, developed into two embryos; second time split with gray crescent on only one side, one developed normal, the other was a ball. Asymmetry of the fertilized egg!

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11
Q

Spiral holoblastic cleavage

A

Some worms, most molluscs, snails. Blastomeres divide at angles, cause a spiral. Can be left (sinistral) or right handed (dextral)! No blastocoel = stereoblastula

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12
Q

Nodal

A

Molecule that determines left/right symmetry in development

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13
Q

Rotational holoblastic cleavage

A

Mammals; little yolk because it will implant and gain nutrients

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14
Q

Why hard to study human cleavage?

A

Small eggs; fewer eggs; internal development (but can be done in dish)

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15
Q

Differences between mammalian and sea urchin/amphibian frogs

A

Very slow cleavage (24h vs 30 mins), still have G1 and G2; first division same, second one different (one in Z plane, one in Y); asynchronous; zygotic transcription happens early; compaction

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16
Q

Compaction

A

In mammals; Occurs around 8 cell stage; connections change between them so it looks like they squish together (via cell adhesion molecules); communication (gap junctions) increases;

17
Q

Mammalian cleavage - where

A

Cleavage occur in oviduct and uterus. Ovary isn’t completely attached to oviduct btw;

18
Q

Explain fig 11.20! Ovulation to implantation**

A

Ovulation (FSH); release egg and follicular fluid (Rantes, progesterone); sperm translocation; slow in isthmus (cilia); capacitated; fertilization occurs usually in ampulla; egg moves and divides; becomes morula, then blastocyst; hatching (strypsin); early implantation (collagenases)

19
Q

Timescale for human cleavage

A

Day 0 - fertilized; Day 1 - 2 cells; Day 3/4 - at isthmus - Morula stage; Day 5-7 - blastocyst

20
Q

Compare sea urchin embryo and human embryo **

A

Sea urchin: all cells divide in X, Y then Z; humans divide in X, then one divides in Y and the other in Z (roational); much slower and asynchronous; genome activated during cleavage; compaction

21
Q

Morula

A

a solid ball of cells resulting from division of a fertilized ovum, and from which a blastula is formed