FORM & FUNCTION (Gastrulation)

Question 1

Gastrulation:

Answer 1

-process of formation of germ layers
-a single layered blastula is converted into a trilaminar structure containing the outer ectoderm, middle mesoderm, and the inner endoderm

Question 2

Blastoderm layers (chicken):

Answer 2

-area opaca
-area pellucida

Question 3

Area pellucida (chicken):

Answer 3

-gives rise to the upper epiblast and lower hypoblast

Question 4

Lower hypoblast (chicken):

Answer 4

-becomes the extra-embryonic endoderm

Question 5

Forming the ‘primitive streak’ (chicken):

Answer 5

-from thickening of the blastoderm by the convergence of cells in the surface of the blastoderm towards the midline

Question 6

Primitive node or Hensen’s node:

Answer 6

-formed from an increased concentration of cells in the cranial end

Question 7

Formation of primitive streak and primitive node:

Answer 7

-establish the cranial-caudal axis and the right and left sides

Question 8

Primitive groove formed from:

Answer 8

-cells of the epiblast converging on the primitive streak ingress into space between epiblast and hypoblast

Question 9

Migrating epiblast cells (mes-endoderm cells/intermediate cell type):

Answer 9

1. Make contact with the hypoblast and form the endoderm
2. Some continue to migrate and elongate (mesoderm/mesenchymal cells)

Question 10

Endoderm formation:

Answer 10

-migrating cells from epiblast make contact with hypoblast, replaces the hypoblast and forms the embryonic endoderm
-ingression and cell migration downwards and inwards continues

Question 11

Mesenchymal cells:

Answer 11

-the cells of the epiblast that migrate through the primitive streak, elongates and gain the capability to migrate and differentiate
-intra-embryonic mesoderm and extra-embryonic mesoderm

Question 12

Intra-embryonic mesoderm:

Answer 12

-those that stay between the endoderm and epiblast
-will become the organism

Question 13

Extra-embryonic mesoderm:

Answer 13

-mesenchymal cells that migrate further laterally between hypoblast and trophectoderm
-will become the extra embryonic membranes

Question 14

What gives rise to the ectoderm:

Answer 14

-elongated, migratory epiblast cells (bottle cells, due to its shape)

Question 15

Mammalian gastrulation and germ layer formation resembles:

Answer 15

-that of a chicken

Question 16

Notochord:

Answer 16

-both the primitive streak and primitive node recede, and is replaced by a notochord
-prominent midline structure composed of epiblast cells which have migrated through the cranial most portion of the primitive nodes (primitive node)
-eventually spans the entire length of the embryo
-not retained in many species

Question 17

Left-right symmetry in vertebrates:

Answer 17

-developed during gastrulation
-genes (lv) transcription factors and proteins are involved
-defects or absence of some of these elements cause developmental anomalies
Ex. mutations in Iv

Question 18

lv:

Answer 18

-situs inversus viscerum
-left, nodal

Question 19

Snail:

Answer 19

-gene for right side development

Question 20

Gene expression on left side development:

Answer 20

-leftward flow
-Fgf-8 promotes nodal and lefty-2
>activates left side formation genes and inhibits right side formation genes (ex. snail)

Question 21

mutations in lv results in:

Answer 21

-random placement of organs on either side of the left hand axis
*lethal anomaly

Question 22

Twinning:

Answer 22

-two individuals developed in same pregnancy
-dizygotic and monozygotic

Question 23

Dizygotic:

Answer 23

-2 oocytes, from 2 different ovarian follicles, fertilized by 2 different spermatozoa

Question 24

Monozygotic:

Answer 24

Monozygotic:
-single oocyte fertilized by single spermatozoa
-2 ways
1. Twinning occurs at 2 blastomere stage, where each one giving rise to an embryo/individual with separate fetal membranes
2. Duplication of the inner cell mass

Question 25

Incidence of twinning in domestic animals depends on species and breed:

Answer 25

-cattle: 2-3%
-sheep: 2-5%
-horses: up to 30%
*conjoined twins in cattle: 1 in 100,000 births

Question 26

Production of gastrulation=gastrula

Answer 26

-a pear shaped embryo
>3 germ layers
>column of mesoderm
>notochord (oriented in cranial to caudal axis)
>relative to notochord, the embryo has a right and left side