Exam 4: Embryogenesis I

Question 1

Embryo

Answer 1

Organism in the early stage of development

Question 2

When is an embryo formed

Answer 2

After syngamy, zygote becomes an embryo

Question 3

Cleavages

Answer 3

Cellular divisions that occur at regular intervals and make cell proliferation and differentiation possible

Question 4

Embryo stages

Answer 4

Cleavage stages
Blastocyst stage
Embryo stage
Fetus stage

Question 5

What are the two cleavage stages

Answer 5

Pre-compacted
Compacted

Question 6

What make mammalian cleavages special

Answer 6

Slowest in the animal kingdom
Follow different patterns (meridional and equatorial - rotational)
Asynchronous (uneven number of cells)
Activate embryonic genome early (within first series of clevages)

Question 7

Steps of pre-attachment development

Answer 7

Ootid –(syngamy)–>
zygote –>
2 cell embryo –(4-8 cell)–>
morula –>
early blastocyst –>
hatching blastocyst –>
hatched blastocyst

Question 8

Where do tight junctions form in the morula

Answer 8

Between the outer cells

Question 9

Where do gap junctions form in the morula

Answer 9

Between the inner cells

Question 10

How does fluid accumulate in the morula

Answer 10

Sodium is pumped into the intracellular spaces by the outer cells and water follows osmotically

Question 11

Affects of fluid accumulation in the early blastocyst

Answer 11

1. The outer cells flatten and form a cavity known as the blastoceole
2. The gap junctions connecting the inner cells of the morula allow cells to polarize as a group
3. Two separate cellular components emerge: inner cell mass (ICM) and trophoblast

Question 12

Oocyte pole

Answer 12

Animal pole: forms at second polar body
Vegetal pole: forms 180 degrees from animal pole

Question 13

Regions and poles of embryo

Answer 13

Dorsal-ventral axis of embryo forms at right angles to animal-vegetal axis
Embryonic pole at 90 degrees from animal pole
Abembryonic pole at 270 degrees
Presumptive dorsal region forms at embryonic pole
Presumptive ventral region

Question 14

Four key genes for production of pluripotency in early blastomeres

Answer 14

Oct3/4
SOX2
c-Myc
Klf4

Question 15

What determines cell fate

Answer 15

Neighboring cells
Might be accomplished via morphogens
Cells acquire polarity

Question 16

Inside and outside hypothesis

Answer 16

Cells in the center will remain undifferentiated, they form the ICM
Cells in the outside will differentiate, they have sticky and non-sticky surfaces

Question 17

Timing of human embryo
Zygote
2-cell
4-cell
Morula
Blastocyst

Answer 17

Zygote: day 1
2-cell: day 1 or 2
4-cell: day 2 or 3
Morula: day 4 or 5
Blastocyst: day 5 or 6

Question 18

What controls early cell divisions

Answer 18

Maternal transcripts (mRNAs)

Question 19

What controls subsequent/later cell divisions

Answer 19

Embryonic transcripts

Question 20

Parthenogenetic development

Answer 20

Development initiated without the contribution of the male genome
Embryos do not reach full development in mammals

Question 21

Epigenesis

Answer 21

Involves heritable but potentially reversible modifications of the DNA, primarily methylation

Question 22

Epigenetic control

Answer 22

Specific properties of individual cells are due to selective expression and repression of genes

Question 23

What are eutherians

Answer 23

Placental mammals

Question 24

Imprinting in placental mammals

Answer 24

Tightly linked to the evolution of the placenta and the maternal investment in fetal development
Many imprinted genes regulate growth, placental development, nutrient transfer

Question 25

Imprinting in marsupials

Answer 25

Less imprinting than placental mammals, but still exists Likely due to similar parent-offspring conflicts over maternal resources

Question 26

What are angiosperms

Answer 26

Flowering plants Examples: arabidopsis, maize

Question 27

Imprinting in flowering plants

Answer 27

Found mostly in the endosperm (nutritive tissue for embryo) reflecting similar conflict over resource allocation from the maternal plant