Lecture 1

Question 1

2 objectives of development

Answer 1

-generating cellular diversity and order with the individual organisms

-ensuring continuity of life from one gen to the other (fertilization accomplishes this)

Question 2

Development questions (subjects)

Answer 2

Differentiation, pattern formation, morphogenesis, growth, reproduction, environment integration, evolution, regeneration

Question 3

4 stages of embryogenesis

Answer 3

-fertilization
-cleavage
-gastrulation
-organogenesis

Question 4

Fertilization?

Answer 4

Haploid genome (male and female pronuclei) fuse to form diploid genome (zygote)

Question 5

Cleavage?

Answer 5

Embryo starts dividing very rapidly, or goes through many cycles of mitosis

Question 6

Gastrulation?

Answer 6

Blastula forms into 3 germ layers

Question 7

Organogenesis

Answer 7

3 germs layers form of actual organs

Question 8

Cleavage

Why does the oocyte have a large cytoplasmic volume?

Answer 8

Because oocyte requires lots of protein and mRNAs for early development.

Question 9

Cleavage

During cleavage, cytoplasmic is within the zygote starts to divide? Why, and what does it divide into?

Answer 9

It divides to restore proper ratio of cytoplasm to nucleus. Zygote cytoplasm divides into smaller cells called blastomeres. At the end, the blastula is formed.

Question 10

Cleavage

2 parameters that determines cleavage pattern

Answer 10

1. Amount of yolk and its distribution
2. Proteins that are in the egg cytoplasm

Question 11

Cleavage

What is yolk?

Answer 11

It’s the nutrient bearing portion of the oocyte/egg, which supplied food to embryo.

Question 12

Cleavage

How does yolk distribution/amount affect cleavage?

Answer 12

It determines cleavage location and blastomere size.

-presence of yolk = no cleavage

Question 13

Cleavage

How does oocyte proteins affect cleavage?

Answer 13

The proteins dictate angle of mitotic spindle and timing of its formation.

Question 14

Cleavage

Types of egg based on yolk distribution (4)

Answer 14

-isolecithal
-mesolecithal
-telolecithal
-centrolecithal

Question 15

Cleavage

Isolecithal egg?

Answer 15

Yolk is sparse, evenly distributed
(Echinoderm, annelids, mollusks, mammals, nematodes, flatworms)

Question 16

Cleavage

Mesolecithal egg?

Answer 16

Moderate, vegetal yolk distribution (amphibians)

Question 17

Cleavage

Telolecithal egg?

Answer 17

Not uniform distribution of large amount of yolk (fish, reptiles, cephalopod mollusk)

Question 18

Cleavage

Centrolecithal egg?

Answer 18

Yolk = center of egg (most insects)

Question 19

Cleavage

Which pole is zygote nucleus displaced to as yolk grows? Which pole is the yolk located in?

Answer 19

Towards the animal pole. Yolk is located in vegetal pole.

Question 20

Cleavage

Which pole does cleavage occur in?

Answer 20

Animal pole (yolk is in vegetal pole)

Question 21

Cleavage

2 major types of cleavage based on yolk distribution.

Answer 21

-holoblastic cleavage
-meroblastic cleavage

Question 22

Cleavage

Holoblastic cleavage?

Answer 22

-Entire oocyte is divided
-little amount of egg
-Cleavage furrow continues straight through the egg

Question 23

Cleavage

Meroblastic cleavage?

Answer 23

-incomplete cleavage of egg
-large amounts of yolk
-cleavage furrow doesn’t continue straight

Question 24

Cleavage

Which type of cleavage (and pattern (4)) do isolecithal eggs go through?

Answer 24

holoblastic (radical, spiral, bilateral, rotational)

Question 25

Cleavage Which type of cleavage (and pattern (1)) do mesolecithal eggs go through?

Answer 25

-mesolecithal: holoblastic (displaced radical cleavage)

Question 26

Cleavage Which type of cleavage (and pattern (2)) do telolecithal eggs go through?

Answer 26

meroblastic (bilateral, discoidal)

Question 27

Cleavage Which type of cleavage (and pattern (1)) do centrolecithal eggs go through?

Answer 27

meroblastic (superficial)

Question 28

Gastrulation Name the three germs layers.

Answer 28

-endoderm (inner most) -mesoderm (middle layer) -ectoderm (outer layer)

Question 29

Gastrulation Name what each germ layer form into.

Answer 29

-Endoderm: digestive tube, pharynx, respiratory system -mesoderm: inner organs -ectoderm: epidermis, nervous system, neural crest

Question 30

Gastrulation Gastrulation is characterized by two things. What?

Answer 30

-organized migration -movement of 2 different cell types (epithelial and mesenchymal cells)

Question 31

Gastrulation Describe epithelial cells.

Answer 31

-Tightly connected -form sheets -polarized (apical bs basal) -move together

Question 32

Gastrulation Describe mesenchymal cells.

Answer 32

-not tightly connected (loose) -not polarized -free migration

Question 33

Gastrulation How do epithelial cells behave during gastrulation?

Answer 33

Epithelial cells start to lose their connections with each other, becoming mesenchymal cells. This allows them to migrate and becomes the different germ layers.

Question 34

Gastrulation Name 5 patterns of Gastrulation.

Answer 34

-invagination -involution -ingression -delamination -epiboly (Look at pictures for description)

Question 35

Gastrulation When is axis established?

Answer 35

During gastrulation, in the embryo. (Ventral vs dorsal) (anterior vs posterior)

Question 36

Theories of embryo development Name 2, which one is the current theory?

Answer 36

-preformationism -epigenesis (current)

Question 37

Theories of embryo development Describe preformationism.

Answer 37

-17 to 19th century -the idea the organisms develop from miniature, preformed parts -ovism model: preformed parts were present in egg. Sperm triggers development of mini-human. -spermism model: a preformed individual homunculus was present in sperm. Mini human lives inside so arm and helps it to move.

Question 38

Theories of embryo development Describe epigenesis.

Answer 38

-current theory -organs generate from undifferentiated egg cells -Aristotle

Question 39

Theories of embryo development Why the early embryos of such different species looked identical? 2 theories

Answer 39

-Meckel-Serres law: recapitulation (1800s) -Von Baer laws

Question 40

Theories of embryo development Describe Meckel Serres Law: recapitulation

Answer 40

Animals develop from fertilization to gestation/hatching by going through stages of embryogenesis that ressemble its ancestor.

Question 41

Theories of embryo development Describe Von Baer’s laws (4)

Answer 41

1. All developing vertebrates appear very similar right after gastrulation. Only later in development do their distinctive features of class, order, and species emerge. 2. Less general features develop from the more general, until finally the most specialized appear (e.g. early limb development is the same in all vertebrates, only later in development do the differences in legs, wings, and arms emerge). 3. The embryo of a given species, instead of passing through the adult stages of lower animals, departs more and more from them 4. At this phylotypic stage at which embryos of different groups of vertebrates have similar physical structure, there seems to be the least amount of different among the genes expressed by the different groups.