Developmental Biology

Question 1

Define regional specification

Answer 1

Assigning a cell a particular cell type to become

Question 2

Define differentiation

Answer 2

Instructing the cell to form the functional characteristics of that cell type

Question 3

What are the three reproductive strategies?

Answer 3

Oviparity
Oviviparity
Viviparity

Question 4

Define oviparity

Answer 4

• Eggs laid with little/no embryonic development in mother
• Internal/external fertilisation
• Invertebrates/fish/amphibians/reptiles/birds/monotreme mammals (eg. Echidna)

Question 5

Define oviviparity

Answer 5

• Eggs retained until ready to hatch.
• No placental connection
• Internal fertilisation, live young
• Invertebrates/fish/amphibians

Question 6

Define viviparity

Answer 6

• Eggs retained and connected via placenta
• Internal fertilisation, live young
• Most mammals, rare in invertebrates/fish/reptiles

Question 7

What reproductive strategy do marsupials use?

Answer 7

Viviparity, although they are born in a very immature state and lack a complex placenta

Question 8

What is the recurrent laryngeal nerve?

Answer 8

A branch of the vagus nerve

Innervates the larynx

Question 9

What is the larynx and it’s function?

Answer 9

• Formed of 9 cartilages and supporting tissues

* Speech, breathing, preventing food from entering trachea

Question 10

What do the superior laryngeal nerves innervate?

Answer 10

Glottis
Laryngeal vestibule
Cricothyroid muscle

Question 11

Describe the superior and recurrent laryngeal nerves

Answer 11

Superior are direct from vagus to larynx

Inferior loop around large artery in thorax- left aortic arch, right subclavian artery

Question 12

Why do the recurrent laryngeal nerves loop around arteries?

Answer 12

• Superior laryngeal nerves innervate 4th pharyngeal arches
• Recurrent innervate 6th
• The vasculature of the arches is reorganised to form the major arteries of the thorax and neck
• Recurrent nerves remain trapped under thoracic arteries so extend down to thorax

Question 13

How common is it for the right recurrent nerve to not be recurrent? Why does it happen?

Answer 13

1/200

Changes to arrangement of right subclavian artery

Question 14

How common are birth defects in England and Wales?

Answer 14

1%

Cleft lip and palate most common

Question 15

What is the last common ancestor of bilateral animals?

Answer 15

Urbilateria
Three germ layers
Anterior/posterior, dorsal/ventral and left/right

Question 16

What do HOX genes, PAX6 and Chordin/BMP do?

Answer 16

Genetic toolkits
• HOX- anterior/posterior patterning
• PAX6- eye development
• Chordin/BMP- neural development

Question 17

What is aniridia and it’s cause?

Answer 17

Eye defects including lack of iris

Heterozygous, loss of function PAX6 mutations

Question 18

What happens to mice homozygous for loss of function PAX6 mutations?

Answer 18

Die in utero

No eyes, severe facial defects

Question 19

How would you produce ectopic eyes?

Answer 19

PAX6 expression in other parts of brain

Question 20

What’s the link between PAX6 and the drosophila eyeless gene?

Answer 20

Same function
Share 90% amino acid sequence identity
-> orthologues (same gene different animals)

Question 21

What are preformation and epigenesis?

Answer 21

Preformation- theory that embryos already have their structure they just increase in size
Epigenesis- complexity increases with time

Question 22

What are the three types of cleavage and what do they result in?

Answer 22

• Holoblastic- egg fully cleaved
mammals/amphibians/nematodes
• Meroblastic- only yolk free portion cleaved
Chick/zebra fish
• Superficial- only yolk free outer layer cleaved
Drosophila
—> blastomere

Question 23

How is a blastula formed?

Answer 23

Cavity appears in centre of blastomere during holoblastic cleavage divisions- blastocoel
Embryo is now blastula and rate of cell division slows

Question 24

What is gastrulation?

Answer 24

Single layered blastula converted to triplonlastic gastrula. Germ layers:
• Ectoderm-> skin, nervous system
• Mesoderm-> muscles, connective tissue, urogenital system
• Endoderm-> epithelial tissues of gut

Question 25

What happens after gastrulation?

Answer 25

• Neurulation- part of ectoderm moves inside endoderm to form nervous system

Question 26

What is the phylotypic stage?

Answer 26

Embryo has acquired the body plan shared with all other organisms in the same phyla

Question 27

What are determinants in eggs?

Answer 27

• Mainly Establish polarities
• Some localised determinants establish specific cell types:
-Drosphila germplasm- germ cells
-Ascidian myoplasm- muscle

Question 28

What are ascidians?

Answer 28

• Marine invertebrate filter feeders
• Phylum- Chordata (with vertebrates)
• Hermaphrodites- but don’t fertilise own eggs
• Holoblastic cleavage divisions (1st and 2nd vertical but smaller posterior. 3rd horizontal)
• Eggs contain different coloured cytoplasms later associated with specific cell types

Question 29

What cell type does ascidian yellow cytoplasm form and why?

Answer 29

Muscle

Contains macho-1 mRNAs which encode a putative zinc-finger transcription factor

Question 30

What are blastomeres responsible for in ascidian development?

Answer 30

• A particular set of larval tissues, even in isolation

* Autonomous development

Question 31

What is embryonic regulation?

Answer 31

• Ability of an embryo to develop normally when portions are removed/rearranged
• Responsible for monozygotic twins

Question 32

Define embryonic induction

Answer 32

Cell signalling affecting development of responding cells

Question 33

Define cell competence

Answer 33

Ability of a cell to respond to an inductive signal

Question 34

What are the four stages of potency?

Answer 34

Totipotent- all cell types
Pluripotent- all embryonic cell types
Multipotent- many embryonic
Unipotent- only one cell type