Introduction to Development

Question 1

What is development?

Answer 1

A series of progressive changes in form and function that occurs during an organisms life cycle

Question 2

What are the key stages of development?

Answer 2

Fertilisation
Cleavage
Gastrulation

Question 3

What are the main steps of fertilisation?

Answer 3

One sperm enters the egg

Maternal and paternal genetic material fuse to form a diploid cell

Stimulates cleavage

Question 4

What are the main points of cleavage?

Answer 4

Rapid series of cell division

Produces blastomere

Cells move towards the edge to form a blastula

3 patterns of cleavage

Question 5

What do the cleavage patterns depend on?

Answer 5

Amount of yolk and spindle orientation

Question 6

What are the three cleavage patterns?

Answer 6

Complete

Incomplete - discoidal

Incomplete - superficial

Question 7

How does complete cleavage work?

Answer 7

No yolk = cells divide evenly top to bottom in equal size

Yolk = yolk impedes cleavage furrow and so cells divide asymmetrically and get different sized cells

Question 8

How does incomplete discoidal cleavage work?

Answer 8

Lots of yolk so cleavage furrows don’t penetrate

Blastodisc forms on top of the yolk and forms a membrane

Question 9

How does incomplete superficial cleavage work?

Answer 9

Yolk in the middle

No cytokinesis but get nuclei division

Nuclei migrate to outer edge

Membrane forms around each individual nuclei to form individual cells

Question 10

What is the definition of gastrulation?

Answer 10

Blastula is transformed into embryo with body axis and three tissue layers

Question 12

What are the three tissue layers in gastrulation and what do they form?

Answer 12

Endoderm (inner layer) = gastrointestinal tract and respiratory system

Mesoderm (middle layer) = bone, muscle, heart, kidneys, bladder, reproductive organs and inner skin layer

Ectoderm (outer layer) = outer layer of skin and nervous system

Question 13

How do mitotic spindles attach on radial cleavage?

Answer 13

Spindles form at right angles or parallel to animal-vegetal axis

Forms a regular blastomere pattern

Question 14

How do mitotic spindles attach on spiral cleavage?

Answer 14

Spindles are at oblique angles to a-v axis

Get spiral blastomere pattern

Question 15

How do mitotic spindles attach on rotational cleavage?

Answer 15

1st division = parallel to a-v axis

2nd division = right angles

Get disordered/rotational pattern

Question 16

What is organogenesis?

Answer 16

Formation of organs and organ systems

Get development of body segments

Question 17

What do somites produce?

Answer 17

Vertebrae, ribs, trunk and limb muscles

Question 18

What do neural crest cells produce?

Answer 18

Peripheral nerves (connect to spinal cord)

Question 19

What is neurulation?

Answer 19

Occurs in early organogenesis

Begins formation of nervous system in vertebrates

Question 20

Basics of neurulation?

Answer 20

Ectoderm and neural plate thicken

Ridges on neural plate form

Forms a groove

Ridges fuse over top to form a neural tube

Question 21

What are the basics of gastrulation in mammals?

Answer 21

Blastula forms trophoblasts and inner cell mass

Trophoblasts form placenta

Inner cell mass forms epiblast and hypoblast

Epiblast forms future embryo

Hypoblast forms extra embryonic membranes

Epiblast and hypoblast formed in blastocyst

Blastocyst implants itself into uterus

Question 22

What are the basics of gastrulation in birds?

Answer 22

Starts when Henson’s node moves anterior to posterior - gives brain longer to develop

Movement down body axis forms primitive streak

Cells migrate to primitive streak

Question 23

What are the basics of gastrulation in sea urchins?

Answer 23

Blastomere invaginates

Primary mesenchyme cells migrate to invagination

These become mesoderm cells

Then become archenteron

Secondary mesenchymal cells attach to archenteron and pull it up

Mouth forms at blastopore

Question 24

What are the importance of extra embryonic membranes in birds?

Answer 24

Support the embryo

Develop from germ layer

Yolk sac = for nutrient transfer via blood vessels

Amniotic sac = outer layer which provides protection

Chorion = for gas/water transfer and limits water loss

Allantois = stores metabolic waste