Development 1: Zygote to organism

Question 1

Define development

Answer 1

Series of progressive changes in form and function that occurs during an organism’s life cycle

Question 2

What does development continue until?

Answer 2

Death

Question 3

What are the 5 key stages of development?

Answer 3

1. Fertilisation
2. Cleavage
3. Gastrulation
4. Organogenesis
5. Morphogenesis

Question 4

What is fertilisation?

Answer 4

1 sperm enters egg.
- inside paternal and materinal genetic material fuse = diploid cell
- stimulates cleavage

Question 5

Which parent do the cytoplasm and mitochondria of the zygote come from?

Answer 5

Mother

Question 6

Which hemisphere is the nucleus in (in most species)?

Answer 6

animal hemisphere

Question 7

Which hemisphere do nutrients accumulate?

Answer 7

Vegetal hemisphere

Question 8

In what class does the ‘grey crescent’ appear?

Answer 8

Amphibians

Question 9

Describe the grey cresent

Answer 9

• In amphibians sperm enters the animal hemisphere, the cortex rotates exposing the grey crescent
• Proteins in the grey crescent control what form the cells will take

Question 10

What is cleavage?

Answer 10

Rapid series of cell divisions

Question 11

What is each cell produced during cleavage called?

Answer 11

Blastomere

Question 12

How many patterns of cleavage are there, and what are they?

Answer 12

Complete
Incomplete-discoidal
Incomplete-superficial

Question 13

What does cleavage pattern depend on?

Answer 13

Species dependent:
- Depends on amount of yolk and orientation of spindles

Question 14

Describe complete cleavage

Answer 14

No yolk = all cells are equal size e.g sea urchins
Yolk gets in the way of the cleavage furrow = cells divide asymmetrically e.g frogs

Question 15

Describe incomplete cleavage - discoidal

Answer 15

• With lots of yolk the cleavage furrows don’t penetrate the yolk = cleavage is incomplete
• A blastodisc forms on top of the yolk
  E.g birds

Question 16

Describe incomplete cleavage - superficial

Answer 16

• Nucleus divides but cytokinesis doesn’t occur
• Nuclei migrate to the edge & membrane grows inward = nuclei partitioned into individual cells
  E.g insects

Question 17

Describe radial cleavage

Answer 17

mitotic spindles form at right angles/ parallel to animal- vegetal axis

Question 18

Describe spiral cleavage

Answer 18

Mitotic spindles are oblique angles (diagonal) to a a-v axis

Question 19

Describe rotational cleavage

Answer 19

first division is parallel to a-v axis, second is at right angles = ‘disorderly’ arrangement of daughter cells

Question 20

Early in development cells can be described as ________

Answer 20

totipotent

Question 21

define totipotent

Answer 21

any cell can become any cell type

Question 22

What is determination

Answer 22

When a cells fate is fixed (fate map)
- cells become structurally and functionally specialised

Question 23

What is gastrulation?

Answer 23

process where a blastula is transformed into an embryo with body axes and 3 tissue layers
→ one of the most important stages in development

Question 24

What is the endoderm?

Answer 24

Inner layer - gastrointestinal tract, inc. liver, pancreas, and respiratory system

Question 25

What is the mesoderm?

Answer 25

middle layer - bone, muscle, heart, kidneys, bladder, ovaries/testes and inner layer of skin

Question 26

What is the ectoderm

Answer 26

outer layer of skin and nervous system

Question 27

In birds and reptiles, where does the epiblast originate from?

Answer 27

The blastodisc

Question 28

In mammals, , where does the epiblast originate from?

Answer 28

The inner cell mass

Question 29

In birds, what are the epiblast and they hypoblast?

Answer 29

Epiblast → embryo Hypoblast → extraembryonic membranes

Question 30

In mammals, what is the yolk replaced by?

Answer 30

A placenta

Question 31

What is organogenesis?

Answer 31

the formation of organs

Question 32

What is neurulation and when does it occur?

Answer 32

Early in organogenesis begins the formation of the nervous system in vertebrates

Question 33

Describe the 3 stages of neurulation

Answer 33

1. Thickening of the ectoderm = neural plate 2. Edges of neural plate thickens further, creates ridges 3. Ridges fuse over the top = cylinder (neural tube)

Question 34

Describe body segmentation

Answer 34

- Somites produce the vertebrae, ribs and muscles of the trunk and limbs - Neural crest cells produce peripheral nerves

Question 35

What are the 4 extraembryonic membranes in birds?

Answer 35

Yolk sac Amniotic sac Chorion Allantois

Question 36

What is the function of the yolk sac in bird eggs?

Answer 36

= nutrient transfer (through blood vessels)

Question 37

What is the function of the amniotic sac in bird eggs?

Answer 37

= surrounds embryo and secretes fluid = protection

Question 38

What is the function of the chorion in bird eggs?

Answer 38

= limits water loss & allows gas exchange

Question 39

What is the function of the allantois in bird eggs?

Answer 39

= Sac stores metabolic waste