Q4 - Invertebrate Embryology

Question 1

How does cleavage in an insect egg after fertilisation differ from other species?

Answer 1

They don’t undergo complete cleavage of the cytoplasm, only the genetic material is duplicated

Question 2

What are energids in insect embryogenesis?

Answer 2

Nuclei of zygote surrounded in cytoplasm

Question 3

What is the blastoderm in insect embryogenesis and how is it formed?

Answer 3

The blastoderm is a single layer of cells surrounding the yolk and is made when energids migrate to the periplasm

Question 4

What is the name of the early germ band in insect embryogenesis?

Answer 4

Germ anlage

Question 5

What is the germ anlage in insect embryogenesis and how is it formed?

Answer 5

It is the early germ band that forms through a thickening of blastoderm cells (become columnar)

Question 6

How does the germ band form from the germ anlage in insect embryogenesis?

Answer 6

The germ anlage undergoes invagination and proliferation to become 2 layers of cells
Outer-layer - ectoderm
Inner-layer - mesoderm

Question 7

What are the main stages of germ band development in insect eggs?

Answer 7

Cleavage > energid migration > blastoderm formation > germ anlage formation > germ band formation

Question 8

Give an example of an insect that has long germ type embryos

Answer 8

Drosophila melanogaster

Question 9

Give an example of an insect that has short germ type embryos

Answer 9

Mealworm beetle (Tenebrio molitor)

Question 10

How are short and long germ type insect embryos characterised?

Answer 10

Based on how much of the blastoderm they develop from

Long - most of blastoderm
Short - small part near posterior pole

Question 11

What are the main differences between short and long germ type insect embryos?

Answer 11

Long - germ anlage gives rise to entire body plan with segments forming simultaneously

Short - only head and anterior thorax develop initially, with posterior abdomen developing later