Animal development 2

Question 1

What is the animal pole in embryos?

Answer 1

Smaller, rapidly-dividing, non-yolky cells

Question 2

What is the vegetal pole in embryos?

Answer 2

Larger, slower-dividing cells with dense yolk granules

Question 3

Describe the reorganisation of the cell cytoplasm

Answer 3

Egg cytoplasm often reorganises after fertilisation
Before fertilisation, the egg is radially symmetrical
After fertilisation, the cytoplasm streams towards the vegetal pole, then back towards the animal pole but displaced to one side
This creates a bilateral symmetry and gives rise to a left and right side of the embryo

Question 4

Explain what Conklin (1902) found out about yellow cytoplasm

Answer 4

Cytoplasmic movement after fertilisation concentrates yellow cytoplasm at the vegetal pole
Only these yellow cells form muscles
This supports mosaic development
Yellow cytoplasm contains mRNA for a transcription factor called Macho1 associated with switching on genes associated with muscle cell development

Question 5

How do deuterostome cells perform cleavage?

Answer 5

Radial cleavage

Question 6

How do protostome cells perform cleavage?

Answer 6

Spiral cleavage

Question 7

How do insect cells perform cleavage?

Answer 7

Superficial cleavage

Question 8

What is a cell lineage fate map?

Answer 8

Fate map shows which cells develop into which tissues

The cell lineage is always the same in every individual

Question 9

Describe the movement of P granules in the cytoplasm

Answer 9

Inside P cells
After fertilisation, they become concentrated in the posterior of the embryo
By the 26 cell stage, they are only in the P4 cells which gives rise to germ cells
This supports mosaic development