Fertilisation (wk 1)

Question 1

What are the two end results of fertilisation

Answer 1

Combining of genes derived from two parents

Reproduction= creation of a new organism

Question 2

Why do some animals have a jelly coat

Answer 2

Marine animals
Protective function
May also have diffusible chemicals involved in sperm recognition, attraction and activation

Question 3

List the 5 main steps in fertilisation

Answer 3

Chemoattraction
Acrosome reaction
Binding of the sperm to the egg envelope
Passage of the sperm through the extracellular envelope
Fusion of the egg and sperm membranes

Question 4

Compare and contrast the acrosome reaction in sea urchins and mice

Answer 4

Sea urchin:

• Egg jelly sends chemical cues
• Acrosomal process during acrosomal reaction digest through the egg jelly layer
• The acrosomal process is involved in binding to the vitelline envelope
• Acrosomal process fuses with egg membrane

Mice:

• Female reproductive tract activates the sperm
• Sperm binds to ZP
• Acrosomal reaction to digest ZP
• Sperm binds to egg membrane

Question 5

What is the primary interaction between the sperm and the egg?

Answer 5

Chemoattraction
Egg coat might have chemoattractants
Female reproductive tract has chemoattractants

Question 6

Explain how the sperm recognises the egg in sea urchin fertilisation

Answer 6

Jelly coat/egg secrete small soluble peptides to attract the sperm
Molecules bind to the sperm surface, activates the sperm, influx of calcium, sperm now has directional movement (following the gradient)

Question 7

What is the secondary interaction between the sperm and the egg?

Answer 7

Acrosomal reaction
In sea urchins: acrosomal process digests the egg jelly coat
acrosomal process is driven by polymerisaton of actin filaments

Question 8

Explain what happens in gamete fusion

Answer 8

Egg and sperm fuse
Calcium is released from stores which activates the egg, crucial metabolic pathways are activated
Genetic material fuse
Secondary polar body fuses

Question 9

How are species specific gamete recognition systems affected when fertilisation is internal?

Answer 9

Don’t need complex systems (species hybridisation is usually not an issue)

Question 10

Where do the sperm that aren’t competent get caught?

Answer 10

Cumulus oophorus cells

Question 11

Compare and contrast mammalian and sea urchin fertilisation

Answer 11

Refer to hand drawn flow chart

Question 12

Immediately after mammalian sperm and egg fuse what occurs

Answer 12

Activation of egg metabolism (increase in calcium ions)
Reinitiating of egg cell cycle, cell division and resumption of DNA and protein synthesis
Burst of oxygen reduction is seen= used to crosslink the fertilisation envelope

Question 13

When does the acrosome reaction occur in vivo?

Answer 13

Usually occurs after the sperm has binded to ZP

Most studies use eggs stripped of cumulus

Question 14

What happens when polyspermy occurs?

Answer 14

Embryonic cells with an uneven number of chromosomes

Too many centrosomes= two mitotic spindles form, this disrupts cleavage and chromosome inheritance= unviable embryo

Question 15

Distinguish between the fast and slow block

Answer 15

Fast= immediate change in resting potential of the egg membrane= repels excess sperm

Slow= cortical reaction, physical change in the membrane mediated by calcium ions

Question 16

Describe how sea urchins prevent poly spermy

Answer 16

Fast block: before fertilisation the egg cytoplasm has a high concentration of potassium and low concentration of sodium ions relative to the outside sea water, sodium ions then enter the egg and change the potential, additional sperm cannot bind to a positively charged membrane

Slow= cortical granules (in the cortex) fuse with egg cell membrane, proteins absorb water and expand the space inbetween the egg and vitelline envelope, causes it to rise and harden around the egg, physical barrier

Question 17

What are the three main tactics for mammalian prevention of polyspermy?

Answer 17

1. female reproductive tract is formidable
2. cumulus cell layer can trap sperm
3. bodies natural defence e.g. innate immunity