Lecture 3: Fertilisation

Question 1

fertilisation is the

Answer 1

union of sperm and ovum (diploid offspring)

Question 2

why isn’t fertilisation as simple as it sounds

Answer 2

• Sperm must make it to the ovum
• Gametes must recognize each other
• Sperm must penetrate ovum
• Haploid egg nucleus and sperm nucleus must fuse to form diploid zygote (syngamy)
• Ovum must block entry of additional sperm (polyspermy) to avoid polyploidy (>diploid)

Question 3

2 types of fertilisation:

Answer 3

internal & external

Question 4

external fertilisation:

Answer 4

fusion occurs outside either parent (aquatic organisms)

Question 5

internal fertilisation:

Answer 5

sperm can only move through liquid.

Question 6

internal fertilisation how do terrestrial animals overcome the need for liquid

Answer 6

Sperm inseminated in seminal fluid (and oviductal fluid in female reproductive tract)

Question 7

sperm penetration of the ovum requires penetration of the

Answer 7

egg coat (structure varies across species and includes extracellular egg material)

Question 8

Sperm penetration of the ovum- MAMMALS

Answer 8

• Sperm penetrate cumulus cell layer via hyperactive motility
• sperm undergoes acrosome reaction to penetrate zona pellucida (ZP)
• sperm and oocyte plasma membranes fuse (mediated by sperm-egg recognition/attachment proteins)
• sperm nucleus (and certain other sperm components) enter ovum
• membrane & ZP block to polyspermy rapidly initiated

Question 9

Sperm penetration of the ovum- SEA URCHIN

Answer 9

1) contact with jelly coat
2) acrosome reaction
3) growth of acrosomal process -acrosomal proteins bind to protein receptors on fertilisation envelope
4) fusion of the plasma membranes of the sperm and egg
5) entry of sperm to nucleus
6) cortical reaction

Question 10

Cortical reaction:

Answer 10

a process initiated during fertilization by the release of cortical granules from the egg, which prevents polyspermy, the fusion of multiple sperm with one egg

Question 11

how do sea urchins avoid inter-specific fertilisation?

Answer 11

Requires species-specific bindin protein on acrosomal process (detected by egg plasma membrane protein receptors) for fusion to occur

Question 12

Lysin:

Answer 12

abalone (marine gastropod mollusc) sperm protein that dissolves egg envelope = one of the fastest evolving metazoan proteins known

Question 13

clear evolutionary pattern because reproductive molecules have

Answer 13

rapid diversification. -particularly those involved in sperm-egg recognition

E.g. human egg coat protein ZP2 is in top 5% most divergent molecules between humans and rodents