1- Fertilization is fundamental to sexual life cycles and is often seen as the start of...

1- Fertilization is fundamental to sexual life cycles and is often seen as the start of development.

Of the roughly quarter-billion sperm released in a typical primate ejaculate, only a few hundred have any significant chance of actually fertilizing an egg. It is also the case that all eggs are unlikely to be fertilized. In sea urchins, not all sperm will end up fertilizing an egg and not all eggs will be fertilized. Explain why this is the case in both systems by discussing what steps are required for gamete maturation and egg activation.

Expert Solution

Ans. Egg is produced in females during the ovulation period every month. Producing an egg is metabolically more costly than producing a sperm.So females produce one egg and males produce many sperms. In primates out of many billion cells produced only few are actually fertile and active and can travel the distance across many barriers and pH changes.Only sprem can fertilize the egg.Rheotaxis, thermotaixs and chemotaxis are known mechanisms in guiding sperm towards the egg during the final stage of sperm migration.The most thick layer is zona pellucida which surrounds the egg.In primates when the sperm binds to the egg the cortical reaction producing cortical granules which does not allow any more sperms to enter the egg.After the sperm binds to the egg there is acrosome reaction which gidest the hyaluronic acid in the oocytes.Thus fusion occurs.

In sea urchin the layer surrounding the egg is vitelline membrane.The acrosome reaction is first step in case of sea urchins after which fusion takes place.Then starts the cortical reaction.The cortical granules contain proteases that clip perivitelline tether proteins, peroxidases that harden the vitelline envelope, and glycosaminoglycans that attract water into the perivitelline space, causing it to expand and form the hyaline layer. The trigger for the cortical granules to exocytose is the release of calcium ions from cortical smooth endoplasmic reticulum in response to sperm binding to the egg.

gladiator answered 1 year ago

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