gametogenesis. fertlisation. embryoni development

Where does gametogenesis occur?

In gonads

Ovaries - females

Testes - males

Define

• spermatognia

• Primary spermatocytes

• Secondary spermatocytes

• Spermatids

• undifferentiated cells in testes

• Results from the first division of spermatogonia

• Formed by the first meiotic division of primary spermatocytes

• Formed by the second meiotic division of secondary spermatocytes

What is external fertilisation typical for?

Amphibians

In ovulated human oocytes, meiosis is arrested at

Metaphase II

Define

• oogonia

• Primary oocytes

• Secondary oocytes

• Ovum

• undifferentiated cells in ovaries

• Result from the division of oogonia

• Formed by the first meiotic division of primary oocytes but are arrested in metaphase II until fertilisation

• Fertilised egg

Describe the process of oogeneis

Two meiotic divisions

Uneven cytokinesis - one large egg and smaller polar bodies

Primary oocytes undergo meiosis I before birth, but meiosis II is completed only if fertilisation occurs

How many sperm are produced from each spermatogonium?

4

Describe the steps of fertilisation

• sperm recognises and binds to the zona pellucida - a protective layer around the egg

• The acrosome (structure on sperm) releases enzymes to penetrate zona

• Sperm penetrated and fuses with egg cell membrane

• Fusion of sperm and egg triggers completion of meiosis II in egg

• Mature egg and second polar body formed

What happens during cleavage in embryonic development?

Rapid mitosis of the zygote forms a solid ball of cells called the morula, which develops into a fluid filled blastocyst.

What is a blastocyst?

Fluid filled structure with an outer layer of cells and inner cell mass. It hatches from the zona pellucida and attaches to the uterus

What happens during implantation?

The blastocyst embeds in the uterine lining for nutrient exchange and trophoblast cells (the cell on the outside of the blastocyst) contribute to the placenta

What happens during gastrulation?

Three germ layers form - ectoderm, mesoderm and endoderm

Which develops into tissues and organs

What happens during neurulation?

Ectoderm forms neural plate

Which folds into neurual tube and ends up making up CNS

Difference between apoptosis and necrosis

Apoptosis - programmed cell death

Necrosis - uncontrolled cell death