UNSW Embryology

Week 1

© Dr Mark Hill (2009)

Acknowledgements

Introduction

Gametes are formed in the male (see testis histology) and female (see ovary histology ) gonads, by the mechanism of meiotic cell division. The generation of gametes, and their regulation, is substantially different in males and females.

Female Gametogenesis

In females, the total number of eggs ever to be produced are present in the newborn female.

1. In females, all eggs are arrested at an early stage of the first meiotic division as a primary oocyte. Following purberty, during each menstrual cycle, pituitary gonadotrophin stimulates completion of meiosis 1 the day before ovulation.

See large image with labels

2. In meosis 1, a diploid cell becomes 2 haploid daughter cells. One cell becomes the secondary oocyte the other the first polar body.

See large image with labels

3. The secondary oocyte then undergoes meiosis 2 which arrests at metaphase and will not continue without fertilization.

Ovulation releases this oocyte from the ovary.

See large image with labels

Male Gametogenesis

In males, sperm continues to be generated throughout life from a stem cell population in the testis.

Sex Determination Summary

• Mammalian sex determination is regulated by chromosomes.
• Females have two X chromosomes. (XX)
• Males have a single X and a small Y. (XY)
• The X and Y chromosome are morphologically and functionally different from each other.
• Evolutionary studies have shown that the Y was once the homologous pair for X.
• It is only in the last 5 years that we have some idea about how these two types of chromosomes may be regulated and genes of inportance located upon them.
• In females the main scientific problem was that of gene dosage, only one copy of X chromosome is needed to be active.
• In males the main scientific problem was what on the Y chromosome determined "maleness", and how did it do it.

See Also: Male Sex Determination (sry) and Female X Inactivation (xist)

XY male genotype

Quick Links

Week 1 Pages:

Introduction | Abnormalities | Gamete formation | Cell division | Fertilization | Zygote | Blastocyst | Male sex determination| X inactivation | References | Text only page | WWW Links |

Development Notes ----------------- Menstrual Cycle Week 1 Week 2 Week 3 Week 4 Placenta Serial Images Genes/DNA Molecular Dev Abnormal Dev Postnatal Dev Notes Index

System Notes ----------------- Heart/Cardiovascular Respiratory Coelomic cavity Gastrointestinal Tract Head and Neck Neural Neural Crest Eye Ear Nose Endocrine Urogenital Musculoskeletal Integumentary

Movies ----------------- Embryo Growth Ultrasound Week 1 Week 2 Week 3 Week 4 Stage 13/14 Stage 22 Neural Head and Neck Heart Vasculature Gastrointestinal Urogenital Other Embryos Larsen Internet

Other Embryos ----------------- Chicken Fly Frog Mouse Rabbit Rat Worm Zebrafish Guinea Pig

UNSW Embryology ISBN: 978 0 7334 2609 4

UNSW CRICOS Provider Code No. 00098G