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Spermatogenesis

Spermatogenesis

Spermatogenesis is the process by which haploid sperm cells are produced in the male testes. It starts with stem cells located close to the outer rim of seminiferous tubules. These spermatogonial stem cells divide asymmetrically to give rise to additional stem cells (meaning that these structures “self-renew”), as well as sperm progenitors, called spermatocytes. Importantly, this method of asymmetric mitotic division maintains a population of spermatogonial stem cells in the male reproductive...

Spermatogenesis

Spermatogenesis

Spermatogenesis is a complex process that involves the development of sperm cells from undifferentiated stem cells in the seminiferous tubules of the testes. The process is essential for the production of mature and functional sperm cells that are capable of fertilizing an egg.
The process of spermatogenesis can be divided into mitosis, meiosis, and spermiogenesis. During mitosis, the spermatogonia or stem cells divide to produce two identical daughter cells, type A and B spermatogonia. Type-A...

Sperm Structure and Semen Composition

Sperm Structure and Semen Composition

During ejaculation, males release around 2-5 milliliters of semen, which is a complex mixture of mature sperm and various fluids produced by accessory glands. The mature sperm cells measure approximately 60 micrometers in length and consist of a head, neck, midpiece, and tail. The head is flattened and tapered, measuring about 4 to 5 micrometers in length. It contains a nucleus with condensed chromosomes and an acrosome, a cap-like structure filled with enzymes essential for penetrating the...

Sperm Transport

Sperm Transport

The journey of sperm from its origin to the point of ejaculation begins within the seminiferous tubules of the testis. Here, Sertoli cells produce fluid that propels non-motile sperm through a series of conduits, starting with the straight tubules leading to the rete testis. This interconnected network of tubules acts as the initial pathway for sperm, guiding them into the efferent ductules and then into the epididymis for maturation.
The maturation phase occurs in the epididymis, where sperm...

Fertilization

Fertilization

During fertilization, an egg and sperm cell fuse to create a new diploid structure. In humans, the process occurs once the egg has been released from the ovary, and travels into the fallopian tubes. The process requires several key steps: 1) sperm present in the genital tract must locate the egg; 2) once there, sperm need to release enzymes to help them burrow through the protective zona pellucida of the egg; and 3) the membranes of a single sperm cell and egg must fuse, with the sperm...

Infertility in Males

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Male infertility affects millions of couples worldwide, arising from various factors that impact different stages of the reproductive process. An endocrine imbalance resulting from conditions like hypogonadism, Klinefelter syndrome, or pituitary disorders can disrupt hormone levels and reduce sperm production. Testicular defects, such as tumors, cryptorchidism, atrophic testes, abnormal sperm morphology, and low sperm count or motility, may arise due to genetic factors, structural...

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Related Experiment Video

Updated: Jul 13, 2026

Sperm Collection of Differential Quality Using Density Gradient Centrifugation

Sperm Collection of Differential Quality Using Density Gradient Centrifugation

Published on: November 29, 2018

Making sperm: design, quality control and sperm competition.

Tim R Birkhead¹, Simone Immler

¹Department of Animal & Plant Sciences, University of Sheffield, Sheffield, S I0 2TN, UK. T.R.Birkhead@sheffield.ac.uk

Society of Reproduction and Fertility Supplement

|July 25, 2007

Summary

Postcopulatory sexual selection significantly impacts sperm design, influencing sperm numbers and phenotypes. Reduced sperm competition leads to energy-saving adaptations in mammals and birds.

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Area of Science:

Evolutionary biology
Reproductive biology
Zoology

Background:

Spermatozoa exhibit remarkable diversity across taxa and individuals.
Fertilization mode, phylogeny, and postcopulatory sexual selection are key factors influencing sperm variation.
Postcopulatory sexual selection encompasses sperm competition and cryptic female choice.

Purpose of the Study:

To test the hypothesis that postcopulatory sexual selection shapes sperm design.
To investigate methods for measuring the intensity of postcopulatory sexual selection.
To understand how fertilization mode and phylogeny influence sperm design studies.

Main Methods:

Comparative analysis of sperm design across different taxa.
Examination of sperm characteristics in relation to sperm competition intensity.
Statistical control for fertilization mode and phylogenetic history.

Main Results:

Evidence linking postcopulatory sexual selection to inter-specific sperm differences is currently mixed.
Reduced sperm competition in mammals and birds correlates with decreased sperm numbers.
Lower sperm competition is associated with unusual sperm phenotypes, increased inter-male variability, and higher pleiomorphy within ejaculates.

Conclusions:

Postcopulatory sexual selection is a significant driver of sperm design evolution.
Observed sperm variations in mammals and birds under reduced competition may represent energy-saving adaptations.
Further research is needed to fully elucidate the complex interplay between sexual selection and sperm evolution.