Male Physiology and Genetics

Male Physiology Overview

• Male physiology is generally straightforward compared to the female reproductive system.

• Today's material is considered easier with fewer details to memorize.

Class Logistics

• Only one class remains after today, scheduled for next Tuesday.

• There will be a recitation next Thursday, as there's no regular class then.

Warm-up Questions: Hormone Graph Analysis

• The warm-up activity focuses on hormone graphs, similar to exam questions.

• Estrogen's Positive Feedback:

  • A spike in estrogen causes an increase in GnRH (Gonadotropin-Releasing Hormone).

  • This leads to a large spike in luteinizing hormone (LH).

  • The LH spike is responsible for ovulation.

• Progesterone Levels:

  • Progesterone levels are highest towards the end of the cycle but decrease right before menstruation.

• Menstrual Cycle Day One:

  • Day one is always the first day of menstruation.

  • Menstruation typically lasts from day one through day five of the cycle.

• Progesterone and GnRH:

  • Progesterone does not have a positive feedback effect on GnRH at point C because there's no progesterone yet.

• Class performance improved significantly compared to the last quiz.

Gametogenesis and Cell Division

Mitosis

• Mitosis is how somatic cells divide.

• Process:

  • A cell with 23 pairs of chromosomes duplicates its DNA.

  • It also doubles organelles, like mitochondria, and grows in size.

  • The cell then divides into two identical daughter cells.

  • Phases: Prophase, Metaphase, Anaphase, Telophase

• Cell Types:

  • Mitosis occurs in all body cells except sex cells and cells that do not divide.

  • Examples of cells that don't divide: red blood cells, heart cells, most brain cells

• Situations Requiring Mitosis:

  • Growth during puberty.

  • Recovery from injuries.

  • Regular cell maintenance.

Meiosis

• Meiosis is a different type of cell division used to produce sex cells.

• Process:

  • A cell with the normal amount of DNA doubles its DNA.

  • The cell divides, and then divides again, skipping DNA duplication in the second division.

  • The end result is four cells, each with half the amount of DNA.

  • These cells are suitable for sex cells (egg and sperm).

• Differences between Mitosis and Meiosis:

  • Meiosis results in four cells, while mitosis results in two.

  • Meiosis involves shuffling of chromosomes, resulting in non-identical cells.

  • Mitosis results in identical cells.

Twins

• Fraternal Twins:

  • Mom ovulates twice, releasing two eggs that are fertilized by different sperm.

  • Fraternal twins do not have the same DNA makeup and can be different sexes.

  • There can be a genetic tendency to ovulate more than one egg at a time.

• Identical Twins:

  • A single fertilized egg splits into two separate embryos during early development.

  • Identical twins have the same DNA because they originated from one egg.

Spermatogenesis vs. Oogenesis

• Spermatogenesis:

  • Stem cells divide through various stages to produce sperm cells.

  • The resulting sperm cells are all the same size.

• Oogenesis:

  • Divisions are unequal, resulting in one large cell (oocyte) and smaller cells called polar bodies.

  • Polar bodies do not develop further and are essentially discarded.

  • Oogenesis produces only one viable egg cell, which is much larger than sperm cells.

  • Polar bodies have a similar amount of DNA but lack organelles.

Visualizing Mitosis and the Genome

• Analogy of DNA as Yarn:

  • Normal cells have unwound DNA for reading instructions (genes).

  • During cell division, DNA is packed into thread-like structures (chromosomes).

  • Length of DNA in one cell: approximately three feet.

  • Skin cells example: Rubbing a finger on a table removes about 50,000 cells, leaving DNA equivalent to the distance from here to Orlando, Florida.

• Packing DNA:

  • DNA is coiled around proteins called histones.

  • Coils fold back on themselves, creating a tighter coil.

  • This process repeats multiple times, resulting in a visible chromosome under a microscope.

• Cell Division Speed:

  • The body makes about 3,000,000 red blood cells per second.

  • This process requires millions of cell divisions per second.

Anatomy of a Sperm Cell

• Tail: Propulsion system for swimming.

  • Sperm swim randomly but are guided by chemicals in the ejaculate.

  • These chemicals reverse peristalsis in the female reproductive tract, helping sperm move deeper.

  • They remain alive for about three days in the female reproductive tract.

  • The ejaculate's alkaline pH helps to balance out the vagina's more acidic environment.

• Midpiece: Contains a molecular motor and mitochondria.

  • Mitochondria provide energy (ATP) for swimming.

• Head: Contains the nucleus with half the DNA and an acrosome.

  • Acrosome: A vesicle containing enzymes that help the sperm penetrate the egg.

Fertilization

• Sperm reaches the egg, and receptors on the sperm recognize the egg's surface.

• Enzymes from the acrosome digest the protective layer (zona pellucida) around the egg.

• The plasma membranes of the sperm and egg fuse.

• Only the sperm's nucleus enters the egg's cytoplasm.

• Mitochondrial DNA:

  • All mitochondria in the fertilized egg come from the mother.

  • Therefore, everyone inherits their mitochondrial DNA from their mother.

• The egg seals off to prevent additional sperm from entering after the first sperm's nucleus enters.

• A genome is all of the DNA inside of a cell.

The Human Genome: Amazing Facts

• Size:

  • The human genome contains approximately 3.2 billion nucleotides (DNA letters).

  • Visualizing this amount: Equivalent to the letters in multiple copies of the entire Harry Potter series, Twilight series, Hunger Games, Chronicles of Narnia, Lord of the Rings, and Game of Thrones multiplied by six and doubled twice.

• Number of Genes:

  • The estimated number of genes in the human genome is about 20,000.

• Every cell contains full instructions:

  • Every cell in the body has the same set of instructions (DNA), but different cells express different genes.

  • Analogy: The genome is like a piano keyboard. By playing different keys (genes) in different patterns, various outcomes (cell types) are produced.

  • Physiology is like a symphony created by all of the cells playing the instrument of your genome differently, making different cells.

• Mitochondrial DNA:

  • Mitochondria have their own DNA, separate from the nuclear chromosomes.

  • Mitochondria are inherited exclusively from the mother.

  • Mitochondrial DNA does not undergo recombination, providing a record of the maternal line.

  • Molecular biologists reconstructs a map that shows our human migration out of Africa.

  • Every single human being alive today all descended from one single woman who lived in modern day Ethiopia Seventy Thousand Years ago. We call her mitochondrial Eve. Right?