GN 301 Module 2: Gametogenesis, Nondisjunction, Fertilization, and Early Development

Spermatogenesis

  • Occurs in the seminiferous tubes
  • How long to make mature sperm? 9-11 weeks
  • How many sperm per week? 1 billion
  • Define and describe importance in spermatogenesis:
    • ==Lumen:== The lumen is the hollow center of the tubule where formed sperm are released into the the duct system
    • ==Epididymis:== The epididymis is a coiled structure that receives immature sperm and stores it for several days

Spermatogonium 🡪 primary spermatocytes 🡪 secondary spermatocytes 🡪 spermatids 🡪 spermatozoa

Oogenesis

Females are born with about 1 million egg cells that are in the prophase I stage of meiosis

  • Polar Body

the small cell that is a byproduct of an oocyte meiotic division, which usually just disappears

  • Fertilization

the action of male sperm fertilizing a female egg to produce offspring

  • Syngamy

the fusion of two cells together in reproduction

Nondisjunction

==Errors in the separation of chromosomes== in meiosis. Occurs in Anaphase I or II when chromosomes move to opposite poles.

  • What are consequences of nondisjunction?

Gametes are produced with abnormal chromosome numbers. If these gametes are fertilized, individuals can be born with an ==abnormal number of chromosomes== which leads to genetic disorders.

Vocabulary

  • Zygote

A cell that has been fertilized by 2 gametes

  • Embryo

An unborn offspring in the process of developing, up to 8 weeks

  • Fetus

An developing offspring 8 weeks after conception

Characteristics of An Egg

An egg is the ==largest cell in the human body==. It’s spherical, doesn’t move on its own, and it is pushed by cilia into the Fallopian tubes after fertilization. Prior to birth, it is almost mature.

  • There are 500,000-750,000 potential eggs, but ==only 400-500 eggs are released for fertilization==, which can function for 10-15 hours after ovulation.

Characteristics of Sperm

A sperm is about 60 microns long and is ==motile==, swimming upstream to reach the egg to fertilize. There are 200 million sperm produced per ejaculation and males can make ==1 billion of them per week==. These sperm are capable of fertilizing eggs 48-72 hours after being produced.

Vocabulary: early development

  • Fallopian Tube (oviduct)

The tubes provide a passageway for a fertilized egg to make its way to the uterus.

  • Uterus

The uterus is where a fertilized egg is implanted during pregnancy, where a baby will develop until birth.

  • Cilia

The cilia help push the immobile fertilized egg into the Fallopian tubes after fertilization.

Fertilization and Early Development

  • How many sperm are ejaculated? 200 million
  • How many sperm reach the egg? around 50
  • How many sperm fertilize the egg? only 1
  • What are the layers that the sperm must penetrate in order to fertilize? (3 layers)

==Corona radiata, Zona pellucida, and the cell membrane==

  • What is fertilization and where does it occur?

==Fertilization== is when male sperm penetrates a female egg, which join together. It occurs in the Fallopian tubes.

  • What is syngamy and where does it occur?

==Syngamy== is where the nuclei of the egg and the sperm fuse to form a zygote (4-5 hr after fertilization). It also occurs in the Fallopian tubes.

  • What is implantation and where does it occur?

==Implantation== is the stage where the embryo attaches to the uterus and forms the placenta. \n

  • Define and Describe how these are produced (fetus, mother or both)

==Amnion==: the inner membrane surrounding embryo, created by the fetus

==Chorion==: outer membrane surrounding embryo, created by both the fetus and the mother

==Placenta==: an organ in the uterus that nourishes the embryo, develops 2 weeks after fertilization, created by both the fetus and the mother

==hCG (and what is it used for?)==: hCg is Human Chorionic Gonadotrophin, which is a hormone produced during pregnancy that helps support an embryo and stops menstruation