BIO BIO

• Spermatozoa

  Sperm cells released into the vagina for new life to begin
• Fertilization


  1. Spermatozoa swim through the cervix

  2. Spermatozoa survive vaginal contractions

  3. Spermatozoa dissolve and break through the zona pellucida

  4. Sperm penetrates the egg

  5. Egg's shell changes to block other sperm
• Pronucleus


  The genetic material in the sperm cell spreads out and forms a new membrane, becoming the male pronucleus with 23 chromosomes
• Meiosis II


  The entry of the spermatozoa triggers the egg cell (oocyte) to undergo meiosis II and develop into the female pronucleus also with 23 chromosomes
• Zygote formation


  1. The male and female pronuclei membranes dissolve

  2. Their genetic material combines

  3. Becomes part of a single diploid nucleus containing a full set of 46 chromosomes
• Zygote


  The first stage in the development of a genetically unique organism
• Embryo development


  1. Zygote begins descent to uterus

  2. Undergoes multiple cell divisions (mitosis)

  3. Becomes a solid ball of cells (morula)

  4. Transforms into a hollow ball of cells (blastocyst)

  5. Blastocyst breaks out of shell and implants in uterine wall

  6. Develops into an embryo surrounded and protected by the amniotic sac