Passing information on to the next generation…

» Compared to many animals and other organisms where fertilization occurs outside of the organism, in humans and other mammals, fertilization occurs inside, giving the parent more responsibility for the development of the offspring

» Development of sperm ˃Through MEIOSIS ˃Meiosis- One cell with full genetic code divides into 4 cells, each with half of the genetic code- each is one sperm ˃Since humans have 46 chromosomes, the chances of any two sperm having the same combination of 23 chromosomes is nearly 0, so no two sperm are alike. ˃Each cell going through meiosis results in 4 sperm

» Testes- structures in scrotum where development of sperm takes place. » Vas deferens- small tube carrying sperm from testes to urethra » Urethra- tube carrying urine and sperm out of male body » Penis- structure containing urethra, evolved to excrete waste and fertilize females

» Sperm travel from testes through vas deferens to urethra » Sperm is mixed with fluids while traveling ˃Resulting mixture is called semen

» Males- genetically XY » Y chromosome holds code for testosterone » Testosterone is a hormone that informs that body to develop male characteristics

» Development of egg » One cell goes through meiosis, but only results in ONE fully developed egg ˃Other three produced are called polar bodies, and are much smaller ˃*since egg is so much larger, majority of cytoplasm and nutrients are concentrated into egg, not polar bodies

» Ovaries- structures holding and developing female’s eggs » Fallopian Tubes- tubes connecting ovaries to uterus. » Uterus- Where development of egg occurs if fertilization is successful » Vagina- structure designed for removal of waste, unfertilized egg, and, if fertilization occurs, baby.

» Progesterone and Estrogen ˃In absence of testosterone, fetus develops as female ˃Two hormones work together to regulate cycling of female reproductive system » Menstrual Cycle ˃Approximately 28 days- development of one egg at a time. Each cycle, one egg is released during ovulation. Egg passes down fallopian tubes. ˃If fertilization, then zygote releases chemicals to stimulate body to stop cycle ˃If no fertilization, body continues cycle with menstruation, the removal of the egg and the removal of the uterine lining

» Ovulation- egg released from ovary into fallopian tube » Fertilization ˃Semen travel up uterus, following chemical signature of the egg. ONE sperm enters the egg, resulting in union of two 23-chromosome cells, making one 46-chromosome cell ˃Cell will go through mitosis (copying and division) trillions of times to result in a fully developed human

» Development ˃Fetus- developing human- held within the female’s uterus until it is ready to be released ˃Placenta- umbilical cord of baby ends in a bunch of blood vessels. Mother’s blood vessels wrap around BUT DO NOT MIX WITH baby’s blood vessels- nutrients and oxygen diffuse into baby, while waste from baby diffuses back into mother’s blood ˃Amniotic Sac- Developing baby held in a fluid-filled bag that pads the baby from any trauma

» Contractions- uterus is very strong MUSCLE- begins to contract, pushing fetus down through pelvis ˃Causes cervix to open, allowing baby to move from uterus into vagina, then out of body » Afterbirth- after baby, placenta must leave mother

» Vasectomy- in males, vas deferens is cut ˃Done through small cut in scrotum ˃Prevents sperm from reaching urethra » Tube tying- in females, fallopian tubes cut and tied off ˃MUCH more invasive procedure- recovery takes considerably longer

» IVF (in vitro fertilization) ˃Sperm from male mixed with eggs removed from female outside of body ˃Fertilized egg(s) are implanted into female’s uterus ˃In extremes, females can be given hormonal treatments to convince body to hold the implanted zygote(s) +Sometimes many are implanted +Example- OCTOMOM!