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Sexual Reproduction Why Sexual Reproduction? (from a biological standpoint) • Asexual Reproduction – gives the same result over and over. – No mate is required. – Allows for no variation. • Sexual Reproduction – Another individual is required, usually of the opposite gender. – Gives different results every time – Provides for variation – Leads to better chance of survival for the species. Types of Sexual Reproduction • 1. External Fertilization – Egg is fertilized outside the females body – Ex. Fish, frogs, fungus, plants, worms, some insects. • 2. Internal Fertilization – Egg is fertilized inside the females body – Ex. Mammals, reptiles, birds, sharks, many insects Hermaphrodites – Organisms with both male and female sex organs External fertilization • Must occur in moist environment. • Large number of gametes released. (majority wasted or eaten) • Little to no parental care. Internal Fertilization • Less gametes needed. • Increased chance of fertilization. • Better protection for developing young. • Allows animals to survive outside water. Hermaphrodites • Can be internal or external, usually external. • Mates generally exchange gametes • Increases chance of finding viable partner. Males vs. • Testes – Male gonads (sex organs) – Produce sperm • Sperm – Males gametes (sex cells) – Are continually produced once puberty is reached. Females • Ovaries – Female gonads (sex organs) – Produce eggs. • Egg – Female gametes (sex cells) – Female born with limited number of eggs. Male Reproductive System External Structures Penis Delivers sperm to female reproductive tract. Scrotum Sac of skin contain a pair of testes Testes Olive size structures…which contain tightly coiled seminiferous tubules. Duct System Epididymus Store sperm for several months; where sperm mature Vas Deferens 45cm long(18”)…propels sperm to ejaculatory duct. Urethra 15cm (6”) Carries both urine & semen out of the male’s body. Male Reproductive System (con) Accessory Glands Seminal Vesicles Secrete fluids with nutrients which accounts for 60% of semen Prostate Gland Size of a chestnut…it encircles the urethra. Secretes fluid that contains nutrients & enzymes which activate sperm. Cowper’s Glands Secretes a mucus which neutralizes traces of acidic urine in the urethra. Semen Mixture of sperm & fluids that provide a transport medium, nutrients, & chemicals to help activate the sperm. Male Reproductive System Spermatogenesis • Sperm formation – Begins in puberty – Sperm are continually produced in the testes. – Stored in the epididymus until ejaculation. – Travels via vas deferens past 3 glands – Exits the penis through the urethra – Human sperm are not truly viable until inside the body of a human female. Anatomy of a sperm • Head – Contains the nuclear material = DNA – Covered by acrosome = enzyme for breaking down egg barrier • Midpiece – Full of mitochondria = Energy • Tail – Flagella for movement. Males Secondary Sex Characteristics Body Hair; pubic region, armpits, chest, face, etc… Muscle development Deepening up the voice Other interesting tidbits • Temperature – In humans and many animals, sperm require temp lower than body temperature. – This is why testes are found outside the body. • Ejaculated semen can reach the speed of 200” per second. • Sperm can survive in a females body for up to 3 days. • 25% of sperm are deformed from beginning. Female Reproductive System *Female is more complex than the male, because besides producing gametes, her body must prepare to nurture a developing embryo for about 9 months. Organ Structure and Function Ovaries Each ovary contains many follicles (one egg surrounded by follicle cells). Formed at birth. Produces estrogen. Puberty-one follicle matures & releases an egg during each menstrual cycle. Fallopian Tubes or Oviducts Do not touch the ovaries. Funnel like opening surrounded with cilia. Distil end connects to the uterus. Site of fertilization Female Reproductive System (con) Organ Structure and Function Uterus Thick muscular organ shaped like a pear. The lining is the endometrium, it is richly supplied with blood vessels. Cervix Neck of the uterus opens to the vagina. Vagina Thin walled chamber serves as repository for semen. Forms the birth canal. Vestibule Chamber-like area formed by 2 pairs of skin folds covering the vaginal and urethral openings. Clitoris Bulb of erectile tissue at the front edge of the vestibule. Bartholin's Gland Small gland located near opening of vagina. Secretes a mucus Female Reproductive System MAMMARY GLANDS *Found in both sexes…normally only function in females. Biological role is to produce milk for a newborn baby. This occurs after reproduction. (Modified sweat glands) Menstrual Cycle *Hand-out Average length 28-30 days (21-40 days) Ovulation—when a follicle of the ovary ruptures & releases an egg. Many Hormones play a role in Menstrual Cycle: LH—luteinizing hormone FSH—follicle-stimulating hormone GnRH—gonadotropin-releasing hormone Estrogen—female sex hormone Progesterone—works with estrogen OOGENESIS (EGG PRODUCTION) • Eggs are produced in follicles in the ovaries. – They are not yet fully formed. They complete this during each menstrual cycle. One at a time. – The rest are just waiting!! (Suspended in a metaphase state) • Egg numbers are limited in females and are not continually produced. – Birth = 1 million eggs. No more are produced. – Puberty = number is less than 400,000 – Less than 500 eggs are released from puberty to menopause. From Ovary to Uterus • Once a month, a single egg finishes production and is released by the ovary into the oviduct or fallopian tube. • If fertilization occurs, it occurs in the oviduct. • The fertilized egg (Zygote) implants into the uterus where it is nourished during pregnancy. • Menstrual cycle stops during pregnancy. It resumes after birth. If pregnancy does not occur... • If fertilization does not occur, the egg does not implant in the uterus. It may pass out of the females body, or be absorbed by the females body. • If implantation does not occur, the females body begins the process of menstruation, where the body builds a new uterine lining and discards the old one. • This is all controlled by hormones released from the egg itself. – (Many birth control pills work using these hormones) Pregnancy • Pregnancy is different for all species of animals. • Gestation Period – time from pregnancy until birth of offspring. – Dogs 51-80 days (7-12 weeks) – Monkeys 5 – 8 months – Humans - 9 months – Elephants - 2.5 years Types of Pregnancy • Oviparous – Embryo develops in egg outside the body • Fish, amphibians, many reptiles, birds • Ovoviviparous – Embryo develops in egg, but inside the body • Some snakes, most sharks. • Viviparous – Embryo develops inside the body connected to mother by a placenta (organ that nourishes the body) • Most mammals Human Pregnancy • Consists of 3 trimesters 1.Most critical period of development. All body systems develop 2. Very rapid growth of fetus. 3. Fetus triples its weight during the 3rd trimester. 3 trimesters Name of baby during Pregnancy • Zygote – when egg has become fertilized. • Embryo - 0-8 weeks. – (see picture) • Fetus - 8 weeks-birth. – The baby can now be identified as human. • Baby – after birth. (Joe, Suzy) Stages of labor • Labor – a series of Uterine contractions that force the baby out of the body through the vagina • 1. Dilation – Cervix dilates – Amnion breaks. • 2. Expulsion – Baby exits through vagina • 3. Afterbirth – Placenta and umbilical cord are forced out the vagina. Multiple births • Fraternal twins – Result of two eggs fertilized by different sperm. • Identical twins – Result of one egg splitting during development. • Siamese twins – Result of one egg not completely splitting during development Determination of sex • Girl – XX (51%) • Boy – XY (49%) • Turner’s Syndrome – XO (1/5000) • Klinefelters Syndrome – XXY (1/700)