Biol 240 Dr John Waters 413 Mueller Laboratory Reproduction Sexual Meiosis produces Spermatogenesis Human gametogenesis Oogenesis gametes egg cells and sperm cells Gametes are haploid n Sperm cell fertilizes Egg cell zygote diploid n 2n Figure 46 UN01 Primary spermatocyte n Secondary spermatocytes 2n n Primary oocyte n Polar body Secondary oocyte n n n n n n n Spermatids Sperm n Polar body n Fertilized egg Why reproduce sexually other than the obvious reasons Increased the total number of offspring over generations Increased number of offspring that survive over generations Which method preserves the genes in a population Which recombines the genes in a population produces new genes too So then Which is preferred when environment is stable and the organism is well suited to that environment What if the environment is unstable Reshuffling genes may also help remove the harmful genes The vast majority of eukaryotes reproduce sexually Reproduction Asexual Fission Sexual Meiosis produces gametes egg cells and sperm cells Gametes are haploid Sperm cell fertilizes Egg cell zygote diploid Parent splits into two individuals Pictured sea anemones Fragmentation Regeneration Body broken into pieces Regeneration of missing body parts on each piece Pictured flat worms Budding New individuals arise from outgrowths on existing ones Pictured hydra Parthenogenesis An egg develops like in sexual reproduction but an individual develops without fertilization Offspring are haploid or can be diploid too Pictured whiptail lizards No matter how you reproduce sexually or asexually reproduction is tied to environmental cues The environment day length temperature rainfall lunar cycles behavior of other individuals food supply anything really Affects hormone levels in the individual And those hormones bind to receptors in the individual s cells And the individual s biology and behavior are affected Examples Ewes ovulate in fall early winter so lambs are born in the spring when food is plentiful Daphnia reproduce either asexually or sexually depending on environmental conditions Parthenogenetic lizards they are ALL females reproduce more successfully if the females engage in sexual behavior No matter how you reproduce sexually or asexually reproduction is tied to environmental cues Other strategies among sexually reproducing organisms Hermaphroditism Each individual can produce both male and female gametes sperm cells and egg cells Everybody can hook up with everybody And in some cases individuals can self fertilize Sex reversal Under the right environmental cues an individual can change from one gender to the other i e boys change into girls or girls change into boys Fertilization Strategies there is more than one way to make a zygote Internal Fertilization male deposits sperm in or near External Fertilization female reproductive tract fertilization takes place inside female protects embryos from harsh environments requires cooperation between male and female mate choice courting female releases egg into environment then male fertilizes almost always requires a moist environment synchronous spawning chemical cues environmental cues asynchronous courting mate choice Pheromones Chemical messengers released into the environment that affect behavior physiology of other organisms Fertilization Strategies there is more than one way to make a zygote Internal Fertilization Parents produce fewer gametes sperm and egg but a higher percentage of zygotes fertilized eggs survive Protected against water loss and physical damage Several membranes When eggs laid usually have tough shell Placentas Mammary glands External Fertilization MANY more gametes produced but fewer zygotes survive Exposed to environment eggs usually covered by gelatinous mass Human Reproductive System Males don t trust everything you ve seen on the Internet Let s start where the gametes start Sperm cells are first formed via meiosis in the testes which are the gonads in males more details later The testes are held inside the scrotum As the sperm cells mature they are transported to the epididymis During ejaculation sperm cells Travel through the vas deferens Pass near the seminal vesicle And into the ejaculatory duct and then the urethra Along the way they mix with other secretions to form the semen Human Reproductive System Males don t trust everything you ve seen on the Internet Semen Sperm cells from testis mixed in a salt water solution 10 of volume Secretions from Seminal Vesicle 60 of volume thick yellow and alkaline contains carbs prostaglandins and proteins needed to coagulate semen Prostate Gland 30 of volume thin milky and contains buffers ions carbs and enzymes that cause semen to coagulate and then later to become thin and runny Bulbourethral Gland 1 of volume clear alkaline mucus Human Reproductive System Males don t trust everything you ve seen on the Internet During sexual arousal bulbourethral gland secretes its fluid to neutralize any acidic urine in the urethra penis becomes erect due to blood filling the spongy erectile tissue that makes up the shaft vasocongestion During orgasm and ejaculation all the components of the semen are pushed into the urethra emission and out of the tip of the penis expulsion by rhythmic smooth muscle contractions During resolution the body returns to normal Males then enter a refractory period lasting minutes to hours Human Reproductive System Males don t trust everything you ve seen on the Internet A little more about penises so to speak Anatomy shaft glans head prepuce foreskin average sizes Flaccid 3 4 inches long an inch or so in diameter Erect 5 7 inches long Around 1 5 inches in diameter Fun Fact Rodents raccoons walruses and whales all have a baculum a k a penis bone Human Reproductive System Females don t trust everything you ve seen on the Internet Let s start where the gametes start Egg cells oocytes are first formed via meiosis in the ovaries which are the gonads in females more details later The ovaries are inside the abdominal cavity Ovulation is when an egg cell surrounded by some support cells is pushed out of the ovary The egg cell is drawn into the oviduct and transported toward the uterus If fertilization occurs it will happen inside the oviduct and a zygote will be formed The zygote or unfertilized egg cell if no sperm were present is transported to the uterus Human Reproductive System Females don t trust everything you ve seen on the Internet The uterus Endometrium inner lining of