BIOL 118 1st Edition Lecture 31 Outline of Last Lecture I Introduction to Chemical Signals in Animal II Cell to Cell Signaling An Overview III 3 Hormone Signaling Pathways IV Chemical Characteristics of Hormones V How is the Production of Hormones Regulated VI The Hypothalamus Pituitary Axis Outline of Current Lecture I Introduction to Animal Reproduction II Asexual Sexual Reproduction III Mechanisms of Sexual Reproduction Gametogenesis IV Fertilization Egg Development V Role of Sex Hormones in Sexual Reproduction VI Pregnancy Birth In Mammals Current Lecture Introduction to Animal Reproduction Reproductive systems of animals are highly variable o Some species switch between asexual and sexual reproduction o In sexual reproduction fertilization may be external or internal o Egg development may take place inside or outside the mother s body In humans the male reproductive system includes structures specialized producing storing sperm synthesizing semen Human female reproductive system includes specialized structures for producing eggs receiving sperm caring for the developing embryo o Hormones from the pituitary gland female reproductive organs regulate the menstrual cycle via positive or negative feedback o Pregnancy is maintained by hormonal signals from the embryo the mother s reproductive organs Asexual Sexual Reproduction Asexual reproduction based on mitosis results in offspring that are genetically identical to one another to their parent equivalent to cloning These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o Budding offspring forms in or on the parent when fully developed the offspring breaks away o Fission an individual splits into 2 organisms o Parthenogenesis female produces and offspring without fertilization from a male o Eggs can be produced by mitosis or meiosis Sexual reproduction based on meiosis fusion of haploid gametes usually from different parents results in offspring that are genetically different Mechanisms of Sexual Reproduction Gametogenesis Gametogenesis Mitotic cell divisions meiotic cell division developmental events that result in the production of male female gametes o Spermatogenesis formation of sperm Spermatogonia diploid cells that divide by mitosis to generate cells that undergo meiosis Occurs continuously through male s adult life Spermatogonia divide by mitosis to produce primary spermatocytes which undergo meiosis I produce 2 secondary spermatocytes At end of meiosis II result is 4 haploid cells called spermatids which mature into sperm o Oogenesis formation of eggs Oogonia diploid cells that divide by mitosis to form primary oocytes Only one of the 4 haploid product ovum matures into an egg Polar bodies other cells that do not mature into eggs Production of primary oocytes stops early in development or before birth o Vast majority occurs in a sex organ gonad Male testes females ovaries Four components of mammalian sperm o Head contains the nucleus enzyme acrosome for penetrating the egg o Neck contains 1 centriole which will combine with the centriole contributed by the egg o Midpiece contains mitochondria which supplies the ATP that sperm uses to swim to the egg o Tail with flagellum for swimming Contents of an egg cell o Yolk nutrient source loaded with protein fats o Vitelline envelope outside the cell membrane In sea animals may be surrounded by jelly like layer to protect the egg zonapellucida Fertilization Egg Development Fertilization joining of sperm egg to form diploid zygote o Many animal species release gametes into the environment external fertilization occurs Most of these lice in aquatic environments tend to produce large numbers of gametes Gametogenesis responds to environmental cues that indicate a favorable season for breeding Pheromones chemical messengers that might be involved in coordination of the release of the gametes o In other animals males deposit sperm into the reproductive tracts of females internal fertilization occurs Copulation males deposit sperm directly into the female reproductive tract with the aid of a copulatory organ penis Males may also package their sperm into a spermatophore which is then placed into the female s reproductive tract by the male or female Sperm competition competition between sperm from different males to fertilize the eggs of the same female o Second male advantage when two males mate with a single female the last one to copulate fathers 85 of the offspring produced not universal but widespread o In fruit flies second male s sperm physically dislodged replaced first male s gametes from female s sperm storage area Fluid that accompanies sperm is able to displace stored sperm from competing males Once fertilization occurs embryo is either laid as an egg outside the mother s body or retained inside o Oviparous egg is laid outside the mother s body the embryo develops in the external environment care of young varies Care of young is variable o Viviparous egg remains within the mother s body Embryo develops receives nutrition directly from the mother o Ovoviviparious offspring develops inside the mother s body but are nourished by nutrient rich yolk in the egg Anatomy of human male reproductive organs o Spermatogenesis sperm storage sperm are produced in the testes stored in the nearby epididymis o Production of additional fluids accessory are formed in the seminal vesicles prostate gland bulbourethral gland These accessory fluids are added to sperm before ejaculation or expulsion from the body o Semen combination of sperm accessory fluids expelled during ejaculation o Vas deferens tubes that transport sperm from the epididymis to the ejaculatory duct o Urethra longer tube that passes through the penis services both the reproductive urinary systems in males Female reproductive systems o Ovary where meiosis occurs egg cells ova are produced o Mature egg cell is a membrane bound structure consisting of a haploid nucleus a full complement of other organelles a large supply of nutrients in the form of yolk o Humans are viviparous vertebrates female retains the embryo provides the nourishment o External anatomy of human female reproductive system Labia minora majora folds of skin that cover the urethral vaginal openings Vagina chamber where semen is deposited during sexual intercourse through which a baby is delivered during childbirth Clitoris sensitive organ that develops from the same
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