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“Let’s Talk About Sex”-ual Reproduction Parts, their functions and Meiosis The Human Life Cycle: Why do we reproduce? http://www.biosci.uga.edu/almanac/bio_103/notes/apr_4.html Sexual Reproduction • 2 parents are required and can produce 1 or more offspring that are genetically different from either parent • Benefits: creates genetic variation in a population which allows for evolution and adaptation as well as being able to battle parasites, viruses and bacterial pathogens; some species find it an enjoyable past-time! It also ensures your genes are passed on, like leaving something of yourself behind when you are gone! • Drawbacks: requires more time and energy, produces smaller numbers of offspring generally, requires both parents be in the same place at the same time (must find a mate!) • How does it happen?? You must learn a bit about the human structures first….. Male Reproductive Organs Male Reproductive Structures and their Functions Structure Function Testes (testis sing.) Scrotum Epidydimus Vas deferens Seminal Vesicle Site of male gamete formation= spermatogenesis Produces testosterone Prostate Gland Urethra Creates secretions for semen Semen and urine travel through this to the outside Holds the testes outside the body Where sperm is stored Sperm travels through here Creates seminal fluid which adds nutrients to semen Cowper’s Gland Creates alkaline fluid to counteract acidity in vagina Female Reproductive Organs Female Reproductive Structures and their Functions Structure Function Ovary Site of oogenesis and estrogen and progesterone production Oviducts=Fallopian Site of egg fertilization, egg travels Tubes through to uterus if not fertilized Uterus Cervix Vagina Clitoris Zygote implants here, embryo grows via placenta Creates mucin strands for sperm to travel up into uterus Receives sperm, birth canal for fetus Sensory organ similar to glans penis Test Yourself….so to speak! Name that part! 7 3 10 6 9 2 4 5 1 8 1. Testis 2. Cowper’s Gland 3.Vas Deferens 4. Urethra 5. Epididymus 6. Oviduct 7. Ovary 8. Vagina 9. Uterus 10. Prostate Gland 1 4 5 8 2 10 9 6 3 7 Test Yourself….so to speak! Name that part! Meiosis- The Process of making Gametes • • • • • OVERVIEW: 1st Division is very important as it reduces the numbers of chromosomes by half . Prophase I has the homologous chromosomes (chromosomes that appear identical to one another because they carry the same genes, one comes from our mom, and the other comes from our dad.) crossing over to exchange material Metaphase I have the homologous pairs line up at the equator of the cell and in Anaphase I, the homologous chromosomes separate and thus reducing the chromosome number in each cell. 2nd Division of Meiosis is exactly like mitosis, except that 2 cells start off in prophase 2 and you end up with 4 daughter cells that are completely different from each other. Meiosis in Detail • Prophase I – Homologous chromosomes thicken and attach to each other in a chiasma (chiasmata- plural) – Crossing Over occurs between homologs – The nuclear envelops disintegrates – The spindle fibers form from centrioles that move to the poles of the cell Meiosis in Detail (cont’d) • Metaphase I - Homologous chromosomes line up at the equator of the cell - Spindle fibers attach to the chromosomes Meiosis in Detail (cont’d) • Anaphase I - Homologous chromosomes separate from each other and go to opposite poles of the cell - Sister chromatids do not separate Meiosis in Detail (cont’d) • Telophase I - Spindle fibers disappear - Nuclear envelope may reappear - Cytokinesis occurs to create 2 cells having half the number of chromosomes of the parent cell Meiosis in Detail (cont’d) • Meiosis II –Prophase II * Same as mitosis – nuclear envelop disintegrates * Spindle fibers form and attach to each chromatid and the centromere of the chromosome Meiosis in Detail (cont’d) • Metaphase II – Chromosomes line up at the equator of the cell Meiosis in Detail (cont’d) • Anaphase II - The sister chromatids separate and move to opposite sides of the cell Meiosis in Detail (cont’d) • Telophase II – Nuclear envelopes reform and the spindle fibers disappear – Chromosomes relax into fine threads – Cytokinesis occurs BOTTOM LINE: **4 different haploid cells have been formed! Meiosis = Genetic Variability? • This cell has 4 chromosomes = 2N and creates 4 different possible gametes. • What happens when there are 6 chromosomes? How many possible different gametes can arise? • Does it matter if there is crossing over, or not? Meiosis: Spermatogenesis –Making Sperm • Notice that the outcome of this meiosis shows no crossing over, only a shuffling of chromosomes and the maturation of sperm (crossing over occurs more often than not occurring at all) • There are 4 different cells that arise from meiosis – each having only ½ the original amount of DNA Meiosis: Oogenesis – Making Eggs • There are still 4 different cells created, however, only 1 of them is used for fertilization • * note: the first meiotic division starts at ovulation, while the second meiotic division is not complete until fertilization occurs! • ** females are born with a preset number of potential gametes prior to birth Comparing Mitosis and Meiosis • Mitosis • 1. begins with one cell • 2. creates 2 identical diploid cells • 3. has only 1 stage of division • 4. DNA replicates before mitosis begins • 5. Occurs in all body cells at some point of life • 6. Crossing over is a rare event • Meiosis • 1. begins with one cell • 2. creates 4 different haploid cells • 3. has 2 stages of division • 4. DNA replicates before meiosis begins • 5. Occurs only in sex cells • 6. Involves crossing over as a normal event Sexual vs Asexual Reproduction • Asexual • 1. Requires only one parent • 2. Creates offspring that are identical to the parent • 3. Process may be by mitosis, spore formation, budding etc. • 4. Harmful pathogens can wipe out entire colonies of organisms due to the same genetic make-up e.g bananas! • 5. May decrease the organism’s evolutionary capacity • 6. Usually occurs in organisms that are less complex • 7. Requires less energy and time in raising the offspring • Sexual • 1. Requires two parents • 2. Creates offspring that are different than the parents • 3. Process occurs by meiosis, fertilization and then birth • 4. Harmful pathogens cannot wipe out entire populations as there is a variety in genetic make-up • 5. Increases the organism’s chance of survival and evolution • 6. Usually occurs in organisms that are more complex • 7. Requires more energy and time in raising the offspring Bibliography and Credits • http://www.biosci.uga.edu/almanac/bio_103/notes/apr_4. html • Audesirk et al. Biology Life on Earth. Sixth Edition. Prentice Hall. 2002. • http://www.accessexcellence.org/RC/VL/GG/index.html • http://www.grad.ttuhsc.edu/courses/histo/notes/female.ht ml • http://www.biosci.uga.edu/almanac/bio_103/notes/apr_8. html • http://www4.ncsu.edu/unity/users/b/bnchorle/ww w/index.htm
