3Sexual Reproduction2 parents are required and can produce 1 or more offspring that are genetically different from either parentBenefits: 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…..
5Male Reproductive Structures and their Functions Testes (testis sing.)Site of male gamete formation= spermatogenesisProduces testosteroneScrotumHolds the testes outside the bodyEpidydimusWhere sperm is storedVas deferensSperm travels through hereSeminal VesicleCreates seminal fluid which adds nutrients to semenCowper’s GlandCreates alkaline fluid to counteract acidity in vaginaProstate GlandCreates secretions for semenUrethraSemen and urine travel through this to the outside
7Female Reproductive Structures and their Functions OvarySite of oogenesis and estrogen and progesterone productionOviducts=Fallopian TubesSite of egg fertilization, egg travels through to uterus if not fertilizedUterusZygote implants here, embryo grows via placentaCervixCreates mucin strands for sperm to travel up into uterusVaginaReceives sperm, birth canal for fetusClitorisSensory organ similar to glans penis
8Test Yourself….so to speak! Name that part! 731069245811. Testis 2. Cowper’s Gland 3.Vas Deferens 4. Urethra 5. Epididymus 6. Oviduct 7. Ovary 8. Vagina 9. Uterus Prostate Gland
9Meiosis- 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 materialMetaphase 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.
10Meiosis in Detail Prophase I Homologous chromosomes thicken and attach to each other in a chiasma (chiasmata- plural)Crossing Over occurs between homologsThe nuclear envelops disintegratesThe spindle fibers form from centrioles that move to the poles of the cell
11Meiosis in Detail (cont’d) Metaphase IHomologous chromosomes line up at the equator of the cellSpindle fibers attach to the chromosomes
12Meiosis in Detail (cont’d) Anaphase IHomologous chromosomes separate from each other and go to opposite poles of the cellSister chromatids do not separate
13Meiosis in Detail (cont’d) Telophase ISpindle fibers disappearNuclear envelope may reappearCytokinesis occurs to create 2 cells having half the number of chromosomes of the parent cell
14Meiosis 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
15Meiosis in Detail (cont’d) Metaphase IIChromosomes line up at the equator of the cell
16Meiosis in Detail (cont’d) Anaphase IIThe sister chromatids separate and move to opposite sides of the cell
17Meiosis in Detail (cont’d) Telophase IINuclear envelopes reform and the spindle fibers disappearChromosomes relax into fine threadsCytokinesis occursBOTTOM LINE:**4 different haploid cells have been formed!
18Meiosis = 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?
19Meiosis: 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
20Meiosis: 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
21Comparing Mitosis and Meiosis 1. begins with one cell2. creates 2 identical diploid cells3. has only 1 stage of division4. DNA replicates before mitosis begins5. Occurs in all body cells at some point of life6. Crossing over is a rare eventMeiosis1. begins with one cell2. creates 4 different haploid cells3. has 2 stages of division4. DNA replicates before meiosis begins5. Occurs only in sex cells6. Involves crossing over as a normal event
22Sexual vs Asexual Reproduction 1. Requires two parents2. Creates offspring that are different than the parents3. Process occurs by meiosis, fertilization and then birth4. Harmful pathogens cannot wipe out entire populations as there is a variety in genetic make-up5. Increases the organism’s chance of survival and evolution6. Usually occurs in organisms that are more complex7. Requires more energy and time in raising the offspringAsexual1. Requires only one parent2. Creates offspring that are identical to the parent3. 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 capacity6. Usually occurs in organisms that are less complex7. Requires less energy and time in raising the offspring
23When Meiosis goes wrong? What could possibly go wrong in meiosis?Often mistakes occur: Where?-in the first division, but can occur in the second division as well, usually in egg formation-
24Bibliography and Credits Audesirk et al. Biology Life on Earth. Sixth Edition. Prentice Hall