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The Reproductive System: Male and Female Sex Cells, Chromosomes, and Meiosis

Learn about the production of sex cells in males and females, the role of chromosomes, and the process of meiosis. Understand the structures and functions of the male and female reproductive systems.

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The Reproductive System: Male and Female Sex Cells, Chromosomes, and Meiosis

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  1. Chapter 3

  2. QSR #3 • 1. Give 2 names for the female sex cell. ________ and ____________. • 2. The production of sperm cells is called ______________ while the production of female eggs is called _______________. • 3. Both females and males have ________, • which provides the location for sperm and • egg development. In males it’s the • ________ and in females it’s the ________. • 4. This is what has to dilate 10 cm’s in order for a • baby to be born: ______________

  3. The reproductive system • The Male: • Sperm cells develop in the seminiferous tubules and are packed into the testes/testicles • Secretions from 3 glands (prostate gland which secretes a thin,milky material that activates sperm to swim, seminal vesicles which secrete sugar for energy, and the bulbourethral gland which secretes a mucus to coat the urethra) + sperm =seminal fluid • sperm exit through the vas deferens and out the urethra

  4. The Female: • Eggs (oocytes) develop in the ovaries (female gonads) • Inside each ovary, a newborn female has about a million oocytes • At puberty, one is released per month -- ovulation • They leave egg, enter the uterine tube, which carries it to the uterus • If fertilized, it implants into the uterus for 9 mths

  5. If the oocyte is NOT fertilized, it gets expelled during the monthly menstrual cycle • Cervix: a muscucular circle at lower end of the uterus • **has to dialate 10 cm in order for a baby to be delivered out of the birth canal

  6. Types of Chromosomes -- REVIEW • Homologous Chromosomes: 2 sets of chromosomes, 1 from mom, 1 from dad • are same length, same appearance • 2 sets of 23 chromosomes (23 from mom 23 from dad) • 46 total chromosomes in each cell

  7. Diploid vs Haploid • Body cells are diploid: each cell has 2 copies of each chromosome (2n) • One copy from mom and one copy from dad • Gametes are haploid: (n) only one copy of each chromosome • Sperm = 22 autosomes + 1 X or Y • Egg = 22 autosomes + 1 X

  8. Practice • What if an insect’s diploid number was 64, what would its haploid number be? • What is its haploid number was 8, what would its diploid number be???

  9. For HUMANS ONLY • Haploid • N=23 • Sex cells (gametes) • Diploid • 2N= 46 • Somatic cells (body cells)

  10. Chromosomes • Mosquito 6 • Drosphilia 8 • Housefly 12 • Garden pea 14 • Corn 20 • Sugarcane 80 • Adder’s tongue fern 1262 • +++++++++++++++++ • Frog 26 • Mouse 40 • Human 46 • Chimpanzee 48 • Orangutan 48 • Gorilla 48 • Horse 64 • Dog 78 • Duck 80 • ++++++++++++++++++

  11. Meiosis • Process by which reproductive organs( ovaries and testes) make your haploid sex cells –egg and sperm • “n” meaning haploid: • Only one copy of each chromosome • Mitosis forms diploid somatic cells (body cells)

  12. Meiosis • Produces haploid cells: • Supports Mendel’s theory that each parent donates one copy of the chromosomes

  13. Homologous chromosomes are divided in Meiosis I. Sister chromatids are not divided until Meiosis II.

  14. Sexual Reproduction • Male gametes---sperm, “N = 23” • Female gametes ----eggs, “N = 23” • Zygote--- “2N = 46” • Is a fertilized egg

  15. Sketch on board • ***Meiosis starts with a blank cell containing 92 chromosomes (46 chromosomes were replicated during S phase). After Meiosis I, 2 cells are produced…each now with 46 chromosomes. Following Meiosis II, 4 new cells are produced, each containing 23 chromosomes – HAPLOID!!!**

  16. Meiosis IIsame as Mitosis • Prophase II • Spindle fibers form • Nuclear envelopes dissolve • Nucleolus breaks down • Metaphase II • Spindle fibers move chromosomes to the equator

  17. Meiosis • Interphase I– • Gap 1: longest stage, normal functions • S: chromosomes replicate • Gap 2: gets ready for division • 1 cell • 92 chromosomes

  18. 1. Prophase I • A. Chromosomes coil up • B. Spindle fibers form • C. Tetrads form – pairing of homologous chromosomes **DOES NOT OCCUR IN MITOSIS D. -1 cell -92 chromosomes…Why 92?

  19. Metaphase I • A. Centromeres pull the tetrads to the middle of the cell • 1 cell • 92 chromosomes

  20. Anaphase I • A. Homologous chromosomes are pulled to opposite ends • B. Centromeres are not split!!!!!!! • 1 cell • 92 chromosomes

  21. Telophase I and Cytokinesis I • A. spindle broken down & chromosomes uncoil • B. cytoplasm divides & produces 2 new cells • C. Chromosomes are still doubled!!!!!!!!!!!!!!!!!!!! (unlike mitosis) • 2 cells • 46 chromosomes in each cell

  22. Meiosis II • A. Could possibly have a short Gap 1 • B. No replication – No S phase • C. No G2 • 2 cells • 46 chromosomes

  23. Prophase II(you can write same as Prophase I) • A. Spindle fibers form • B. they attach to centromeres • C. nuclear membrane disintegrates • 2 cells • 46 chromosomes

  24. Metaphase II • A. Chromosomes line up in the middle • 2 cells • 46 chromosomes

  25. Meiosis II • Anaphase II • A. Centromeres split • B. Chromatids now move to opposite poles • Telophase II • A. Chromosomes uncoil • B.Nuclear envelope forms & spindle fibers break down **2 Cells **46 chromosomes in each new cell

  26. At the end of Meiosis II • A. Again, like mitosis, is followed by cytokinesis (division of the cytoplasm) • B.Ending result is 4 new cells, each with 23 chromosomes • Males – 4 sperm cells • Females – 1 egg cell and 3 polar bodies (that will eventually degenerate) C. Sex cells are haploid. WHY?

  27. Meiosis IIsame as Mitosis • Prophase II • Spindle fibers form • Nuclear envelopes dissolve • Nucleolus breaks down • Metaphase II • Spindle fibers move chromosomes to the equator

  28. Meiosis • Provides for genetic variation which is important to species • Shuffles genetic information

  29. Prophase I • When “crossing over” can occur • Allows for genetic recombination– a new mixture of genetic material

  30. Meiosis • Sexual reproduction (humans): 1 sex cell (sperm or egg) has about 8 million chromosome combinations • Fertilization can lead to more than 70 trillion possible combinations

  31. Crossing Over/Recombination • Exchange of chromosome segments • Chiasma: point at which two different chromatids cross • Can occur many times within the same homologous chromosomes

  32. Draw the following:

  33. QSR #7 • 1. Explain 3 differences between mitosis and meiosis: • _______________________________________________ • _______________________________________________ • 2. In which stage do the tetrads form? __________ and explain the meaning of tetrad:_____________________ • 3. At the end of meiosis II, ____ daughter cells are produced with _____ chromosomes each. • 4. In the _____________ stage, centromeres do not actually separate, but they do in ______________. • 5. ___________over occurs in which stage?__________ • 6. _______________ and ______________ increase genetic variations, thus increasing the # of possibilities of what humans can look like.

  34. Prenatal Development • Ovulation: the release of an oocyte • Zygote: The fertilized egg • Embryo: a prenatal human • Fetus: from the start of the 9th week until birth

  35. Fertilization • Hundreds of millions of sperms are deposited into the vagina during intercourse • Sperm can survive inside a female’s body for 6 days – only 200 or more actually meet their goal ;) • BUT, the egg can only be fertilized 12-24 hours after ovulation

  36. Once the sperm reaches the egg: • Head of sperm releases enzymes that bore through a protective layer on the oocyte • Fertilization actually begins when the outer membranes of the sperm and oocyte meet • A wave of electricity spreads physical and and chemical changes across the surface of the oocyte – changes that keeps other sperm out!!!!

  37. Implantation • 1 day after fertilization, the zygote divides by MITOSIS – the resulting early cells are called BLASTOMERES. • Cleavage: early period of frequent cell division • Ball of cells hollows out • Center fills with fluid • Now have a blastocyst

  38. Implantation: A week after conception, the blastocyst implants into the lining of the uterus • This process takes about 1 week • The trophoblast (outer cells of the embryo) secrete HCG (human chorionic gonadotropin)– the pregnancy hormone • HCG prevents menstruation +++++++++++++++++++++++++++++++++++++++

  39. QSR #8 • 1. ______________ is the process of releasing an egg once a month from the ___________. • 2. The embryo becomes a fetus after the ____th week of pregnancy. • 3. Sperm can survive in the female body for _____ days. • 4. ____________ is the early period of rapid cell division. • 5. _____ is known as the “pregnancy” hormone since it stops ____________.

  40. Multiples • Twins are either fraternal or identical • Fraternal or dizygotic twins: occur when 2 sperm fertilize 2 oocytes • This can happen if ovulation occurs in 2 ovaries in the same month OR if 2 eggs leave the same ovary and both are fertilized • May run in the family IF the women tend to ovulate 2 oocytes a month

  41. IDENTICAL TWINS • Also called monozygotic twins • Form from a single fertilized egg – are genetically identical (same exact DNA) • Fig 3.16 Draw, explain, and UNDERSTAND!!!

  42. Simese Twins • 1 in 50,000 to 100,000 pregnancies • Results when an embryo divides into twins AFTER the point at which the 2 sets of cells can develop into 2 individuals • “Vanishing twin” syndrome: up to 70% of single births started out as twins

  43. Simese Twins

  44. Growth of the fetus • 4th week: rapid growth and differentiation • Arms and legs begin to extend from small buds • Blood cells form • Immature lungs and kidneys • 4-6 mm long • Sex is determined at conception

  45. 5th -8th week: • Head appears too large for its body • Apoptosis sculpts fingers and toes • Eyes are open..no lids • Size of a paperclip

  46. 12th week – 15th week: • Can see the sex via ultrasound • Fetus can suck thumb • Beginnings of teeth • Breathes amniotic fluid • Urinates and defecates into it • When 1st trimester ends

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