1. Meiosis and Gamete Formation

2. Gametes Gametes =sex cellsGametes =sex cells Gametes form from germline cells via meiosisGametes form from germline cells via meiosis –Male gamete =sperm –Female gamete =oocyte (egg) A male and a female gamete come together to form a new individualA male and a female gamete come together to form a new individual –Somatic (non-gamete) cells have 46 chromosomes (diploid) –Gametes have 23 chromosomes (haploid) ½ + ½ = 1 whole½ + ½ = 1 whole

3. Human Karyotype

4. Remember… Figure 3.2 Homologous pair of chromosomes Homologous pair of replicated chromosomes Replicated chromosome (2 sister chromatids connected at centromere) A chromosome

5. Meiosis Produces gametes (1n or haploid) from somatic germline cells (2n or diploid)Produces gametes (1n or haploid) from somatic germline cells (2n or diploid) Figure 3.1 from motherfrom fatherchild meiosis reduces genetic content too much!

6. Meiosis Produces gametes (1n or haploid) from somatic germline cells (2n or diploid)Produces gametes (1n or haploid) from somatic germline cells (2n or diploid) Mixes up genetic informationMixes up genetic information –Diversity is important! Consists of 2 divisionsConsists of 2 divisions –Meiosis I –Meiosis II Figure 3.1 Haploid Diploid Meiosis I (reduction division) Meiosis II (equational division) Haploid Meiosis overview

7. Meiosis I Interphase (CHROMOSOMES REPLICATE)Interphase (CHROMOSOMES REPLICATE) Prophase IProphase I Metaphase IMetaphase I Anaphase IAnaphase I Telophase ITelophase I

8. Interphase Precedes Meiosis IPrecedes Meiosis I Cell grows and organelles are madeCell grows and organelles are made CHROMOSOMES ARE REPLICATEDCHROMOSOMES ARE REPLICATED Homologous pair of chromosomes Homologous pair of replicated chromosomes

9. Prophase I Pro =forward, forthPro =forward, forth Chromosomes condenseChromosomes condense Nuclear envelope breaks downNuclear envelope breaks down –Membrane surrounding the nucleus Centrioles move to opposite polesCentrioles move to opposite poles Spindle fibers growSpindle fibers grow Chromosomes synapse and crossing over occursChromosomes synapse and crossing over occurs Q4 Prophase

10. Crossing Over (Recombination) Replicated chromosomes pair up with their homologsReplicated chromosomes pair up with their homologs –i.e. chromosome from mom and chromosome from dad get together Genetic information is exchangedGenetic information is exchanged –Like shuffling a deck of cards and re-dealing Homologous pair of replicated chromosomes Synapsis New combinations of genetic info Q7

11. Metaphase I Meta =after, withMeta =after, with Homologous chromosome pairs line up at the midlineHomologous chromosome pairs line up at the midline –Line up is random so that INDEPENDENT ASSORTMENT takes place Spindle attaches to chromosomes at the centromereSpindle attaches to chromosomes at the centromere –The centromere is where the sister chromatids are attached chromatids are attached Q4 Metaphase

12. Independent Assortment Another way in which meiosis increases diversityAnother way in which meiosis increases diversity Chromosomes line up at the midline in a random wayChromosomes line up at the midline in a random way Q3

13. Anaphase I Ana =againstAna =against Homologous pairs splitHomologous pairs split Homologs are pulled to opposite poles by the shortening of spindle fibersHomologs are pulled to opposite poles by the shortening of spindle fibers Q4 Anaphase

14. Telophase I Telo =completion of a goalTelo =completion of a goal Spindle breaks downSpindle breaks down Nuclear envelope forms in each of the new cellsNuclear envelope forms in each of the new cells Q4 Telophase

15. Summary of Meiosis I Prophase I (early) (diploid) Prophase I (late) (diploid) Metaphase I (diploid) Anaphase I (diploid) Telophase I (diploid) INTERPHASE

16. Meiosis II Interphase –Chromosomes DO NOT replicate!Interphase –Chromosomes DO NOT replicate! Prophase IIProphase II Metaphase IIMetaphase II Anaphase IIAnaphase II Telophase IITelophase II

17. Prophase II Nuclear envelope breaks downNuclear envelope breaks down –Membrane surrounding the nucleus Centrioles move to opposite polesCentrioles move to opposite poles Spindle fibers growSpindle fibers grow Q4 PII

18. Metaphase II Chromosomes line up at the midlineChromosomes line up at the midline Spindle attaches to chromosomes at the centromereSpindle attaches to chromosomes at the centromere –The centromere is where the sister chromatids are attached chromatids are attached Q4 MII

19. Anaphase II Centromeres splitCentromeres split Sister chromatids are pulled to opposite poles by the shortening of spindle fibersSister chromatids are pulled to opposite poles by the shortening of spindle fibers Q4 AII

20. Telophase II Spindle breaks downSpindle breaks down Nuclear envelope forms in each of the new cellsNuclear envelope forms in each of the new cells Chromosomes decondenseChromosomes decondense Q4 TII

21. Summary of Meiosis II Q2 Entire Overview Prophase II (haploid) Metaphase II (haploid) Anaphase II (haploid) Telophase II (haploid) Four nonidentical haploid daughter cells

22. Homologous pair of replicated chromosomes Synapsis New combinations of genetic info Homologous chromosomes in germline cells Square Dance

23. Males and Females are Different! Girls have a “flower” and boys have a “noodle”

24. Male Reproductive System Gametes are made in the gonadsGametes are made in the gonads –Sperm are made in the testes –Sperm are made and stored outside of the body 200-600 million sperm200-600 million sperm arereleased with each arereleased with eachejaculation!!! Trillions of sperm areTrillions of sperm are made in a lifetime made in a lifetime bladder urethra testis vas deferens epididymis bulbourethral gland seminal vesicle prostate

25. Spermatogenesis Q1 Entire process starts at puberty

26. Female Reproductive System Gametes are made in the gonadsGametes are made in the gonads –Oocytes are made in the ovaries A girl is born with just one million oocytes per ovaryA girl is born with just one million oocytes per ovary Only 400 eggs will beOnly 400 eggs will be ovulated between ovulated between puberty and menopause puberty and menopause vagina cervix uterus ovary uterine tube

27. Oogenesis Before birth Arrested in Prophase I After puberty (each month) Arrested in Metaphase II Upon fertilization

28. Polar Bodies Three polar bodies are generated due to the developing egg hogging all of the cytoplasmThree polar bodies are generated due to the developing egg hogging all of the cytoplasm –Polar bodies usually degenerate –If fertilized by a sperm, a blighted ovum develops and results in miscarriage