Contributing to Future Generations

1. Meiosis: Contributing to Future Generations

2. Where Do My Chromosomes Come From? • Every somatic cell (body cell) has 2 sets of chromosomes • 1 set from mom & 1 from dad • Any cell that has 2 complete sets of chromosomes = diploid or 2n

3. Each pair carries genetic information for the same trait • These chromosomes are said to be HOMOLOGOUS

4. Gametes – sex cells • When 2 cells come together during fertilization, each gamete (sperm or egg) can only have 1 set of chromosomes • Egg & sperm cells are said to be haploid (1n) = 1 set of chromosomes

5. Why is There a Need for Meiosis? Why do the ovary & testes cells go through meiosis? • Meiosis is the formation of SEX CELLS • Reduces the chromosome number in the cells (gametes) from 2 sets to 1 (diploid to haploid)

6. Diploid to haploid In humans: Parent 46 46 Parent Diploid (2N) Diploid (2N) Ovum 23 23 Sperm Haploid (N) Haploid (N) Zygote 46 Diploid (2N) c’some # cut in half fertilization

7. Chromosome Number Questions • If a horse retina cell has 36 chromosomes, how many does a horse sperm cell have? • If the n = 4 for fruit flies, how many chromosomes does a wing cell have?

8. A Homologous Pair is… • The 23 pairs of chromosomes in every body cell are also know as homologous pairs How do you know if 2 chromosomes are homologous? • 1 from mom, 1 from dad • Same banding pattern • Centromere is in the same position on both

9. The Chromosomes- Revisited

10. The Making of a Karyotype Photograph cell during metaphase Cut out chromosomes from the picture Arrange chromosomes in homologous pairs by comparing size, banding pattern, & centromere position Lay pairs out from largest to smallest with sex chromosomes at the end

11. What’s a Karyotype Used For? • Look for any abnormalities- either in structure or number (e.g. Down’s Syndrome) • Determine sex • Last pair = sex chromosomes • XX = female, XY = male

12. How Do We Get the Chromosomes for a Karyotype? • Need a cell • For an embryo- obtain cell through amniocentesis or chorionic villus sampling • For an adult- obtain any growing cell

13. Quiz Time • In Streptomycin fungus n = 11. What is the diploid number for this species? • If n = 16 for goldfish how many chromosome in a fin cell? • If 2n = 108 for black spruce trees then what is the haploid number?

14. The Results Products of Mitosis: 2 - 2n cells Diploid 2n 2n 2n Products of Meiosis: 4 - n cells n n n n 2n Haploid

15. Overview • Meiosis I – homologous chromosomes separate • Meiosis II – chromatid pairs separate

16. Meiosis: Reduction Division • Reducing the number of chromosomes

17. Where are we going?? • Males –4 sperm cells • Females – 1 ovum and 3 polar bodies

18. Meiosis I • 4 stages: • Prophase I • Metaphase I • Anaphase I • Telophase I

19. Prophase I 1. Sister Chromatids condense –c’somes 2. Nucleolusdisappears Homologouschromosomes pair up Spindle forms

20. Metaphase I Spindle fibers attachtocentromeres Homologous chromosomes line up in pairs tetrad

21. Anaphase I • Spindle fibers pull homologous chromosomes apart • Separates mom’s chromosomes from dad’s chromosomes • Sister chromatids stay together

22. Telophase I • Nuclear membranes form around the 2 new nuclei • Cell pinches into 2daughter cells

23. Summary of Meiosis I

24. Between Meiosis I and II there IS Interphase, but NO replication. Two cells from cytokinesis in Meiosis I are the same as the cells in Prophase II

25. Meiosis II • Meiosis II is like mitosis & consists of 4 stages: • Prophase II • Metaphase II • Anaphase II • Telophase II

26. Propahse II • Each cell has only mom’s or dad’s chromosomes with its copy (sister chromatid) • Nuclear membrane dissolves

27. Metaphase II • Sister chromatids line up across the metaphase plate

28. Anaphase II & Telophase II • Anaphase II • sister chromatids are pulled apart & migrate to opposite poles • Telophase II • Nuclear membranes reform

29. Summary of Meiosis II

30. The Final Product • Cytokinesis • The result is of meiosis is4 haploid gamete cells • Uneven cytokinesisin females • The result is 1 large egg cell & 3 non-functioning polar bodies

31. Ooogenesis • One ovarian cell divides into: • one viable egg cell • three polar bodies.

32. Spermatogenesis • Equal division of cytoplasm resulting in 4 equal size sperm

33. Comparison of Spermatogenesis & Oogenesis

34. Crossing Over • Crossing over (synapsis) occurs when genetic information is exchanged between the chromatids • Result = greater variability

35. Summary of Meiosis

36. Non-disjunction • Failure of chromosomes to separate properly during meiosis

37. Conditions Caused by Non-disjunction • Downs syndrome = Trisomy 21 - 3 copies of chromosomes 21  total of 47 chromosomes = 2n + 1 (chance of occurring in oogenesis increases with maternal age) • Turners syndrome = Monosomy X - has only one X chromosomes totalling only 45 chromosomes in her body cells = 2n-1 • Klinefelter’s syndrome = XXY- male which has an extra X chromosome = 2n + 1

38. Downs Syndrome • Trisomy 21 • Wide variety of problems • Developmental delays • Heart defects • Immune problems • Vision, hearing respiratory issues • Can also be very talented

39. Turner’s Syndrome • Monosomy X • Problems include • Short stature • Lack of ovarian development • Prone to kidney, cardiovascular, and thyroid problems • Difficulties with spatial orientation & awareness

40. Klinefelter’s Syndrome • XXYc= males • Problems include • Infertility • Language impairment • Less masculine body 3 Sex Chromosomes