Meiosis: The Cellular Basis of Sexual Reproduction ( 감수분열 : 유성생식의 세포적 기반 )

1. Meiosis: The Cellular Basis of Sexual Reproduction(감수분열: 유성생식의 세포적 기반) Chapter 11

2. 염색체는 감수분열 첫 번째 분열의 중기에 정렬된다. 감수분열은 난자와 정자 같은 배우체를 형성하는 시기이다.

3. 11.1 The Mechanisms of Meiosis • Meiosis is based on the interactions and distribution of homologous chromosome pairs • Meiosis produces four genetically different cells with half the parental chromosomes

4. Sexual Reproduction • Sexual reproduction(유성생식) produces offspring by union of male and female gametes (배우자)(sperm and egg) • Meiosis produces gametes with half chromosome number • Evolutionary advantage: Genetic shuffling of sex

5. Fertilization • Fertilization fuses nuclei of egg and sperm • Zygote (접합자) cell produced by fertilization • Restores parental chromosome number

6. Homologous Chromosome Pairs • Paternal chromosomes(부계염색체)from male parent, maternal chromosomes (모계염색체) from female parent • Homologous chromosome pairs • Alleles may be different within homologous pairs • Meiosis separates homologous pairs • Before meiosis, diploid (2n) • After meiosis, haploid(n)

7. 그림 11.1. 감수분열의 주기와 수정

8. Meiotic Cell Cycle • Mitosis (유사분열; 체세포분열) and meiosis (감수분열) compared • Both: Similar cell divisions, meiosis divides twice • Mitosis: Two identical daughter cells, diploid (이배체) • Meiosis: Four genetically different cells, haploid (반수체) • Premeiotic interphases (감수분열 전 간기) similar to mitotic interphase • Chromosomes copied into sister chromatids (자매염색분체)

9. Meiosis I • Meiosis I: First meiotic division • Recombination exchanges segments between homologues • Produces two haploid cells with chromatids attached

10. Meiosis II • Meiosis II: Second meiotic division • Sister chromatids separate into separate cells • Produces 4 recombined haploid cells

11. 그림 11.2. 두번의 감수분열에 의한 4개의 반수체 핵의 생산

12. Meiotic Cell Cycle (1) • Prophase I (전기 I) • Sister chromatids condense to chromosomes • Synapsis (접합) (pairing of homologs) • Tetrads (사분체) (Fully paired homologs) • Recombination(재조합)mixes alleles across tetrads • Prometaphase I (전중기 I) • Nuclear envelope (핵막) breaks down • Kinetochores (동원체에 있는 방추사부착점) attach to polar spindles (극 방추사)

13. 그림 11.3 -1. 감수분열

14. Meiotic Cell Cycle (2) • Metaphase I and Anaphase • Tetrads align on metaphase plate • Homologs segregate, move to poles (sister chromatids attached) • Nondisjunction(비분리) creates abnormal chromosome numbers • Telophase I and Interkinesis(분열간기) • No change in chromosomes • Spindle disassembles

15. 그림 11.3 -2

16. Meiotic Cell Cycle (3) • Prophase II, Prometaphase II, and Metaphase II • Chromosomes condense, spindles form • Nuclear envelope breaks, kinetochores form • Chromosomes align on metaphase plate(중기판) • Anaphase II and Telophase II • Spindles separate chromatids • Spindles disassemble • New nuclear envelopes form

17. 그림 11.3 -3

18. 그림 11.3 -4

19. 그림 11.4 -1. 감수분열과 유사분열의 주요 단계 비교

20. 그림 11.4 -2

21. 그림 11.4 -3

22. Sex Chromosomes in Meiosis • Sex chromosomes • Different in males and females • Human females XX, males XY • XX fully homologous, XY homologous in short region

23. Sex Chromosomes in Meiosis • Meiosis and sex chromosome inheritance • Gametes produced by females may receive either X chromosome • Gametes produce by males may receive either X or Y chromosome

24. 11.2 Mechanisms That Generate Variability (유전적 다양성) • Recombination depends on physical exchanges between homologous chromatids • Segregation of maternal and paternal chromosomes is random • Random joining of male and female gametes in fertilization adds additional variability

25. Recombination of Chromatids • Recombination (crossing over) • Key genetic shuffle of prophase I • Tetrads held together at synaptonemal complex (시냅시스 복합체) • Two of four chromatids exchange alleles • Chiasmata or crossovers are points of exchange

26. 그림 11.5. 유전자 재조합을 완수한 염색분체 사이의 교환 효과

27. 그림 11.6

28. Random Segregation • Random segregation • Key genetic shuffle of metaphase I • Each chromosome of a homologous pair may randomly end up at either spindle pole • Any combination of maternal and paternal chromosomes can be segregated to gametes • 2X number of possible combinations

29. 그림 11.7. 중기I에서 3쌍의 염색체가 무작위로 방추사에 연결된 가능한 결과들

30. Random Fertilization • Random chance of male and female gamete forming zygote • Meiosis allows randomness necessary for Mendelian laws of inheritance • Recombination, random segregation, and random fertilization are mechanisms of randomness

31. 11.3 The Time and Place of Meiosis in Organismal Life Cycles (감수분열 시기와 장소) • In animals, diploid phase dominant and meiosis followed directly by gamete formation • In most plants and fungi, generations alternate between haploid and diploid phases • In some fungi and other organisms, haploid phase dominant and diploid phase single cell

32. Animal Life Cycles • Diploid phase dominates animal life cycles • Meiosis followed directly by gamete formation • Haploid phase is reduced and short, no mitosis • In males, all four nuclei from meiosis form separate sperm cells • In females, only one nucleus becomes an egg

33. 그림 11.8. 진핵생물에서 감수분열 시기와 장소의 차이

34. Plants and Fungi Life Cycles • Alternation of generations • Alternate between haploid and diploid phase • Fertilization produces sporophytes (포자체) • Diploid individuals • Sporophytes produce haploid spores (meiosis) • Multicellular gametophytes (배우체) (mitosis) • Gametophytes produce gametes

35. Other Fungi and Algae Life Cycles • In some organisms, diploid phase limited to single cell zygote • Zygote (접합자) undergoes meiosis • Mitosis only occurs in haploid cells • Gametes usually designated + or -