1. Chapter 13 – Campbell’s 6th Edition
Meiosis and Sexual Life Cycles

2. Definitions Heredity:
transmission of traits from generation to the next
Variation:
slight differences in appearance
Genetics:
scientific study of heredity and hereditary variation

3. Genes
Genes:
coded information in the form of hereditary units (lots of genes on each chromosome)
Where else can you find DNA beside the nucleus of the cell?
Mitochondria
Chloroplast

4. Asexual Reproduction Asexual reproduction
single individual is sole parent and passes copies of all its genes to its offspring
Clone
the offspring of asexual individuals

5. Sexual reproduction
Two parents give rise to offspring with unique combinations of genes; results in more variation

6. Animals Life Cycle Plants and some algae Fungi and some algae
sequence of stages from an organisms conception to production of its own offspring
Animals

7. More Vocab somatic cell: body cells; any cell other than sperm or ovum
karyotype:
micrograph of the 46 human chromosomes in which they are lined up in pairs starting with the longest
homologous chromosomes:
same length, centromere position, staining pattern; carry genes governing the same inherited characters
sex chromosomes:
X and Y chromosomes
autosomes:
all non-sex chromosomes (1 through 22)

8. Karyotype

10. Meiosis and Sexual Reproduction
Sexual Reproduction – chromosomes of two parents combine to form offspring 23 23
+ (N) +
Gametes
Fertilization
(2N) 46
Zygote

11. About Chromosomes
(2N) = diploid – any cell with 2 complete sets of chromosomes
(N) = haploid – a cell with 1 complete set of chromosomes
Zygote (2N) – egg cell after fertilzation = egg + sperm
Each chromosome in egg has a matching chromosome from sperm
Homologous Pairs – matching chromosomes

12. Homologous pairs chromosomes occur in pairs one set from each parent
Diploid or 2N
Cells that contain both sets of chromosomes.
Haploid =1N
Sex cells have only half the chromosome number

13. Just before Meiosis
begins, during
interphase
identical sister
chromatids
are attached at
the centromere, and
centrioles have
been duplicated.
Centrioles

14. Meiosis: Prophase I During Prophase I: chromosomes condense
nucleus breaks down
spindle fibers form
Homologous chromosomes form tetrads (fours)

15. Meiosis: Prophase I the chromosomes condense
centrioles move to opposite poles of the parent cell and begin building the spindle microtubules.
the nuclear envelope breaks down

16. Meiosis: Prophase I Homologous chromosomes pair up, forming tetrads.

17. Meiosis: Prophase I
Homologous chromosomes pair up, forming tetrads...

18. Meiosis: Prophase I …. and crossing over may occur.
Crossing over- pieces of DNA are exchanged with the matching homologous chromosome

19. Meiosis: Prophase I
centrioles begin building the spindle fibers.

20. Meiosis: Prophase I
Spindle fibers grab each chromosome at the centromere.
Move the chromosomes towards the poles.

21. Meiosis: Metaphase I During Metaphase I:
Homologous chromosomes line up in the middle.
Equator = metaphase plate

22. Meiosis: Metaphase I Each pair is assorted independently; this
means that the maternal
homolog in each pair
randomly faces up or down.
And this pair could have assorted
like this.
So this pair could have
assorted like this.

23. Meiosis: Anaphase I During Anaphase I: Homologous pairs of separate.
Sister chromatids remain attached at the centromere.

24. Meiosis: Anaphase I

25. Meiosis: Anaphase I

26. Meiosis: Telophase I During Telophase: spindle fibers break down
new nuclear membrane forms

27. Meiosis: Telophase I
the spindle fibers
break down

28. Meiosis: Telophase I new nuclear membrane forms around each
group of chromosomes

29. Cytokinesis:
Splitting of the cytoplasm

30. Now these two haploid cells will begin Meiosis II; in this division, sister chromatids will separate.

31. Meiosis: Prophase II Meiosis II is very much like Mitosis.
During Prophase II:
nuclear membrane breaks
spindle fibers reform

32. Meiosis: Prophase II
the nuclear membrane breaks down

33. Meiosis: Prophase II
centrioles move to opposite poles of the parent cell and begin building new spindle fibers

34. Meiosis: Prophase II

35. Meiosis: Prophase II
centrioles begin building the spindle fibers

36. Meiosis: Prophase II The spindle fibers
attach to the chromosomes at the centromere

37. Meiosis: Metaphase II The spindle fibers
move the chromosomes to the center (metaphase plate) of the cell.

38. Meiosis: Anaphase II
Sister chromatids separate.

39. Meiosis: Anaphase II

40. Meiosis: Telophase II During Telophase II:
the spindle fiber break down
nuclear membrane reforms around each group of chromosomes

41. Meiosis: Telophase II
the spindle fibers break down

42. Meiosis: Telophase II
new nuclear membrane form around each group of chromosomes

43. Cytokinesis:
Result:
Four non-identical haploid cells are formed.

46. Mitosis vs. Meiosis

47. A comparison of mitosis and meiosis
Mitosis and Mieosis
Chromosomes replicate only once
Mitosis
Cell divides once
Produces 2 identical daughter cells
Meiosis
Cell divides twice
Daughter cells with half the number of chromosomes
Daughter cells are not all alike
Produces 4 cells (gametes)

48. Independent Assortment

49. Crossing Over