1. Genetics--Nuclear Division & Inheritance
Mitosis & Meiosis

2. Introduction What is Genetics?
What level of organization is being examined?
molecular, cellular, species, or population
What is the purpose of this lab?

3. Somatic versus Reproductive Cells
Somatic cells:
all except the reproductive cells
2 copies of each chromosome
diploid
example: in humans, the diploid number is 46
Reproductive or sex cells:
haploid
1 copy of each chromosome

4. Nuclear Division Mitosis prior to mitosis chromosomes are duplicated
nuclear division in somatic cells
genetic info from “parent” to daughters
cancer: uncontrolled cell division

5. Nuclear Division Meiosis prior to meiosis: chromosomes are duplicated
nuclear division in the sex cells
genetic diversity

6. Cytokinesis division of the cytoplasm occurs at the end of mitosis
occurs at the end of meiosis I
occurs at the end of meiosis II

7. Interphase
Mitosis

8. Interphase no nuclear or cell division
DNA replication, chromosome duplication, and cell growth
“chromosomes,” not visible inside nucleus
but can see nucleolus inside nucleus

9. Mitosis Four phases of mitosis: prophase metaphase anaphase telophase
End result of mitosis: 2 daughter cells

10. Prophase
Duplicated chromosomes condense and become visible as sister chromatids joined at the centromere
nuclear membrane disintegrates; neither the nucleus nor the nucleolus is distinct
spindle apparatus of the cell is formed

11. Prophase Chromatin condenses into discrete chromosomes
two identical “sister chromatids”
joined at the centromere
Early prophase
Prophase

12. Metaphase
Chromosomes are aligned along the cell’s equator at their centromeres
spindle fibers are visible

13. Metaphase
Chromosomes convene on the metaphase plate, an imaginary “equator” located between the two poles of the spindle. Centromeres are aligned, and sister chromatids of each chromosome straddle the metaphase plate.
Metaphase plate
Spindle fibers

14. Anaphase Migration of the chromosomes: Each chromatid -- a chromosome
centromeres split
move along the spindle fibers towards opposite poles
pulling the sister chromatid
Each chromatid -- a chromosome

15. Anaphase
The sister chromatids separate from each other and move along the spindle fibers towards opposite poles. Each chromatid is now considered a chromosome.
Spindle poles
Early anaphase
Anaphase

16. Anaphase
By the end of anaphase, each pole has an equivalent and complete set of chromosomes.
Late anaphase

17. Telophase
Chromosomes are aggregated at the poles and begin to thin out and extend in length
new nuclear membrane forms; nucleolus and nucleus begin to reappear
spindle disintegrates
cytoplasm divides (cytokinesis occurs); daughter cells begin to form

18. Telophase The “daughter” nuclei begin to form at the two poles
Nuclear membranes begin to form
chromosomes lose their distinct appearance.
Telophase
Cytokinesis begins, separating the cytoplasm into 2 “daughter cells”.
Late telophase

19. Telophase formation of 2 daughter cells
Each daughter cell has same genetic material as parent
Daughter Cells

20. Meiosis: Reproductive or Sex Cells
Gametes
female gametes: “eggs” or “ova” (ovum, singular)
male gametes: “sperm”
HAPLOID, have 1 copy of each chromosome (i.e., 1/2 as many chromosomes as somatic cells)
example, in humans, the haploid number is 23.

21. Meiosis in the Lily Anther
male reproductive organ in flowering plants.
meiosis takes place
result: haploid pollen grains

22. Meiosis in the Lily Anther
A very thin cross-section of a lily anther
stain it
examine with a compound light microscope:

23. Meiosis in the Lily Anther
Each anther contains 4 pollen sacs where meiosis takes place.

24. Meiosis in the Lily Anther
Study the various phases of meiosis in prepared slides of the lily anther.
look at the cells inside the pollen sacs
locate the different phases.

25. Stages of Meiosis Meiosis I: Meiosis II:
Meiosis consists of meiosis I and meiosis II and both have 4 stages leading up to the actual cell division.
Meiosis I: Meiosis II:
Prophase I Prophase II
Metaphase I Metaphase II
Anaphase I Anaphase II
Telophase I Telophase II

26. Meiosis: Prophase I
Chromatin condenses into discrete chromosomes. Chromosome is actually composed of 2 sister chromatids.
Homologous chromosomes come together as pairs.

27. Meiosis: Metaphase I
Metaphase plate
Chromosomes are arranged on the metaphase plate, still in homologous pairs.
Spindle fibers from each pole attach to one chromosome of each pair of the homologue.
Spindle fibers

28. Meiosis: Anaphase I
each homologous pair of chromosomes separate and move toward opposite poles.
each chromosome still consists of 2 sister chromatids joined together at the centromere.

29. Meiosis: Telophase I Chromosomes have moved to opposite poles.
Cytokinesis separates the cytoplasm into 2 daughter cells.
Each cell is now haploid.
Haploid
Haploid

30. Meiosis: Prophase II
In prophase II, the chromatin again condenses so the chromosomes have a distinct shape.

31. Meiosis: Metaphase II
In metaphase II, chromosomes align on the metaphase plate.

32. Meiosis: Anaphase II
sister chromatids separate, and move towards opposite poles
sister chromatids are now individual chromosomes.

33. Meiosis: Telophase II
nuclei begin to form at opposite poles, and cytokinesis occurs
4 daughter cells, each with the haploid number of chromosomes.
Haploid
Haploid
Haploid
Haploid

34. Meiosis I: Review
Prophase I
Metaphase I
Telophase I
Anaphase I

35. Review: Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II

36. Chromosomes and Genes one long strand of DNA associated proteins
“chromatin”
thousands of genes
gene
discrete unit of heredity
locus
physical location of a gene

37. Homologous Chromosomes, Genes, and Alleles
Chromosome pair:
“homologous chromosomes”
pair has genes at the same loci
“alleles”
may be the same or different

38. Human Genetics Genotype Phenotype
heterozygous
homozygous
Phenotype
Observe traits and identify which form you possess
Make a table

39. Heredity and Genetic Disorders
Video, “Healthy, Heredity, and Genetic Disorders”
Extra 21st chromosome

40. Mechanics of Mitosis Answer questions
use instructional materials available
video: Mechanics of Mitosis
posters
Photo Atlas of Biology

41. Mitosis in the Onion Root Tip
Today’s lab exercises
examine the tip of an onion root
find and identify the 4 different phases of mitosis.
Root tips are useful material because the cells are frequently dividing as the root grows.

42. Growth and Mitosis in Onion Root Tips
A) Examine onion (Allium) root tip under low power objective (10x)
answer questions
B) Examine same slide under high power objective (40x)
follow instructions

43. Meiosis: The basis of Genetic Inheritance and Sexual Reproduction
Mechanics of Meiosis
Answer questions
use instructional materials available
video: Mechanics of Meiosis
posters
Photo Atlas of Biology

44. Meiosis and Gamete Formation in Lily Anthers
Observe first and second meiotic division in demonstration slides
Note:
DO NOT move the slides out of position
Use only FINE focus