1. Cell Reproduction
Chapter 8

2. Chromosomes = rod-shaped structures made of DNA and proteins
Histone = protein that helps maintain the shape of chromosomes and aid in the tight packing of DNA

3. Chromatid = each half of the chromosome, exact copies that have been replicated
Centromere = point where 2 chromatids are attached
Chromatin = DNA that is less tightly coiled

4. Sex chromosomes = determines the sex of an organism; humans have either an X or Y
Autosomes = all of the other chromosomes
Every organism is produced by sexual reproduction has 2 copies of each autosome.
Homologous chromosome = homologues
= same size, shape, and carry genes for same traits

5. Karotype = photomicrograph of chromosomes
= 46 chromosomes exist as 22 homologous pairs of autosomes and 2 sex chromosomes

6. Genetic Disorder
A disease or condition caused by an absent or defective gene or by a chromosomal aberration

7. Diploid = cells having 2 sets of chromosomes (2n)
Haploid = cell having 1 set of chromosomes (1n)
= sperm and egg cells
approximately 2 trillion cells (25 million cells per second) are produced by an adult human body everyday

8. Cell division = process by which cells produce offspring cells
Binary Fission = division of a prokaryote cell into 2 offspring cells
Asexual reproduction = production of offspring from one parent

9. Mitosis = cell division in Eukaryote cells; new cells with genetic material that is identical to the first (original cell)
- Occurs in organisms undergoing growth development, repair or asexual reproduction

10. Cell Cycle
Interphase- time between cell divisions; cell spends most of its time
G1 phase – grow to mature size
S phase – DNA copied (synthesized)
G2 phase – prepares for cell division
Go phase – usually after G1; does not copy DNA, does not divide
Mitosis – nucleus divided
Cytokinesis – cytoplasm divides

11. Stages of Mitosis

12. Prophase shortening & tight coiling of DNA into rod-shaped chromosomes
nucleolus & nuclear envelope breaks down
centrosomes & centrioles appear in animal cells
only centrosomes appear in plant cells
spindle fibers = made of microtubules radiate from centrosomes in preparation of the next phase
mitotic spindle = array of spindle fibers; serves to equally divide chromatids between 2 offspring cells
made up of kinetochore fibers – attached to a disk shaped protein and to one of the chromosomes and polar fibers extend from centrosome to centrosome
Kinetos means moving choros means place

14. Metaphase
kinetochore fibers move chromosomes to center (equator)

15. Anaphase
chromatids separate at centromere & slowly move toward opposite poles

16. Telophase
spindle fibers disassemble; chromosomes return to a less tightly coiled chromatin state
nuclear envelope forms around each set of chromosomes; as well as a nucleolus

17. Cytokinesis (in animals)
begins with the cell membrane pinching inward in the middle between 2 poles (cleavage furrow)

18. Cytokinesis (in plants)
vesicles from Golgi apparatus join together at the midline to form cell plate
cell wall will eventually form from cell plate

19. Checkpoints

20. Meiosis
- process of division that reduces the number of chromosomes in new cells to half the number in the original cell

21. synapsis – pairing of homologous chromosomes

22. Crossing-over = process where portions of the chromosome may break off and attach to adjacent chromatids on the homologous chromosomes
 genetic recombination = a new mixture of genetic material is created

23. Meiosis I

24. Prophase I DNA tightly coils into chromosomes Spindle fibers appear
Nucleolus and nuclear membrane disassemble
Every chromosome lines up next to its homologue (the pairing is called synapsis and each pair is called a tetrad)

25. Metaphase I
The tetrads line up randomly along the dividing cell’s midline
Spindle fibers from one pole attach to the centromere of one homologous chromosome (spindle fibers from opposite pole attached to the other homologous chromosome of the pair)

26. Anaphase I
Each homologous chromosome (consisting of two chromatids attached by a centromere) moves to an opposite pole of the dividing cell (random separation of homologous chromosomes= independent assortment)

27. Telophase I and Cytokinesis I
Chromosomes reach the opposite ends of the cell
Cytoplasm splits
New cells contain haploid number of chromosomes
Meiosis I result: 2 new cells, containing one chromosome from each homologous pair but 2 copies of each because of the “sister” chromatids”

28. Meiosis I

29. Meiosis II

30. Prophase II
Spindle fibers form and begin to move chromosomes toward the midline of the dividing cell

31. Metaphase II
The chromosomes move to the midline of the dividing cell, with each chromatid facing opposite poles of the dividing cell

32. Anaphase II
Chromatids separate and move toward opposite poles of the cell

33. Telophase II and Cytokinesis II
A nuclear envelope forms around the chromosomes in each of the four new cells
Cytoplasm splits in each of the two dividing cells resulting in 4 cells that contain half of the original cell’s number of chromosomes

34. Meiosis II

36. Where are gametes formed in humans??
Males: in the testes
In SPERMATOGENESIS: a diploid reproductive cell divides meiotically to form FOUR haploid spermatids, each of which develop into a mature sperm cell (AKA spermatozoa)
Females: in the ovaries
In OOGENESIS: a diploid reproductive cell divides meiotically to produce ONE mature egg cell (ovum)
Why not four?
During cytokinesis I and II, the cytoplasm of the cell is divided unequally between new cells….one cell receives most of the cytoplasm and therefore it can become the egg. The other three products that will eventually degenerate are called polar bodies

43. Sexual Reproduction
The production of offspring through meiosis and the union of a sperm and an egg
forms a zygote (fertilized egg)
Offspring produced by sexual reproduction are genetically different from the parents because genes are combined in new ways in meiosis