1. The Cellular Basis of Reproduction and Inheritance
Chapter 8: 1-6,11-18
The Cellular Basis of Reproduction and Inheritance
Rain Forest Rescue- Scientists in Hawaii have attempted to “rescue” endangered species from extinction

2. The goal of these scientists:
Cyanea kuhihewa
The goal of these scientists:
To promote reproduction to produce more individuals of specific endangered plants

3. Life Cycle: sequence of stages leading from the adults of one generation to the adults of the next
In sexual reproduction
Fertilization of sperm and egg produces offspring
In asexual reproduction
Offspring are produced by a single parent, without the participation of sperm and egg

4. 8.1 Like begets like, more or less
Asexual reproduction
Offspring are genetic copies of the parent and of each other
LM 340

5. Sexual Reproduction
Creates a variety of offspring
Chromosomes- structures that contain most of an organisms DNA

6. 8.2 Cells arise only from preexisting cells
Cell division is at the heart of the reproduction of cells and organisms
Cells come only from preexisting cells
Cell division:
Unicellular- cell division produces an entire organism
Some multicellular organisms- reproduce asexually
Sexually reproducing species
Basis of sperm and egg fertilization
Single cell (zygote) development into adult organism
Functions in cell renewal and repair

7. 8.3 Prokaryotes reproduce by binary fission “dividing in half”
Asexual reproduction- the genetically identical offspring inherit their DNA from a single parent
Chromosomes are much smaller than in eukaryotes
Prokaryotic chromosomes

8. Division into two daughter cells
Prokaryotic chromosome
Plasma membrane
Cell wall
Duplication of chromosome and separation of copies 1
Continued elongation of the cell and movement of copies 2
Division into two daughter cells 3 3

9. Eukaryotic Chromosomes
Chromosomes- structures that contain most of an organisms DNA
Duplicate with each cell division
A eukaryotic cell has many more genes than a prokaryotic cell (30,000 vs 3,000)
Grouped into multiple chromosomes in the nucleus
Human body Cells= 46 chromosomes
Dogs= 78 chromosomes

10. As a cell prepares to divide:
Most of the time chromosomes exists as chromatin- diffuse, thin fibers of DNA
As a cell prepares to divide:
Chromatin coils up
Forms compact chromosomes
Visible, once stained, under the light microscope

11. Before a cell starts dividing, the chromosomes replicate
TEM 36,000
Centromere
Sister chromatids
Before a cell starts dividing, the chromosomes replicate
Producing sister chromatids- joined together at the centromere

12. Cell division involves the separation of sister chromatids
And results in two daughter cells, each containing a complete and identical set of chromosomes
A dividing human cell has 46 duplicate chromosomes (92 chromatids)
Once sister chromatids split, they are each referred to as a chromosome
One goes into each new daughter cell

13. Chromosome distribution to daughter cells
Centromere
Chromosome duplication
Sister chromatids
Chromosome distribution to daughter cells

14. 8.5 The cell cycle multiplies cells
100 trillion cells in our bodies
Cell Cycle- orderly series of events that extends from the time a cell is formed until its own division
2 major phases
Interphase (growth)
G1- cell growth
S- grows and copies DNA
G2- grows and prepares for mitosis
Mitotic Phase (M phase)- Duplicated chromosomes are evenly distributed into two daughter nuclei

15. INTERPHASE
S (DNA synthesis) G1 G2
Cytokinesis
Mitosis
MITOTIC PHASE (M)

16. 8.6 Cell division is a continuum of dynamic changes In mitosis:
The chromosomes coil up
A mitotic spindle moves them to the middle of the cell
The sister chromatids then separate
Move to opposite poles of the cell
Two nuclei form (1 at each pole)
Cytokinesis, in which the cell divides in two

17. Centrosomes (with centriole pairs)
INTERPHASE
PROPHASE
PROMETAPHASE
LM 250
Chromatin
Centrosomes (with centriole pairs)
Nucleolus
Nuclear envelope
Plasma membrane
Early mitotic spindle
Centrosome
Centromere
Chromosome, consisting of two sister chromatids
Spindle microtubules
Kinetochore
Fragments of nuclear envelope

18. TELOPHASE&CYTOKINESIS
METAPHASE
ANAPHASE
TELOPHASE&CYTOKINESIS
Spindle
Metaphase plate
Daughter chromosomes
Nuclear envelope forming
Cleavage furrow
Nucleolus forming

19. mitotic cell division functions in:
8.11 Review of the functions of mitosis
mitotic cell division functions in:
Growth
Cell replacement
Asexual reproduction

20. Onion (growth) bone marrow (replacement) & hydra (asexual reproduction)
LM 500

21. MEIOSIS AND CROSSING OVER
8.12 Chromosomes are matched in homologous pairs
The somatic (body) cells of each species contain a specific number of chromosomes
human cells have 46
In metaphase each duplicated chromosome has a “twin”
Making up 23 pairs of homologous chromosomes

22. The chromosomes of a homologous pair
Carry genes for the same characteristics at the same place, or locus
Chromosomes
Centromere
Sister chromatids

23. X and Y chromosomes
Exception of homologous chromosomes
females (XX) homologous pair
males (XY)
Sex Chromosomes- determine sex
Other 22 pairs are called autosomes

24. Have two sets of chromosomes Are diploid (2n) Gametes
8.13 Gametes have 1 set of chromosomes
Somatic Cells
Body cells
Have two sets of chromosomes
Are diploid (2n)
Gametes
Sex cells (eggs and sperm)
With a single set of chromosomes
Are haploid (n)

25. Involve the alternation of haploid and diploid stages
Mitosis and development
Multicellular diploid adults (2n = 46)
Diploid zygote (2n = 46) 2n
Meiosis
Fertilization
Egg cell
Sperm cell n
Haploid gametes (n = 23)
Sexual life cycles
Involve the alternation of haploid and diploid stages
Figure 8.13

26. 8.14 Meiosis reduces the
chromosome number from
diploid to haploid
Meiosis, like mitosis
Is preceded by chromosome duplication
But in meiosis:
The cell divides twice to form four daughter cells

27. The first division, meiosis I
Starts with synapsis- the pairing of homologous chromosomes
In crossing over
Homologous chromosomes exchange corresponding segments
Meiosis I separates each homologous pair
produce two daughter cells, each with one set of chromosomes
Meiosis II is essentially the same as mitosis
The sister chromatids of each chromosome separate
The result is a total of four haploid cells

28. MEIOSIS I: Homologous chromosomes separate
The stages of meiosis
Meiosis I
MEIOSIS I: Homologous chromosomes separate
INTERPHASE PROPHASE I METAPHASE I ANAPHASE I
Centrosomes (with centriole pairs)
Sites of crossing over
Spindle
Microtubules attached to kinetochore
Metaphase plate
Sister chromatids remain attached
Nuclear envelope
Chromatin
Sister chromatids
Tetrad
Centromere (with kinetochore)
Homologous chromosomes separate

29. Prophase l of Meiosis
Sites of crossing over
Spindle
Tetrad: via synapsis
Sister chromatids

30. Chiasma
Tetrad
Centromere

31. The stages of meiosis Meiosis Il
PROPHASE II METAPHASE II ANAPHASE II
TELOPHASE I AND CYTOKINESIS
TELOPHASE II AND CYTOKINESIS
Cleavage furrow
Haploid daughter cells forming
Sister chromatids separate
MEIOSIS II: Sister chromatids separate

32. Mitosis Meiosis Parent cell (before chromosome replication) Meiosis i
Chromosomes align at the metaphase plate
Tetrads align at the metaphase plate
Sister chromatids separate during anaphase
Homologous chromosomes separate during anaphase I; sister chromatids remain together
No further chromosomal replication; sister chromatids
separate during anaphase II
Prophase
Metaphase
Anaphase Telophase
Duplicated chromosome (two sister chromatids)
Daughter cells of mitosis 2n
Daughter cells of meiosis I n
2n = 4
Tetrad formed by synapsis of homologous chromosomes
Meiosis i
Meiosis ii
Prophase I
Metaphase I
Anaphase I Telophase I
Haploid n = 2
Daughter cells of meiosis II

33. 8.16 Varied Offspring
Mutations are original source of genetic variation
Raw material for natural selection
Synapsis and crossing over during prophase
Independent assortment (orientation) of homologous chromosome pairs along the metaphase plate (during metaphase)
Random Fertilization of eggs by sperm

34. Two equally probable arrangements of chromosomes at metaphase I
Combination 1
Combination 2
Combination 3
Combination 4
Gametes
Metaphase II
Two equally probable arrangements of chromosomes at metaphase I
Possibility 1
Possibility 2

35. 8.17 Homologous chromosomes carry different versions (alleles) of genes
at corresponding loci
Genotype- genetic code
Phenotype- physical expression of genotype
Two genes in mice: 2 alleles of each gene
coat color (gene)
brown (C)
white (c)
eye color (gene)
black (E)
pink (e)

36. Brown coat (C); black eyes (E) White coat (C); pink eyes (e)

37. Tetrad in parent cell (homologous pair of duplicated chromosomes)
White
Pink
Meiosis
Black
Brown
Chromosomes of
the four gametes
Eye-color genes
Coat-color genes

38. 8.18 Crossing over further increases genetic variability
Crossing over- the exchange of corresponding segments between two homologous chromosomes
Genetic recombination- from crossing over during prophase I of meiosis
increases variation still further

39. Chiasma
Tetrad
Centromere

40. Tetrad (homologous pair of chromosomes in synapsis)
Chiasma
Tetrad (homologous pair of chromosomes in synapsis)
Breakage of homologous chromatids
Joining of homologous chromatids 3
Separation of homologous chromosomes at anaphasase I 4
Separation of chromatids at anaphase II
and completion of meiosis
Parental type of chromosome
Recombinant chromosome
Gametes of four
genetic types
Recombinant chromosome
Parental type of chromosome