Chapter 8

Objectives:

• Describe the process of cell division.

I. Chromosome Structure

A. What are chromosomes

A. Rod shaped structure made of DNA and proteins.

B. Coiled tightly inside a cell’s nucleus.

C. Consists of two identical halves

A. Chromatid – each half of the chromosome

B. Centromere – point of attachment for chromatids.

C. Chromatin – when DNA uncoils so code can be copied

II. Chromosome NumbersA. Each species has specific number of

chromosomesA. Humans = 46

B. Sex chromosomes – chromsomes that determine sex of organism

A. Can also carry genes for other characteristics

B. Females have 2 “X chromosomes”

C. Males have “X and Y chromosome”

C. Autosomes = all of the other chromosomesA. Homologous chromosomes = 2 copies of each

autosome

Chromosome Numbers of Various Organisms

D. Karyotype

A. Photo of the chromosomes in a normal human

E. Diploid and Haploid Cells

A. Diploid = cells having two sets of chromosomes (2n)

B. Haploid = cells having one set of chromosomes (n)

a. sex cells

a. sperm = male sex cell

b. egg = female sex cell

II. Cell Division in Prokaryotes (no nucleus)

A. Binary fission – division of cell into two exact copies

III. Cell division in Eukaryotes (Euks have nucleus)

A. Mitosis – results in new cells that are identical to the original cell

A. Asexual reproduction – production of offspring from one parent

B. Meiosis – occurs during the formation of sex cells

A. Produces gametes – another name for sex cells

IV. Mitosis

A. Cell cycle – repeating set of events during the life of a cell

A. Interphase – time between cell divisions

B. Mitosis – nucleus divides

C. Cytokinesis – cell divides

Interphase

• Spend most of the cycle

• Stage of cell growth and maturity

Prophase

• 1st phase

• Centrosomes appear

• Nucleus disappears

• Spindle fibers equally divide chromosomes

Metaphase

• Chromosomes line up in the middle

Anaphase

• Chromatids separate toward opposite poles

Telophase

• Spindle fibers disappear

• Nuclear envelope forms around each set of chromosomes

Cytokinesis

• Cleavage furrow starts to pinch in and eventually separate the cell

Mitosis animation

• http://www.sumanasinc.com/webcontent/animations/content/mitosis.html

V. Control of Cell Division

A. Proteins regulate the control of cell division

B. Proteins signal the cell to move on to the next steps of cell division

VI. When Control is Lost = CancerA. Signaling proteins do not function properly

B. Cells divide uncontrollably = Cancer

VII. Meiosis

A. Spermatogenosis – production of mature male gametes

B. Oogenesis – production of mature female cells

C. Cells go through mitosis twice

D. Crossing over – when chromatids break apart can combine with other chromatids

E. Genetic recombination – new mixture of genetic material that is created from crossing over.

F. Independent assortment – random separation of chromosomes

VIII. Sexual reproduction

A. Production of offspring through Meiosis

B. Creates offspring that are genetically different from parents

C. Enables species to adapt to new conditions

A. Example – if a disease strikes a crop of corn, a few plants may have genetic variations that prevent it from dying. These plants will reproduce creating offspring that are also resistant to the disease.