1. Long, rod-shaped structures composed of DNA and proteins

Chromosome Structure: Super Coiling of DNA (YouTube Clip—click image)

2. Formed from a single DNA strand that contains MANY genes  NOTE: Gene = a region of DNA that controls a hereditary characteristic (trait)

chromosome = 1-strand of DNA  How many strands of DNA do we have in a normal body cell? Click for size perspective

1.Every species has a set number of chromosomes in each cell 2.Humans have 46 chromosomes in EVERY cell with the EXCEPTION of sex cells

Do you think that the number of chromosomes indicates how highly developed an organism is? Check out other organisms !

1. SEX CHROMOSOMES – chromosomes that determine the sex of an organism – Humans…Normal Female = XX Normal Male = XY – Chromosome pair #23 2. AUTOSOMES All of the other chromosomes in an organism. Chromosome pairs #ed 1-22

Organisms receive one copy of each autosome from each parent The two copies of each autosome are called HOMOLOGOUS CHROMOSOMES

HOMOLOGOUS CHROMOSOMES = chromosomes of the same size, shape, and banding pattern. One chromosome of the pair came from each parent.

1.Haploid (1n) = cells that contain ONE SET of chromosomes (germ cells/sex cells/gametes) 2. Diploid (1n) = cells that contain TWO SETS of chromosomes (somatic cells / body cells)

i.e. When a sperm cell (1n) and an egg cell (1n) combine, the new cell will be diploid (2n)

1. A picture of the chromosomes in a dividing cell 2. Used to examine an individual’s chromosomes

KaryotypeKaryotype Normal Male

KaryotypeKaryotype wise.berkeley.edu/student/topFrame.php?projectID=23132 Karyotype BEFORE Mitosis Karyotype AFTER Mitosis

Haploid cell Diploid cell

WISE is a simple yet powerful learning environment where students examine real world evidence and analyze current scientific controversies through a technology-driven model. The WISE projects are designed to meet national science standards and complement the Central Bucks current science curriculum.

1. Google WISE and choose 2. Choose “Join WISE” 3. Choose create “student account” 4. Register Enter first initial and last name Choose gender Period = 23 Create a password you will remember Student registration code = J13GRU 5. RECORD the username they give you and then log-in

1.Process of nuclear division that reduces the number of chromosomes in new cells to HALF the number in the original cell.

2.Meiosis results in... Sex Cells a.Female gamete = egg cell b.Male gamete = sperm cell Images from:

3.Cells undergo all the phases of interphase  Then they enter MEIOSIS which involves TWO distinct cell divisions Division 1 Division 2 Image from:

1. What happens during interphase? 2. Where in an organism’s body will cells carry out meiosis?

1.Meiosis I a.Prophase I (crossing over) b.Metaphase I c.Anaphase I (homologous chromosomes separate) d.Telophase I and cytokinesis

Portions of chromatids break off and attach to adjacent chromatids on the homologous chromosome  Occurs during Prophase I

Interphase Telophase I Anaphase I Metaphase I Prophase I Cytokinesi s Images from:

2.Meiosis II a.Prophase II b.Metaphase II c.Anaphase II (sister chromatids separate) d.Telophase II and cytokinesis (4 haploid cells)

Coming from Meiosis I Prophase II Metaphase II Anaphase II Telophase II Cytokinesis Images from:

1. When did crossing over occur? 2. When do homologous chromosomes separate? 3. Why are sex cells haploid? 4. When do the sister chromatids separate?

Image from: 1. Meiosis I = separates homologous chromosomes 2. Meiosis II = separates sister chromatids

3. At the end of meiosis II four UNIQUE daughter cells are produced (4 haploid cells)

Complete activities 1 to 4.