Defined: Tightly coiled DNA Form when cells divide –Chromosomes created for the new cells 2 Parts: –1) Chromatids: two identical parts of a chromosome –2) Centromere: Joins chromatids together

Figure  m Centromere Sister chromatids

Cellular Organization of the Genetic Material All the DNA in a cell constitutes the cell’s genome A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells) DNA molecules in a cell are packaged into chromosomes © 2011 Pearson Education, Inc.

Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus Somatic cells (non-reproductive cells) have two sets of chromosomes Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells © 2011 Pearson Education, Inc.

Concept 12.1: Most cell division results in genetically identical daughter cells Most cell division results in daughter cells with identical genetic information, DNA The exception is meiosis, a special type of division that can produce sperm and egg cells © 2011 Pearson Education, Inc.

Overview: The Key Roles of Cell Division The ability of organisms to produce more of their own kind best distinguishes living things from nonliving matter The continuity of life is based on the reproduction of cells, or cell division © 2011 Pearson Education, Inc.

In unicellular organisms, division of one cell reproduces the entire organism Multicellular organisms depend on cell division for –Development from a fertilized cell –Growth –Repair Cell division is an integral part of the cell cycle, the life of a cell from formation to its own division

Figure 12.2 (a) Reproduction (b) Growth and development (c) Tissue renewal 20  m 100  m 200  m

Figure Chromosomes Chromosomal DNA molecules Centromere Chromosome arm Chromosome duplication (including DNA replication) and condensation Sister chromatids Separation of sister chromatids into two chromosomes 1 2 3

Diploid Cells = Cells with the full set of chromosomes –Paired chromosomes Half of our chromosomes come from each parent (23 from each parent) Somatic (non-sex) cells are diploid Created by mitosis Ex: Skin, Muscle, Nerve, Blood Cells

Haploid Cells = Cells with ½ the total number of chromosomes Gametes (sex cells) are the only haploid cells –Ex: Sperm, Egg, Pollen Created by meiosis –Chromosome number reduced by 1/2 How do humans get 46 chromosomes? Haploid sperm cell (23) + Haploid egg cell (23) = Diploid zygote (46)

Defined: Picture of an individuals chromosomes –Help identify sex & chromosome defects Size of final pair identifies sex –Same size: XX = female –Different size: XY = male Normal human will have 46 chromosomes

How many chromosomes are in brain cells? Remember…Brain cells are non-sex cells… …Somatic cells are non-sex cells… …Somatic cells are diploid… …Diploid cells have the full set of chromosomes Answer = 46

How many chromosomes are in female egg cells? Remember…Egg cells are sex cells… …Sex cells are gametes… …Gamete cells are haploid… …Haploid cells have ½ the set of chromosomes Answer = 23

Down Syndrome: What’s Wrong? Writing notation: –1 st : total chromosome # –2 nd : Sex chromosomes –3 rd : extra or missing Down Syndrome 47,XY,+21

Turner’s Syndrome: What’s Wrong? Write the notation for Turner’s Syndrome. 45, X, -23 or 45, XO, -23

Klinefelter’s Syndrome: What’s Wrong? Write the notation for Klinefelter’s Syndrome. 47, XXY, +23

Diploid vs. Haploid Karyotypes