The Cell Cycle These notes are an introduction to The Cell Cycle Unit.

Chromatin-DNA and proteins found in the nucleus of a cell that IS NOT dividing Chromosome-highly coiled DNA and histone proteins found in a cell that IS dividing –Eukaryotic Chromosomes are linear or rod- shaped –Prokaryotic Chromosomes are circular

Chromatid-half of a chromosome Centromere-holds two chromatids together Homologous Chromosomes- chromosomes that are the same size and contain the same gene sequence

2 Types of Chromosomes –Sex Chromosomes-chromosomes that determine the sex of an organism Humans have one pair of sex chromosomes per cell (one pair=two individual sex chromosomes) Human Females=XX Human Males=XY –Autosomes-chromosomes that carry all the other genetic information Humans have 22 pairs of autosomes per cell (22 pairs=44 individual autosomes)

Human cells have a total of 23 pairs of chromosomes (23 pairs=46 individual chromosomes) If a person has too many or too few chromosomes there are severe consequences. Karyotype-a photograph of the chromosomes of an organism; can be used to diagnose specific genetic disorders and to determine the sex of an organism

Diploid Cells –Have the complete set of genetic information –Have 2 of each chromosome –Are somatic cells (body cells-ex. Skin cells) –Human Diploid # = 46 Haploid Cells –Have half the genetic information –Have 1 of each chromosome –Are gametes (sex cells-ex. Sperm and egg) –Human Haploid # = 23