Part II CHROMOSOMES complexes of DNA and protein

CHROMOSOMES… -complexes of DNA and protein. -Chromosomes are the package for DNA and genes.

Cells in the body of sexually producing organisms can be… SOMATIC CELLS -body cells

Fertilization restores the diploid number. + Egg is “n” = haploid Sperm is “n”

A picture of all the chromosomes in a somatic cell is a karyotype. A

Organism Chromosome # Human 46 Corn 20 Yeast 32 Onion 16 Cow 60 Lily

CELL CYLE A cell goes through a cell cycle, going through stages of growth

Stages of the Cell Cycle 1. Interphase: sometimes called the “resting phase. ” This

2. Mitosis: cell divides to produce two daughter cells with the same chromosome number

Important points to remember: a. Chromosomes condense for easy separation [no tangling]. b. Spindle

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Part II

CHROMOSOMES… -complexes of DNA and protein. -Chromosomes are the package for DNA and genes. -duplicated before the cell divides. -chromosome number is specific for each species. A human cell has 46 [or 23 pairs] while a fruit fly has 8 [or 4 pairs]. centromere sister chromatids

Cells in the body of sexually producing organisms can be… SOMATIC CELLS -body cells -contain the DIPLOID [2 n] chromosome number. -produced through MITOSIS. -examples: muscle cell, nerve cell, stomach cell. GAMETES -sex cells -contain the HAPLOID [n] chromosome number. -produced through MEIOSIS. -examples: sperm cell and egg cell

Fertilization restores the diploid number. + Egg is “n” = haploid Sperm is “n” = haploid ZYGOTE is 2 n. Repeated mitosis ultimately leads to the development of multicellular organism.

A picture of all the chromosomes in a somatic cell is a karyotype. A human karyotype reveals 23 pairs of chromosomes. Each pair is called a homologous pair. The 23 rd pair is easy to spot [unequal in size]. They are the sex chromosomes, called X and Y.

Organism Chromosome # Human 46 Corn 20 Yeast 32 Onion 16 Cow 60 Lily 24 Dog 78 Donkey 62 Chicken 78 Earthworm 36 Toad 36 Pig 38

CELL CYLE A cell goes through a cell cycle, going through stages of growth and division.

Stages of the Cell Cycle 1. Interphase: sometimes called the “resting phase. ” This refers to the stage in the life of a cell when it is not dividing. -made up of these sub-stagesa. G 1 - cells grow in size, cells get ready for DNA synthesis. b. S-phase- DNA replication occurs at this stage. c. G 2 - cell continues to grow and make proteins.

2. Mitosis: cell divides to produce two daughter cells with the same chromosome number as the parent cell. This stage takes only from 1 -2 hours.

Important points to remember: a. Chromosomes condense for easy separation [no tangling]. b. Spindle fibers attach to the centromeres, controlling chromosome movement. c. Sister chromatids separate during anaphase. d. Cytokinesis [division of cytoplasm and other cell contents] happen during telophase.