Chapter 10 10:1 Cell Reproduction and Cell Division

I Chromosomes A. Structure: Rod shaped structures that are made up of DNA and are found in the nucleus of every cell. 1. DNA – A nucleic acid that contains genetic material and is found on the chromosomes, in the nucleus of every cell. 2. Double Helix - The shape of a DNA molecule. 3. Histones – structures on a DNA molecule that DNA wraps around, these structures help aid in the tightly packing of DNA. 4. NON – histones – Do not participate in the packing of DNA.

Chromatids Each chromosomes is made up of 2 identical halves called Chromatids. Centromeres – each chromatid pair is connected together by a centromere. Each chromatid pair will split during cell division.

2. Chromosomes Numbers A. Sex chromosomes – determine the gender of an organism. 1. XX – female, an egg cell only contains ONE “X” (sex chromosome) 2. XY –Male, a sperm can carry either an X or a Y chromosome. The sperm determines the gender of the organism. B. Autosomes – all other chromosomes in the nucleus except the 2 sex chromosomes. 1. 2 of the 46 in human sex cells, egg and sperm, are sex chromosomes, the other 44 chromosomes are Autosomes.

3. Homologous Pairs A. Every autosome chromosome has an identical pair or twin, one from each parent. When the egg is fertilized by the sperm the 2 sets of 23 chromosomes immediately begin looking for their identical twin to pair up together. (ZYGOTE) 1. These pairs are called homologous pairs. B. Karyotype 1. A visual of all the chromosomes in the nucleus of a dividing cell. C. Body cells – Human body cells all contain 23 pairs of chromosomes. D. Sex cells – human sex cells contain only 23 total chromosmes.

4. Diploid and Haploid Cells A. Diploid – cells that have 2 sets of chromosome. (2n) B. Haploid – Cells that have only one set of chromosomes. (n) such as sperm and egg. 1. 2 haploids together form a diploid cell.