MAKING NEW CELLS Ch 1-2 page 10

 Replicationthe process of copying DNA  Chromosomeis made of a single piece of DNA, which has been supercoiled and organized around various proteins. It's the dense form of DNA and seen just prior to cell replication.  Chromatidis half of a replicated chromosome. When the chromosome replicates, it results in the well known X shape. The X contains two copies of the same DNA. Two sister chromatids are attached at the centromere to make up a replicated chromosome. The sister chromatids separate when the cell divides.

 Mitosisproduces two daughter cells that are exact replicas of the original cell - cloning (23 pairs of chromosomes in each new cell). This is done for growth and repair. Diploid or two. Makes It Two M-i-t (makes twins)  Meiosisproduces gametes (egg and sperm cells) each has only 23 single chromosomes. Haploid or Half. When a sperm and egg combine the result is a new cell with 23 pairs of chromosomes, half from the mother and half from the father. m-E-iosis + s-E-x (Egg and Sperm)

 Interphasereplication of the DNA to become double stranded  Prophasedouble stranded chromosomes become visible (condense)  Metaphasechromosomes line up at the middle of the cell  Anaphasethe chromosomes split and move to opposite ends of the cell  Telephasethe two new nuclei form - each with the diploid number of chromosomes eg in humans 23 pairs  Cytokinesismembrane forms that splits the two nuclei and the cell pinches into two new fully functional daughter cells - clones of the original.

CHROMOSOMES  Autosomes22 pairs of human homologous chromosomes (are not sex determining) - homologous means ideally they are exact replicas.  Sex chromosomesPair 23 has either 2 X's in the case of females and an X and a Y for a male

 Diploid23 pairs of chromosomes (body cells)  Haploid23 single chromosomes (sex gamete cells)

ASEXUAL AND SEXUAL REPRODUCTION  Asexual reproductioncloning - no mixing of genetic material as there is only one parent. Produces off spring that are ideally suited to the current environmental conditions.  Sexual reproductiongenetic material is supplied by both parents and the offspring take on some characteristics of both parents - more variable and responsive to changes in the environment.