Chromosomes, The Cell Cycle and Mitosis. Cells. Genes. Nucleus. Organism. Chromosomes. DNA. Chromosome. A structure that forms when DNA wraps around proteins and coils up. Chromosomes only form right before the cell is going to divide. Each half of a chromosome is called a chromatid.
Sister chromatids are identical to each other.
Chromatids are joined at a centromere.
Gene: Segment of DNA found on a chromosome.
Each gene codes for a specific traits.
Each chromosome has many genes on it.
Ex: Drosophila melanogaster (fruit flies) : 8
Homo Sapiens (human): 46
Podocnemis uuiilis (turtle): 28
Karyotype - A karyotype is a picture of all of the chromosomes in the cell of an individual, taken right before the cell divides.
Humans: 22 Pairs of Autosomes, 1 Pair of Sex Chromosomes
Point Mutations (occur in the DNA on the genes)
B. Deletion – substraction of genes
C. Substitution – a different is gene is put in place
D. Translocation – genes are switched around
Chromosomal Mutations (occur in the genes on the chromosome)
(including small penis, tall physique, enlarged breast tissue and
All somatic cells undergo the cell cycle in order to prepare for cell division (mitosis)
Mitosis is a form of asexual reproduction. The cells that form as a result of mitosis are clones (identical copies) of the original cell.
Why do our cells need to divide????
1. Growth of the organism
2. Repair of cells or replacement of “dead” cells
Chromosomes needs to be copied before a cell divides, so that each new cell has the correct amount of DNA and the correct number of chromosomes.
Interphase is the first 3 phases of the cell cycle together
G1, S and G2
Cells carrying on normal activities
The cell has checkpoints to ensure that each phase was completed correctly.
G1: is the cell big enough
S/G2: did the DNA copied correctly
Mitosis (and Cytokinesis): making sure the cell divided correctly.
Checkpoints not working and the cell dividing uncontrollably can lead to cancer.
Give each student has a copy of the “Understanding Cancer” worksheet from the NIH: Cell Biology and Cancer curriculum guide. This is available online at: http://science.education.nih.gov/supplements/nih1/cancer/guide/pdfs/ACT2M.PDF
(To see the entire Cell Biology and Cancer curriculum guide, go to http://science.education.nih.gov/supplements/nih1/cancer/default.htm)
Use a computer and projector to show students the 5 animations available online at: http://science.education.nih.gov/supplements/nih1/cancer/activities/activity2_animations.htm
Before G1 –
After S –
92 chromatids (46 chromosome pairs)
After mitosis –
2 cells each with 46 chromatids!!
Daughter cells are identical to the parent cell!!!