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Class lecture notes presented on powerpoint. Material is intended for middle school through high school and can be adjusted as needed. Topics covered include; structure of a chromosome, chromosome number, mitosis, and the cell cycle.
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Genetic Information
Genetic information is carried on genes
A gene is… 1 molecule of DNA contains
thousands of genes DNA=chromatin when the cell is not
dividing (not visible under a microscope)
Mitosis
http://www.johnkyrk.com/mitosis.html
Chromosome Structure
DNA (chromatin) replicates at during cell division preparation = 2 identical chromatids
2 chromatids coil, condense and join together at the centromere = chromosome (now visible under a microscope)
Chromosome Number
Every species has a characteristic # of chromosomes
Chromosomes occur in pairs (code for same info – one from ea. Parent) = homologous pairs
A cell that contains both members of the homologous pair are called diploid – 2N
Chromosome Number cont.
A cell that contains only one member of the homologous pair is called haploid – 1N
In humans: Diploid number is 46 (somatic cells) Haploid number is 23 (gametes)
Frequency of cell division
Varies drastically among different cell types Bacteria – every 20 minutes Human embryo - 15-20 minutes Human skin – every 2 weeks Liver cells – approx. every 18 months
Frequency of cell division
Some cells do not divide after a certain age Liver cells Intestinal cells Nerve cells
Type of cell division
Asexual
Sexual
Asexual Reproduction Making of new cells by mitosis Offspring are exact replica of parent Only one parent
Occurs in: Unicellular organisms as a means of
reproduction Lower plants and animals as a means of
reproduction Most somatic cells of multi-cellular
organisms
Asexual Reproduction
Advantages Simple Fast Low energy output Large number of offspring Daughter cells are identical to parent
cells
Asexual Reproduction
Disadvantages No variation among offspring
Sexual Reproduction
Making of new gametes by meiosis Involves the combining of gametes
from 2 different parents Gametes fuse to form a zygote
(fertilized egg) Chromosome number in gametes is
1N to ensure constant chromosome number on future generations.
Sexual Reproduction
Advantages Variation among offspring
Sexual Reproduction
Disadvantages More complicated Must find mate High energy cost Fewer offspring (generally)
The Cell Cycle
The life of a eukaryotic cell is diagramed as a cell cycle
A repeating sequence of growth and division
5 phases
The Cell Cycle
Interphase : 3 phases G1 Phase:
S Phase :
G2 Phase:
The Cell Cycle
Mitosis - NUCLEAR DIVISION -4 phases Prophase:
Centrioles Spindle fibers Nucleolus Nuclear membrane
The Cell Cycle
Metaphase Fibers push chromosomes to line up
along the equator of the cell
The Cell Cycle
Anaphase Fibers shorten and pull chromatids apart
to opposite sides of the cell.
The Cell Cycle
Telophase Spindle fibers Chromatids Nuclear membrane nucleolus
The Cell Cycle
Cytokinesis: CYTOPLASM DIVISION Not a phase of mitosis
Cytoplasm and organelles separate Usually begins in early anaphase Cytoplasm pinches in In plant cells, a new cell wall is formed
between the 2 new cells – cell plate
