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