Ch. 8 Cell ReproductionWhat is cell division?

Mitosis

What is a zygote?

It forms when the male and female gametes unite.

All cells come from preexisting cells

DNA is inside a rod-shaped structure called a?

Chromosomes

ChromosomesEvery chromosome consists of two identical parts called sister chromatids. Each half is a chromatid.

The point where each chromatid crosses or attaches to the other chromatid is called the centromere.

Chromatids only occur during S phase of interphase.

Every cell has a certain # of chromosomes in the cell. (Pg. 146)

Ex. Humans=46, chicken=78, cat=32, chimp=48, dog=78

Pg. 145 Histones are proteins that DNA wraps around in eukaryotic cells.

Why do all organisms have an even # of chromosomes?Chromosomes are in pairs called homologous chromosomes.A diploid (2N) cell has both chromosomes that make up the homologous pair.A haploid (1N) cell has only 1 half of the homologous pair.Sex chromosomes determine the sex of the offspring (X or Y).Autosomes are all the chromosomes except the sex chromosomes. We have 44 or 22 pair.Karyotype – a map of the chromosomes.

Cell Cycle3 parts to the cell cycle

1. Interphase – resting & growth stage (3 parts – G1, S, & G2)2. Mitosis – cell division (4 parts)3. Cytokinesis- produces 2 daughter cellsPg. 149

There are approximately 100 trillion cells in an average human.Some cells divide every 20 to 30 minutes in a animal embryo.

4 Stages of Mitosis

Prophase – 1st stage of mitosis

Chromosomes start to coil and shorten.

Centrioles form and migrate to each end.

Animals only have centrioles from the centrosomes. Pg. 150

Spindle fibers form between the two centrioles.

Nuclear membrane & nucleolus break down and disappear.

Metaphase

2nd phase of mitosis

The chromosomes are attached to the spindle fibers.

The spindle fibers arrange the chromosomes in a line at the middle of the cell.

Anaphase

3rd stage in mitosis

The centromeres are pulled apart as the spindle fiber shortens and separates the sister chromatids in half.

Now each chromatid is at opposite ends.

Telophase

4th phase of mitosis

The chromatins reach the opposite poles of the cell.

The spindle fiber & centrioles disappear

The chromatids uncoil

The nucleolus reappears and a new nuclear envelope forms around each set of chromosomes.

Cytokinesis

The plasma membrane pinches off and 2 new identical cells are formed.

The 2 new cells are called daughter cells.

Interphase(1st part of the cell cycle)

Resting and growth stageThe chromatins are duplicated in order to form a sister chromatin, which is two identical chromatins.The cell is preparing to undergo mitosis.

Mitosis Video

MeiosisReduction of Division Meiosis

Meiosis I produces 2 daughter cells, each with half the homologous chromosome. Go from one cell with 46 chromosomes (2N) to two daughter cells with 23 (1N) chromosomes. Draw. Pg. 154-155

Meiosis II occurs after meiosis I. The 2 daughter cells divide to produce 4 haploid cells.

These haploid cells are gamete cell, either egg cells or sperm cells.

Meiosis Video

Differences in Meiosis vs. Mitosis

1. Form synapsis in prophase – homologous chromosomes pair up.

Each pair of homologous chromosomes is called a tetrad.

2. Crossing-over occurs when the chromatids twist and reattach to the opposite homologous chromosome in the tetrad. Pg. 154.

3. The outcome of Meiosis I is 2 new cells with half the number of chromosomes as the original cell, but the 2 new cells have two copies of the chromosomes because of replication before Meiosis I.

Meiosis II does not have replication, so the final product is 2 new cells (4 total now) with half the chromosomes (haploid – 1N).

Genetic recombination is the result of crossing-over during prophase/metaphase of Meiosis I. This causes a mixing of genetic material.

Independent assortment – is the random separation of chromosomes during prophase/metaphase of Meiosis I. This causes genetic variation of maternal and paternal chromosomes.

Cell Division Video

Mitosis vs. Meiosis