Biology

• The chromosome consists of two identical halves.
• Each half of the chromosomes is called a chromatid.
• Chromatids form as the DNA makes a copy of itself before cell division.

• Two chromatids of a chromosome are attached at a point. The centromere holds th two chromatids together until they separate during cell division.
• Centromeres are especially important for the movement of chromosomes during cell division.

The less tightly coiled DNA protein complex.

• Chromosomes that determine the sex of an organism and they may also carry genes for other characteristics.
• In humans, sex chromosomes are either X or Y.

• Females- XX
• Males- XY

• All of the other chromosomes in an organism.
• Two of the 46 human chromosomes are sex chromosomes, and the remaining 44 chromosomes are autosomes.

• Two copies of each autosomes or homologuos are called homologous chromosomes.
• they are the same size and shape and carry genes for the same traits.

A photomicrograph of the chromosomes in a normal dividing cell found in a human.

• cells having two sets of chromosomes are diploid.
• Diploid cells have two autsomes for each homologous pair.
• Diploid cell also have two sex chromosomes in animals, including humans and in many other organisms that have sex chromosomes.

Sperm cells and egg cells are haploid cells, which contain only one set of chromosomes. Haploid cells have half the number of chromosomes that are present in diploid cells.

The division of a prokaryote cell into two off-spring cells. The DNA copied resulting in two identical chromosomes attached to the inside of the prokaryotes inner cell membrane.

Results in new cells with genetic material that is identical to the genetic material of the original cell.

The production of offspring from one parent.

• Occurs during the formation of gametes which are haploid reproductive cells.
• Meiosis reduces the chromosome number by half in new cells.

• The time between cell divisions.
• Interphase is divided into three phases and cell divisions is divided into two phases.

The division of the cell's cytoplasm

The first phase of mitosis.

Made of microtubules radiate from the centromeres in preparation for metaphase.

In plant cells, vesicles from the Golgi apparatus join together at the midline of the dividing cell to form a cell plate.

• Proteins at this checkpoint control whether the cell will divide.
• If teh cell is healthy and has grown to a suitable size during the G1 phase, proteins will initiate DNA synthesis (the s phase.)

• DNA repair enzymes check the results of DNA replication.
• If this checkpoint is passed proteins will signal the cell to begin the molecular processes that will allow the cell to divide mitotically.

If a cell passes this checkpoint proteins signal the cell to exit mitosis. The cell then enters into the G1 phase, the major growth phase of th cell cycle once again.

The pairing of homologous chromosomes which does not occur in mitosis.

Each pair of homologous chromosomes.

Portions of chromatids may break off and attach to adjacent chromatids on the homologous chromosome.

When crossing over permits the exchange of genetic material betwen maternal and paternal chromosomes, genetic recombination results because a new mixture of genetic material is created.

• The random separation of the homologous chromosomes.
• - Results in genetic variation.