Cell biology/Meiosis

Asexual vs. Sexual Reproduction
Aseuxal Reproduction: New individuals are created when a parent makes an exact copy of itself. Examples of this is in Mitosis, Binary Fission, Budding, etc. Sexual Reproduction: An individual is created when two haploid gametes (sex cells) join together during fertilization. Example: Meiosis.
 * Asexual Reproduction
 * Sexual Reproduction

Karyotype - Display of chromosomes pairs of a cell arranged by size and shape. Homologous chromosomes are a pair of chromosomes with the same length, centromere position, and staining pattern. They both contain genes of same characteristics. Karyotypes can be used to see defect chromosomes and if there are too many/little chromosomes, leading to a genetic disorder.

Sex chromosomes - X and Y chromsomes (not homologous).

Autosomes - Chromosomes that are not sex chromosomes. "See diploidchromosomes.PNG"

Fertilization - Union of haploid sex cells (gametes) --> diploid (zygote) [fertilized egg].

Reproductive Cells
Somatic Cells: Body cells → Chromosome # in humans (2n) = 46 Gametes/Germ Cells: Sex cells → Chromosome # in humans (n) = 23 Homologous chromosomes: This is a pair of chromosomes in which each parent donates 1 chromosome to the pair.
 * Somatic cells are diploid in number meaning they have a full set of chromosomes. Abbreviated as 2N.
 * Gametes are haploid in number meaning they only have half a set of chromosomes.
 * Sperm (n) → Chromosome # = 23
 * Ova = egg (n) → Chromosome # = 23
 * Abbreviated as N
 * Locus - A specific area on the chromosome where a gene is located.

Meiosis
Meiosis is when '''a full set of chromosomes in a cell is cut in half through the separation of homologous chromosomes. This occurs in two parts: Meisois I and Meisois II.''' Spermatogenisis: The creation of four sperm cells through the process of Meiosis. Oogenesis: Creation of an ova (egg) and three polar bodies through Meiosis.
 * You could call Meiosis the "reduction division".
 * Tetrads and Crossing Over
 * When each pair of chromosome pairs with its homologous chromosome they form a structure called a tetrad.
 * Crossing Over - When tetrads are formed, homologous chromosomes may exchange portions of their chromatids (DNA). Results in a production of different sperm and egg (every sperm/egg is unique). Leads to better living conditions and survival of the species.

Meisois II

 * Overall Diagram

Fertilization
When male and female sex cells, or gametes, (n=23) combine to create a diploid zygote (2n=46).

Diversity

 * Crossing over in Prophase I allows the genes to interact with each other.
 * Random Fertilization - Allows any random sperm to fertilize with an egg.
 * Random Alignment of Homologous Chromosomes - Allows the chromosomes to separate, giving away to IA. Gives other hereditary characteritstics a fair chance to take place.

Comparison

 * Why is mitosis necessary?
 * To replace dead, worn out or damaged cells.
 * So that an organism can grow and develop.
 * Why is meiosis necessary?
 * To create gametes (sex cells) necessary for fertilization.
 * Increase genetic diversity in a population.