Fertilization The process of haploid gametes joining together to form a diploid cell with 2n chromosomes. n chromosomes come from the male parent and n chromosomes come from the female parent.

Meiosis Meiosis is the cell division process that occurs only in reproductive cells. One diploid cell produces four haploid cells that are not genetically identical. Cells produced by meiosis are gametes and are used for sexual reproduction.

Gamete A cell that joins with another cell during fertilization in organisms that reproduce sexually Gametes are haploid cells and carry only half the DNA of a normal cell.

Crossing Over The exchange of chromosome segments between a pair of homologous chromosomes during Prophase I of Meiosis. This produces a cell that is not a perfect duplicate of the original cell.

Haploid A haploid cell has only one set of chromosomes (n). In humans, this cell has 23 chromosomes. An example of a haploid cell is a gamete. When haploid cells merge, they form a new cell that has half the DNA from one parent and half from the other

An example of a human diploid cell is a zygote. A diploid cell has twice the number of chromosomes (2n) that a haploid cell has. Diploid cells have 46 chromosomes An example of a human diploid cell is a zygote.

Homologous Chromosome A homologous chromosome is one of two paired chromosomes (one from each parent) that carries genes for a specific trait. During Metaphase I of Meiosis, the homologous chromosomes line up at the cell’s equator and then cross over.

Two identical copies of a chromatid. Sister Chromatid Two identical copies of a chromatid. Sister chromatids contain identical DNA. During the Metaphase step of Mitosis, it is the sister chromatid that line up at the cell’s equator.

A picture of all the chromosomes from an individual’s cells. Karyotype A picture of all the chromosomes from an individual’s cells. It is a test used to check for chromosome abnormalities.

Nondisjunction can create disorders such as Down syndrome is the failure of chromosome pairs to separate. This results in gametes with an incorrect number of chromosomes. Nondisjunction can create disorders such as Down syndrome

Autosomes are chromosomes that are not sex chromosomes. Autosomes have chromosome pairs that are identical to each other, but different from other chromosomes.

Sex Chromosome (X & Y) A pair of chromosomes in the germ cells of most animals and some plants, that combine to decide the sex and sex-linked characteristics of an individual. Sex Chromosomes are usually labeled X or Y An XX combination results in a female offspring An XY combination results in a male offspring