Meiosis and Fertilization

Flashcards about meiosis and fertilization.

Human Karyotype

A regular human cell has 46 chromosomes, 44 autosomes which come in pairs, and 2 sex chromosomes (male usually XY, female usually XX).

Homologous Chromosomes

Pairs of autosomes that have all of the same genes arranged in the same order, but there are small differences in the DNA letters of the genes.

Homologous Chromosomes in body cells

Have the same length and same centromere position, carry genes that control the same inherited traits.

Importance of proper number of chromosomes

Cells divide to make more cells (mitosis), reproductive cells divide (meiosis), and reproductive cells join to make a new individual (fertilization).

Mitosis

Before a cell divides, it copies all of its chromosomes; these copies, called sister chromatids, are identical and held together by centromeres.

Meiosis

A special type of cell division that reduces the number of chromosomes by half and creates genetic diversity.

Meiosis vs. Mitosis

Homologous chromosome pairs line up and exchange pieces, a process called recombination (crossing over).

Independent assortment

Homologous pairs line up in random orientations at the middle of the cell as they prepare to separate.

Fertilization

Egg and sperm cells have just 23 chromosomes each; through fertilization, egg and sperm join to make a cell with 46 chromosomes (23 pairs), called a zygote.

Genes

One homologous chromosome came from each parent; they have the same genes arranged in the same order, but there are small variations in the DNA letters of those genes.