1. KEY CONCEPT Gametes have half the number of chromosomes that body cells have.

2. There are 2 main types of cells in your body:
Body cells and gametes.
There are 2 main types of cells in your body:
1) Somatic Cells- called body cells (soma=body), cells that make up your tissues and organs
DNA in Somatic cells don’t pass on to offsring.
2) Germ Cells-cells in your reproductive organs, ovaries and testes, that develop into Gametes.
Gametes- are sex cells
Ova-egg cells in females
Spermatozoa-sperm cells in males
DNA in Gametes ARE passed on to offspring

3. body cells
sex cells (sperm)
sex cells (egg)

4. Autosomes and sex chromosomes.
Humans have 46 chormosomes, 23 pairs.
Each pair is called a homologous pair. (having the same structure)
For each homologous pair, one chromosome comes from each parent.
Chromosome pairs 1-22, these are called autosomes (homologous).
Pair 23 are called sex chromosomes, humans and most mammals use an XY system for determining sex.

5. Diploid cells and Haploid cells.
Fertilization- joining of egg and sperm occurs in sexual reproduction
Nucleus from both egg and sperm join to form one.
Somatic cells and gametes have different #’s of chromosomes.
Somatic Cells are diploid. (means double)
Gametes are haploid. (means single)

6. Diploid Cells- are cells that have two copies of each chromosome.
One copy from Mom
One copy from Dad
Diploid cells are represented as 2n

7. Haploid cells- are cells have only one copy of every chromosome.
Each human egg and sperm contain 22 autosomes and 1 sex chromosome.
In the egg the sex chromosome is always X
In the sperm the sex chromosome is either X or Y
Maintaining the correct # of chromosomes is vital for the survival of the organism.

8. Somatic cells go through the process of mitosis.
Mitosis is used for growth, repair, and reproduction in some asexual species.
Mitosis makes more diploid daughter cells.
DNA is copied once and divided once

9. Gametes go through a process called Meiosis.
Meiosis-is nuclear division that divides a diploid cell into a haploid cell.
Meiosis produces gametes (diploid)
DNA is copied once and divided twice.
Sometimes called “reduction division”