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

2. You have body cells and gametes.
Body cells are also called somatic cells.
Germ cells develop into gametes.
Germ cells are located in the ovaries and testes.
Gametes are sex cells: egg and sperm.
Gametes have DNA that can be passed to offspring.
body cells
sex cells (sperm)
sex cells (egg)

3. Your cells have autosomes and sex chromosomes.
Your body cells have 23 pairs of chromosomes.
Homologous pairs of chromosomes have the same structure.
For each homologous pair, one chromosome comes from each parent.
Chromosome pairs 1-22 are autosomes.
Sex chromosomes, X and Y, determine gender in mammals.

4. Humans have 46 chromosomes 23 from the male parent
Remember…
Humans have 46 chromosomes
23 from the male parent
23 from the female parent
Each set of chromosomes is homologous
Each of the 23 chromosomes from the male parent will “match” with each of the 23 chromosomes from the female parent.
They are homologous chromosomes.

5. How many Chromosomes do Organisms Have?
Body Cell (2n)
Sex Cells (n)
Fruit fly 8 4
Garden pea 14 7
Corn 20 10
Tomato 24 12
Leopard Frog 26 13
Apple 34 17
Human 46 23
Chimpanzee 48
Dog 78 39
Adder’s tongue fern
1260
630
Is there any correlation between organism size and number of chromosomes?
Do animals have more chromosomes than plants?
Is the diploid number always an even number?

6. Body cells are diploid; gametes are haploid.
Fertilization between egg and sperm occurs in sexual reproduction.
Diploid (2n) cells have two copies of every chromosome.
Body cells are diploid.
Half the chromosomes come from each parent.

7. Haploid (n) cells have one copy of every chromosome.
Gametes are haploid.
Gametes have 22 autosomes and 1 sex chromosome.

8. Chromosome number must be maintained in animals.
Many plants have more than two copies of each chromosome.
Mitosis and meiosis are types of nuclear division that make different types of cells.
Mitosis makes more diploid cells.

9. Meiosis makes haploid cells from diploid cells.
Meiosis occurs in sex cells.
Meiosis produces gametes.

10. Sex Chromosomes & Sex Determination
In humans gender is determined by the sex chromosomes.
Non-homologous, 23rd pair.
50% of sperm cells carry X, 50% carry Y.
100% of egg cells carry X.
If the 23rd pair of chromosomes is XX…female, if XY…male.
Which parent determines the gender of the baby?

11. Diploid Remember…. Cell that has both sets of homologous chromosomes.2N
In humans, the diploid number is 46
2N = 46, a full set
Found in body cells (called somatic cells)
Mitosis

12. Haploid Remember…. A cell that has only 1 set of chromosomes. N
In humans, the haploid number is 23
N = 23, half of the full set
Found in gamete cells (egg and sperm)
Meiosis

13. Meiosis