2. 2 Types of Cells
o “Body cells” (somatic) vs. reproductive
cells (gametes).
o Examples of somatic cells: skin cell, liver
cell, brain cell, red blood cell…
o Human somatic cells - 46 chromosomes.
o Examples of gametes: egg cell or sperm
cell
o Human gametes - 23 chromosomes.
3. How much DNA is in our cells?
o DNAchromosomes
o How many chromosomes in a human
somatic cell?
o 46 chromosomes or 23 homologous pairs
o What is the origin of these pairs?
o Homologous pair- chromosomes that
carry the same genes
o These cells are diploid.
o The diploid number in humans is 46.
4.
5. How much DNA is in our cells?
o How many chromosomes are in a gamete
(reproductive cell)?
o 23 chromosomes
o Mom and dad pass on one chromosome
from each homologous pair.
o These cells are haploid.
o The haploid number in humans is 23.
6.
7. How are reproductive cells formed?
o Meiosis is nuclear division that produces
haploid gametes.
o Chromosomes - no longer in pairs.
o Each parent passes on one chromosome from
each homologous pair in the gamete.
o Reproductive cells contain half the number of
chromosomes that a somatic cell contains.
o 4623
8.
9. How is Mitosis different from
Meiosis?
MITOSIS MEIOSIS
Chromosome # Chromosome #
stays same reduced half
2 new cells produced 4 new cells produced
Somatic cells Gametes
Identical Variation
10. What are reproductive cells?
o In males reproductive cells originate
from cells called spermatogonium.
o In females reproductive cells (egg cells)
originate from cells called oogonium.
13. Meiosis Errors
o Errors during meiosis cause gametes to be
defective.
o Most common error is called
nondisjunction.
o When nondisjunction occurs, chromosomes
fail to separate correctly.
o Creates gametes (egg/sperm cells) with
too many (trisomy) or too few
chromosomes (monosomy).