Chromosomes
and Meiosis
Unit
Cell Types
1) Somatic Cells (aka: body cells)
- are diploid (2n)
- DNA not passed on
Cell Types
2) Gametes (aka: sex cells)
- ex: ova (egg) and
spermatozoa (sperm)
- are haploid (1n)
- DNA passed on
Egg and Sperm Comparative Size
Diploid vs. Haploid
Diploid cells have two
copies of each
chromosome: one copy
from the mother and
one from the father.
Haploid cells have only
one copy of each
chromosome
Look at the following
chromosome numbers of
these living things.
Do you notice anything
about the numbers?
Chromosome Numbers of Various
Living Things
Algae
148
Kangaroo
12
Shrimp
254
Hedgehog
90
Cow
60
Mosquito
6
Deer
70
Giraffe
62
Dog
Earthworm
78
36
Pigeon
Tiger
80
38
Turkey
Horse
82
64
Cabbage
Carp
18
104
Chromosomes
Each species has a
characteristic number of
chromosomes
That fact prevents this from
happening
That fact allows this to happen
That fact allows this to happen
That fact allows this to happen
Mule = male donkey and a
female horse
That fact allows this to happen
Liger
Tigon
Chromosomes (cont)
Types
1) Autosomes
2) Sex Chromosomes
- female = XX
male = XY
The sex of some species is
determined by the temperature of
the environment during incubation
(mostly occurs in reptiles)
Chromosomes (cont)
Humans have 46 chromosomes
(23 pairs)
- 44 autosomes (22 pairs) and
2 sex chromosomes (1 pair)
- a diploid # (2n) of 46 and a
haploid # (1n) of 23
Karyotype = picture of an
individual’s chromosomes
Homologous Chromosomes vs.
Sister Chromatids
Homologous Chromosomes =
two separate chromosomes,
one from mom and one from
dad
- very similar in size and carry
the same genes, but they are
not copies of one another
Homologous Chromosomes vs.
Sister Chromatids (cont)
In contrast, each half of a
duplicated chromosome is called a
chromatid
- together, the two chromatids are
called sister chromatids
- thus, sister chromatids refers to
the duplicated chromosome that
remain attached (by the
centromere)
Homologous Chromosomes
Homologous
chromosomes
(shown
duplicated) are
two separate
chromosomes –
one inherited
from the mother
and one from
the father
Sister
Chromatids
Sister
Chromatids
Homologous Chromosomes vs.
Sister Chromatids (cont)
Homologous chromosomes
split in Meiosis I
Sister chromatids split in
Meiosis II
Meiosis
= a form of nuclear division
that divides a diploid cell into
a haploid cell
- makes egg and sperm
- 2 rounds of division (Meiosis I
and Meiosis II)
Meiosis (cont)
Meiosis I – divides
homologous chromosomes
Meiosis II – divides sister
chromatids
The overall process
produces haploid cells.
Meiosis I
Meiosis II
Gametogenesis
1) spermatogenesis = sperm
production (4 haploid cells)
- even distribution
Spermatogenesis
Gametogenesis (cont)
2) oogenesis = egg production
(1 haploid cell)
- uneven distribution (polar
bodies created)
Oogenesis
Comparing Mitosis and Meiosis
Mitosis
- Produces
genetically
identical cells
- Results in diploid
cells
- Takes place
throughout an
organism’s life
- Involved in asexual
reproduction
Meiosis
- Produces
genetically unique
cells
- Results in haploid
cells
- Takes place only at
certain time in life
cycle
- Involved in sexual
reproduction