2. HOMOLOGOUS CHROMOSOMES
Homologous chromosomes are a
pair of chromosomes, one inherited
from each parent, that have
corresponding gene sequences; they
are similar but not identical (they
carry the same genes but possibly
different forms, or alleles, of those
genes).
Each member of the pair are called
homologues.
3. SOMATIC CELLS & PLOIDY
Somatic Cells (Body Cells) are cells
that are produced through mitosis
and make up most of a body’s
tissues and organs. These are not
passed on to children.
Somatic cells are diploid (2n),
containing 2 of each type of
chromosome in the nucleus at
interphase; hence homologous
pairs are present.
4. GAMETES & PLOIDY
Gametes (Sex Cells) are cells that are produced through
meiosis. Gametes are located in the reproductive organs
(ovaries & testes) and are passed on to children. The union
between the male (sperm) and female (ovum) gamete is
necessary in sexual reproduction to initiate the
development of a new individual.
Gametes are haploid (n) cells, containing a set of
chromosomes having only one member of each
chromosome pair present, thus homologous chromosome
pairs are not present.
5. Organism Haploid Number Diploid Number
Ameba 25 50
Chimpanzee 24
Earthworm 18
Fern 1010
Hamster 22
Honeybee 32
Human 23 46
Onion 16
CALCULATING HAPLOID/DIPLOID
6. MEIOSIS
Meiosis is the production of haploid cells (gametes) from a
diploid cell.
Ova – female gamete
Sperm – male gamete
Meiosis reduces the chromosome number such that each
daughter cell has only one of each kind of chromosome,
and is thus often referred to as reduction division.
The process of meiosis ensures that the next generation
will have:
the diploid number of chromosomes;
7. MEIOSIS
Meiosis resembles mitosis except that
it is actually two divisions not one;
these divisions are called Meiosis I and
Meiosis II.
Meiosis I results in haploid cells with
chromosomes made up of two
chromatids.
Meiosis II is essentially mitosis on
haploid cells.
The stages of meiosis resemble mitosis
10. GAMETE FORMATION
Formation of gametes occurs through a special form of cell
division in which the number of chromosomes is
reduced…Meiosis!
Two major types of gametes in most mammals:
Sperm
Male gamete that is relatively small in size and mobile.
Produced through a process of meiosis called
Spermatogenesis.
Ova/Ovum (egg)
Female gamete that is large in size and stationary, or
11. SPERMATOGENESIS
Spermatogenesis occurs in males
and produces four haploid
sperm cells per meiotic event.
Men are busy – meiosis
produces roughly 250,000,000
sperm per day.
12. OOGENESIS
Oogenesis occurs in females and
produces one haploid egg cell and three
polar bodies per meiotic event.
Polar bodies are small cells that contain
a nuclei and relatively little cytoplasm to
conserve nutrients for the secondary
oocyte or ovum. They are discarded and
eventually degenerate.
Woman are less busy in meiosis than
men – meiosis produces only a few
