Cellular Reproduction
Cell Reproduction
• What is cell reproduction?
• How many cells make up your body?
• How does the chromosome transmit
information from one generation to
another?
• DNA is a
molecule that
contains the
genetic code of
an organism.
• A GENE is a segment of DNA that
transmits information from parent to
offspring. A single molecule of DNA
has thousands of genes lines up end
to end.
• Like the strands of a sock…DNA coils
tightly before cell division. If it were
straight the DNA would be
approximately 5 cm long. (2 inches)
Gene
• When the cell is going to divide the
DNA coils up into a dense
chromosome structure.
Chromosome
• Cellular structure on which genes are
located.
• Pg. 212
• Chromosomes are
40% DNA and 60%
protein that supports
the DNA (histones).
• Scientists have
mapped the 100,000
genes that make up
the chromosomes of
humans.
A set of chromosomes
from a female
Chromosome structure
• Chromatids are
the two copies of
each
chromosome.
• Centromeres
are protein disks
that attach the
two chromatids.
• A karyotype is
the collection of
chromosomes
found in an
organisms
cells. Arranged
in order of size
and shape.
Karyotype Cont.
• It is a display of chromosomes of
a single cell. To obtain it, the cell
is stained, then a picture is taken
of it through a microscope just
before cell division, when the
chromosomes are easiest to see.
• Somatic cells contain 23
different chromosomes, but
contain two copies of each,
a total of 46 chromosomes.
All the cells in our body
other than gametes
• Homologous
chromosomes are the two
copies of each
chromosome type (for
example chromosomes 13
are homologous because
they are the same type.
Homologous Chromosomes &
Somatic Cells
Homologous Chromosomes
• Chromosomes that are similar in shape,
size, and the genes they carry.
They do
NOT have
the same
types of
DNA
sequence!
Allele
An alternate form of a gene
that is located at a specific
position on a specific
chromosome.
• A homologue is a
half set of
chromosomes. One
chromosome of a
pair.
• Diploid cells contain
two homologues. The
symbol for diploid is
2n. All somatic cells
are diploid. It
contains exactly two
copies of each
chromosome.
• Haploid cells
contain only one
homologue; if it
contains exactly
half of a species’
typical full set of
genetic material .
Only sex cells are
haploid (n).
• Gametes are sex cells and are haploid.
An organism’s reproductive cells, such as
sperm or egg cells
Draw the following table
Diploid
symbol Cells
# of homologues
2n
2 (46 chromosomes)
Somatic
23 pairs
haploid n
gametes
1 (23 chromosomes)
23 individual
chromosomes
A zygote is the fusion of a haploid sperm cell
and a haploid egg cell. A fertilized egg cell,
the first cell of a new individual.
Chromosome numbers of various organisms
Organism
Penicillium
Saccharomyces (yeast)
Mosquito
Housefly
Garden Pea
Corn
Adder’s tongue fern
Frog
Human
Orangutan
Dog
Number of Chromosomes
1-4
18
6
12
14
20
1,262
26
46
48
78
Adders Tongue Fern
Each Chromosome is
important to the
development of a
normal organism.
Monosomy is a
condition in which a
diploid cell is
missing a
chromosome. Most
embryos will not
survive if missing a
chromosome.
Down Syndrome:
Jared has a condition in
which his 21st
chromosome number is
three instead of
two.(trisomy 21 or
down syndrome). Pg 335
In Amniocentesis Amniotic
fluid is tested for
chromosome problems.
The normal frequency of
down syndrome is 1 in 1500.
For couples who are older
than 30 it is 1 in 1000. In
couples 35-40 it is 1 in 750.
In couples older than 45 the
risk is 1 in 16.
Alterations in chromosomes usually lead to
mutations. There are four types of alterations.
Mutations: alterations in chromosomes.
PG. 306
• Deletion is a process in which a chromosome
is damaged as fragments break off the
chromosome and are lost.
• Duplication occurs as fragments attach to the
homologous chromosomes.
• Inversion happens when fragments
of the original chromosome attach in
reverse order.
• Translocation occurs when a
fragment may join a non-homologous
chromosome.
Of the 23 pairs of chromosomes in human somatic
cells, 22 pairs are the same. These chromosomes are
called autosomes-not directly involved in determining
the sex.
The Sex Chromosomes, X,Y, determine the sex of the
organism. These chromosomes are called sex
chromosomes.
A combination of XX is a female.
A combination of XY is a male
Because an egg cell carries only the X chromosome
and the sperm cell carries either X or Y the sex of an
offspring is determined by the male sex cells.
Meiosis
• A form of cell division that
halves the number of
chromosomes when forming
specialized reproductive
cells, such as gametes or
spores.
• Results in four haploid cells
pg. 273
Review Link
Meiosis
Lab Partner Questions:
• Can meiosis be asexual?
• What phase is responsible for the
law of independent assortment?
• When will crossing over occur?
Crossing Over
• The exchange of reciprocal
segments of DNA by
chromosomes at the beginning
of meiosis
pg. 277
The separation of genes during
crossing over occurs more
frequently between genes that are
far apart on a chromosome than
for genes that are close together.
When these chromosomes segregate
in meiosis, they form gametes that
have completely new combinations of
alleles.
Meiosis review
Reviewing Information
Binary fission is a type of asexual reproduction
that produces identical offspring. (happens in
prokaryotic cells such as bacteria)
When Eukaryotic cells split the internal organelle
must also divide and the process is much more
complex. This process is known as the cell cycle.
Cell Cycle is a diagram of the growth and division of a cell.