CONNECT!
•What are these things?
•Why are they called “mutants”?
•What is a mutation?
B. MUTATIONS
• changes in the genetic
material
• If these mutations occur in sex
cells, they may be transmitted
to the next generation
• Mutations occurring in body
cells may be perpetuated in
the individual, but will NOT be
passed on to offspring
2 Types of Mutations
1. Chromosome
2. Gene
Chromosomal Alterations
(mutations)
are changes in the number of chromosomes or
in the structure of chromosomes
• The effects of chromosomal changes are often
visible in an organism because many genes are
involved.
Chunk!
• Define mutation.
• Mutations in certain kinds of cells will be passed
on to offspring. What are these cells?
• Mutations in these cells are NOT passed on to
offspring. What are these cells?
• Name two types of mutations.
• What is a chromosomal alteration?
• Why are chromosomal alterations often visible?
THINK!
• Do eggs and sperm have the same number of
chromosomes as a regular body cell?
• Why/why not?
Body Cells
• Body cells have the full amount of
chromosomes for the species. This is
called the diploid (2n) number. The n
refers to the # of different chromosomes,
while the 2 indicates that there are 2
homologous chromosomes of each #.
• For example, human body cells have a
diploid number of 46 chromosomes. This
means that each body cell has 23 pairs of
homologous chromosomes.
Diagram of Human Diploid Number
Why is this diploid? What kinds of cells are diploid?
Human Karyotype
Chromosome
Number
• Meiosis is a special cell division that occurs in
the gonads of sexually reproducing organisms to
produce gametes (sex cells or sperm and egg).
• Meiosis cuts the number of chromosomes in
half, so it is referred to as reduction division.
• The gametes are haploid (half the normal
chromosome number of body cells).
Meiosis produces variation in
gametes
GONADS
MAKE
HAPLOID
GAMETES
BY
MEIOSIS
What is the function of gametes?
• Sperm and egg join in the process of
fertilization to form a zygote, which
restores the species chromosome
number for body cells.
Reproduction
•How many
chromosomes in the
mother cell at far
right?
•How many
chromosomes are in
the father cell at far
right?
•How many
chromosomes are in
the egg and sperm
cell at far right?
•Why are body cells
called diploid?
•Why are sperm and
eggs called haploid?
•What restores the
diploid number of
chromosomes?
DISJUNCTION
• If there is a junction
between two ATV trails,
what does that mean?
• So, disjunction means…?
• Normally during meiosis,
homologous chromosomes
separate from each other;
this separation is known as
disjunction
• Sometimes, a pair of homologous chromosomes
fails to separate from each other, which results
in gametes with more or less than the normal
chromosome number; when chromosomes do
not separate, it is called nondisjunction.
Chunk!
• How many chromosomes are in the cell on the left?
• This is the normal # for this species. What is the term for the normal
# of chromosomes in a body cell?
• What mistake occurred in the middle cell?
• The gametes should all be haploid, which means a chromosome #
of ___ for this species.
• How many of the gametes have the proper # of chromosomes?
• What is this type of mistake called?
• If gametes from
nondisjunction are
involved in fertilization,
the resulting zygote may
have more or less than
the normal 2n
chromosome number.
• For example, in humans,
Down’s Syndrome
usually results from
possessing an extra 21st
chromosome. This is
caused by
nondisjunction of
chromosome # 21
during meiosis in one of
the parents.
More examples of Nondisjunction
Changes in Chromosome Structure
• This occurs when chromosomes randomly break
and re-attach
Navel orange
The mutation causes the orange to develop a second orange at the base of the original fruit, opposite the
stem, as a conjoined twin in a set of smaller segments embedded within the peel of the larger
orange. From the outside, it looks similar to the human navel, thus its name.
Because the mutation left the fruit seedless, and therefore sterile, the only means available to cultivate
more of this new variety is to graft cuttings onto other varieties of citrus tree. Two such cuttings of the
original tree were transplanted to California in 1870, which eventually led to worldwide popularity.
Today, navel oranges continue to be produced via cutting and grafting. This does not allow for the usual
selective breeding methodologies, and so not only do the navel oranges of today have exactly the
same genetic makeup as the original tree, and are therefore clones, in a sense, all navel oranges
can be considered to be the fruit of that single over-a-century-old tree.
Chunk!
• If gametes from nondisjunction are involved in fertilization,
what is the result?
•Give an example in humans.
•What are some types of changes in chromosome structure?
JFF!