A closer look at
chromosomes . . .
Chromosomes contain our genetic
material and are our ‘blue print’ for
making ourselves.
Chromosomes contain our DNA
(deoxyribonucleic acid)
Each of our chromosome contains
different genetic information about
us
Hair Colour
Size of Nose
Freckles?
How many toes
do I have?
Tongue Roll
Curly Hair
You receive one chromosome from
your mother and one from your
father. Therefore you have TWO
sets of information for each trait.
Chroma . . . what?
Chromatin: Uncondensed
genetic material present in
the nucleus during
interphase.
Chroma . . . what?
Chromosome: Condensed
form of genetic material
You have 46
chromosomes
Chroma . . . what?
Chromosome:
Condensed form of
genetic material
You have 46
chromosomes
Chroma . . . what?
Chromatids: Single strand
that makes up a
chromosome (not a
homologous chromosome)
Sister chromatids are
identical
Mistakes In Meiosis
Mistakes in
Separation
Aneuploidy:
Error during meiosis
Separation of chromosomes
doesn’t take place properly
resulting in cells have too many or
too few chromosomes
Mistakes in
Separation
Caused by: NONDISJUNCTION
Failure of homologous
chromosomes to separate in
meiosis I
Failure of sister chromatids to
separate in meiosis II
Types of Aneuploidy
MONOSOMY:
Sex cell missing one
chromosome (in
place of a
homologous pair)
Example
Example of a
monosomy:
Turner’s
Syndrome, born
only with an X
Types of Aneuploidy
POLYSOMY:
Condition where there are
more chromosomes than
required (in place of a
homologous pair)
Example
Example of trisomy
Down Syndrome
is a trisomy of the
21st chromosome
Types of Aneuploidy
POLYPLOIDY:
Non-disjunction of all of the
chromosomes in a gamete that
unites with a haploid gamete to
produce 3 sets of chromosomes
(3n)
NONDISJUNCTION
Crossing Over
Mistakes in Crossing
Over
Pieces of genetic information are
exchanged but do not reattach
properly
Examples of
Crossing Over
Mistakes
Deletion:
When exchanged information does
not reattach to the chromosome
Example
Example of
deletion:
Cru du chat is a
deletion of the
fifth chromosome
Examples of
Crossing Over
Mistakes
Inversion:
Segment of DNA reattaches to
chromosome but in the reverse
order
Examples of
Crossing Over
Mistakes
Duplication:
The exchanged information is
repeated on the chromosome
Examples of
Crossing Over
Mistakes
Example of
deletion:
Charcot-MarieTooth Disease is a
duplication of a
portion of
chromosome 17
Examples of
Crossing Over
Mistakes
Translocation:
Movement of information from one
chromosome to a non-homologous
chromosome