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Chromosomal mutation
• A chromosomal mutation involves a change
in the structure or number of chromosomes
• 4 types of chromosomal mutations:
– Deletion: loss of all or part of a
chromosome
– Duplication: extra copy of all or part of a
chromosome
– Inversion: reverses the direction of parts
of a chromosome
– Translocation: part of one chromosome
breaks off and attaches to another
chromosome
Karyotype: A photomicrograph of
chromosomes arranged according to
a standard classification
What each of the human
chromosomes look like
In other words…
• Chromosomes are digitally arranged so
that they are matched with their
homologue or “partner” chromosome.
• Homologue chromosomes are the same
size, shape, and carry the same genes,
and one is inherited from each parent.
• They are numbered according to size.
Sex determination with karyotype
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The first 22 pairs are autosomes
Pair 23 are sex chromosmes—
XX = female
XY= male
Female and Male Karyotype
If there are chromosomal number
abnormalities, how do they form?
• Meiosis: the process of creating sperm or
egg from a diploid cell
• If there is a mistake when chromosomes
are separating, then the resulting sperm or
egg will have too many or too few
chromosomes.
Prophase I: homologous
chromosomes pairing into tetrads
Crossing over
• The chromosomes during prophase I
undergo crossing over, where parts of the
homologues randomly switch places.
Metaphase I: tetrads align, along
the metaphase plate
Anaphase I: homologous chromosomes
separate from the metaphase plate
• If chromosomes
do not properly
separate, this is
called
nondisjunction.
• Nondisjunction
leads to trisomy
and monosomy
disorders.
Telophase I: membranes form
around the separated homologues
Prophase II: spindle fibers bind to the
sister chromatids of each chromosome
Metaphase II: chromosomes align
along the metaphase plate
Anaphase II: sister chromatids
separate to opposite poles
Telophase II: nuclear membrane forms
around newly separated chromatids
• Note that each new nucleus formed has ½
the amount of DNA as the original cell.
• These cells are haploid cells.
Nondisjunction
• Other types of chromosomal
mutations alter the number of
chromosomes found in the cell.
• Nondisjunction: The failure of
homologous chromosomes or
sister chromatids to separate
during meiosis.
– Produces gametes that
have too many or too few
chromosomes
Normal
meiosis
Nondisjunction
Disorders due to Nondisjunction
• In humans, a zygote with 45 chromosomes
has only one copy of a particular
chromosome
monosomy
• In humans, a zygote with 47 chromosomes
has three copies of a particular
chromosome
trisomy