Practice Question
“Determining a karyotype is an important clinical method for
diagnosing genetic disorders. Explain why it is useful for
diagnosing monosomies and trisomies.”
(3 marks)
Key Ideas
• karyotype = photograph of all the chromosomes in a cell
• monosomy = one less chromosome; trisomy = one extra
• karyotype allows easy visual identification of changes in
chromosome number
Additional criteria
• Accuracy - Evidence of understanding, synthesis,
appropriate use of terminology
• Clear relationship between cause and effect
• Concise – Direct, to-the-point, no extra/unnecessary
information
To karyotype a set of chromosomes, a cell is
stained in order to see the distinction
between the bands and see the pattern
better. When karyotyping in order to diagnose
genetic abnormalities, you can tell through
size, shape and the number of
chromosomes, if there is an extra
chromosome (trisomy) or a missing
chromosome (monosomy). This is caused by
non-disjunction during meiosis.
What is a karyotype?
2.5 marks/3
For example, older pregnant women are more likely to have a child with Down
’s syndrome and they can have genetic testing done in order to see if their
child does have an abnormality. By knowing earlier, the parents can get
more information and prepare themselves. Once someone knows what they
are diagnosed with it allows them to get information and help them manage
the health problems that are related with the disorder.
A karyotype is a photograph of pairs of
homologous chromosomes (condensed) in a
cell, that is visible under a microscope; so
essentially you can see all the chromosomes
that exist in a person's cell. So when
diagnosing for a monosomy, the loss of a
chromosome, or a trisomy which is the gain
of an extra chromosome, then you can clearly
see whether a homologous pair has lost or
gained a chromosome through the karyotype.
3 marks/3
A karyotype is an image of pairs of homologous
chromosomes in a cell. Determining a karyotype is an
important clinical method for diagnosing genetic
disorders. Many of the genetic disorders that have been
identified are due an individual having an incorrect
number of chromosomes. Monosomy is a loss of
chromosome as a result of non-disjunction. Trisomy is
the gain of an extra chromosome as a result of nondisjunction. Even though there are no therapies that
directly threat or cure these disorders, medical
treatments help to manage the health problems that are
associated with the disorder; therefore karyotype is
important for diagnosing genetic disorders.
Explicit connection missing: karyotype  diagnosis?
2.5 marks/3
Monosomy is a loss of a chromosome due to nondisjunction, while a trisomy is the gain of an extra
chromosome due to non-disjunction. A karyotype is a
photograph of homologous chromosome pairs in a cell.
For a healthy individual, the karyotype will show 23 pairs
of chromosomes: each autosome must have two
chromosomes and there must be a pair of sex
chromosome. Therefore, when the karyotype is
arranged, the addition of absence of chromosomes
can be easily detectible, and based on the monosomy
or trisomy a genetic disorder can be identified. For
example, an extra copy of chromosome 21 will identify
Down Syndrome.
3 marks/3
For tomorrow…
pg. 198 #13
The process of meiosis is often called a
“reduction division”. Explain the use
of this term (3 marks).
Post response online.