BIO NOTES - Translocation & Chromosomes
When chromosomes 2 and 20 exchange segments, (b) Alagille syndrome, with
distinctive body features, sometimes results because of organ malfunction caused by
the chromosome 20 translocation.
● The translocation is now unbalanced, with extra material from one chromosome
and missing material from another chromosome.
● Embryos with unbalanced translocations usually result in miscarriage, but those
individuals who are born often have severe symptoms.
● Some Down syndrome cases are caused by an unbalanced translocation
between chromosomes 21 and 14.
○ In other words, because a portion of chromosome 21 is now attached to a
portion of chromosome 14, the individual has three copies of the genes
that bring about Down syndrome when they are present in triplet copy. In
these cases, Down syndrome is not caused by nondisjunction during
meiosis but is passed on normally, as is any other genetic trait.
● Human Syndromes
○ Changes in chromosome structure occur in humans and lead to various
syndromes, many of which are just now being discovered.
○ Sometimes changes in chromosome structure can be detected in humans
by doing a karyotype.
○ They may also be discovered by studying the inheritance pattern of a
disorder in a particular family.
● Deletion Syndromes.
○ Williams syndrome occurs when chromosome 7 loses a tiny end piece
○ Children who have this syndrome look like pixies, with turned-up noses,
wide mouths, a small chin, and large ears.
○ Although their academic skills are poor, they exhibit excellent verbal and
musical abilities.
○ The gene that governs the production of the protein elastin is missing, and
this affects the health of the cardiovascular system and causes their skin
, to age prematurely. Such individuals are very friendly but need an ordered
life, perhaps because of the loss of a gene for a protein that is normally
active in the brain.
■ Cri du chat (“cat’s cry”) syndrome is seen when chromosome 5 is
missing an end piece. The affected individual has a small head, an
intellectual disability, and facial abnormalities.
■ Abnormal development of the glottis and larynx results in the most
characteristic symptom—the infant’s cry resembles that of a cat.
● Translocation Syndromes.
○ A person who has both of the chromosomes involved in a translocation
has the normal amount of genetic material and is healthy, unless the
chromosome exchange breaks an allele into two pieces.
○ The person who inherits only one of the translocated chromosomes no
doubt has only one copy of certain alleles and three copies of certain other
alleles.
○ A genetic counselor begins to suspect a translocation has occurred when
spontaneous abortions are commonplace and family members suffer from
various syndromes.
○ A microscopic technique allows a technician to determine if a
translocation has occurred.
○ Although they have the normal amount of genetic material, the
rearrangment of the genetic material also commonly causes phenotypic
and physi.ological problems, collectively called Alagille syndrome.
■ People with this syndrome ordinarily have a deletion on
chromosome 20 , which can lead to a congenital heart condition
called tetralogy of fallot, which produces digital clubbing of the
fingers. Liver problems are also common in Alagille syndrome. The
symptoms of Alagille syndrome range from mild to severe, so some
people may not be aware they have the syndrome until after
they’ve had children.
● Translocations can also be responsible for a variety of other disorders, including
When chromosomes 2 and 20 exchange segments, (b) Alagille syndrome, with
distinctive body features, sometimes results because of organ malfunction caused by
the chromosome 20 translocation.
● The translocation is now unbalanced, with extra material from one chromosome
and missing material from another chromosome.
● Embryos with unbalanced translocations usually result in miscarriage, but those
individuals who are born often have severe symptoms.
● Some Down syndrome cases are caused by an unbalanced translocation
between chromosomes 21 and 14.
○ In other words, because a portion of chromosome 21 is now attached to a
portion of chromosome 14, the individual has three copies of the genes
that bring about Down syndrome when they are present in triplet copy. In
these cases, Down syndrome is not caused by nondisjunction during
meiosis but is passed on normally, as is any other genetic trait.
● Human Syndromes
○ Changes in chromosome structure occur in humans and lead to various
syndromes, many of which are just now being discovered.
○ Sometimes changes in chromosome structure can be detected in humans
by doing a karyotype.
○ They may also be discovered by studying the inheritance pattern of a
disorder in a particular family.
● Deletion Syndromes.
○ Williams syndrome occurs when chromosome 7 loses a tiny end piece
○ Children who have this syndrome look like pixies, with turned-up noses,
wide mouths, a small chin, and large ears.
○ Although their academic skills are poor, they exhibit excellent verbal and
musical abilities.
○ The gene that governs the production of the protein elastin is missing, and
this affects the health of the cardiovascular system and causes their skin
, to age prematurely. Such individuals are very friendly but need an ordered
life, perhaps because of the loss of a gene for a protein that is normally
active in the brain.
■ Cri du chat (“cat’s cry”) syndrome is seen when chromosome 5 is
missing an end piece. The affected individual has a small head, an
intellectual disability, and facial abnormalities.
■ Abnormal development of the glottis and larynx results in the most
characteristic symptom—the infant’s cry resembles that of a cat.
● Translocation Syndromes.
○ A person who has both of the chromosomes involved in a translocation
has the normal amount of genetic material and is healthy, unless the
chromosome exchange breaks an allele into two pieces.
○ The person who inherits only one of the translocated chromosomes no
doubt has only one copy of certain alleles and three copies of certain other
alleles.
○ A genetic counselor begins to suspect a translocation has occurred when
spontaneous abortions are commonplace and family members suffer from
various syndromes.
○ A microscopic technique allows a technician to determine if a
translocation has occurred.
○ Although they have the normal amount of genetic material, the
rearrangment of the genetic material also commonly causes phenotypic
and physi.ological problems, collectively called Alagille syndrome.
■ People with this syndrome ordinarily have a deletion on
chromosome 20 , which can lead to a congenital heart condition
called tetralogy of fallot, which produces digital clubbing of the
fingers. Liver problems are also common in Alagille syndrome. The
symptoms of Alagille syndrome range from mild to severe, so some
people may not be aware they have the syndrome until after
they’ve had children.
● Translocations can also be responsible for a variety of other disorders, including
