Autosomal & Chromosomal Disorders

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Transcript Autosomal & Chromosomal Disorders

Autosomal & Chromosomal Disorders
Human Genetic Disorders
 There are many genetic disorders that
plague humans.
 Some disorders are caused by a change
in just one allele in a gene while others are
much more complicated.
 It is the hope of many scientists that one
day, we will have the advanced technology
to isolate the defective genes that cause
these disorders and completely remove
them from the human genome.
Autosomal Disorders
 Autosomal disorders involve
dominant, recessive, or other
types of traits that can produce
multiple abnormalities.
 These traits are found on
chromosomes 1-22.
 Cystic Fibrosis, Sickle Cell, and
Huntington’s disease are just a
few examples of autosomal
Cystic Fibrosis (CF)
 Is caused by a recessive allele in chromosome
 Most cases of CF involve a gene missing 3
bases in the middle of a sequence for a protein.
 Because of the faulty protein, cells can not
transport chloride ions across their membranes.
 Children with CF have serious digestive
problems as well as producing a thick mucus
that clogs lungs & breathing passageways.
Sickle Cell Disease
 Is caused by an incomplete/co-dominant gene on
chromosome #11.
The sickle cell gene has just one DNA base different
from the normal one.
As a result, abnormal hemoglobin is formed which can
“sickle” under low levels of oxygen.
These sickled cells are rigid & tend to get stuck in
capillaries which can damage cells, tissues & organs.
In some cases it can be fatal.
Individuals with both recessive genes are said to have
sickle-cell disease. Those who are heterozygous for
the trait are said to have sickle-cell trait.
Inheritance of
Sickle-cell Disease
Incomplete Dominance
Huntington’s Disease (HD)
 Is caused by a dominant gene on
chromosome #4
 Individuals with HD have a slightly larger
huntingtin gene than usual. By middleage, these abnormal proteins then begin
to attack brain cells.
 Affected people are irritable, depressed,
lose muscle control & eventually die.
Huntington’s Disease
Other Autosomal Disorders
 Recessive:
 Albinism (lacking skin pigment melanin)
 Phenylketonuria (PKU- can’t break done phenylalanine causing
problems with brain development)
 Tay-Sachs (fatty acids accumulate in the nerve cells of the brain;
usually fatal)
 Dominant:
 Achondroplasia (dwarfism)
 Hypertrichosis (werewolf syndrome)
Chromosomal Disorders
 Chromosomal disorders
occur when homologous
chromosomes fail to
separate (nondisjunction)
during meiosis.
 This creates a genome with
either an EXTRA
chromosome or a MISSING
 Nondisjunction can occur
with any chromosome (123).
 Downs, Turner’s, and
Klinefelter's syndromes are
just a few examples of
chromosomal disorders.
Downs Syndrome (DS)
 Is caused by an extra of chromosome #21.
 Most cases of DS are trisomy 21, however there are
other types of DS (Mosaic and Translocation) .
 Often DS is associated with some impairment of
cognitive ability and physical growth as well as facial
 The incidence of Down syndrome is estimated at 1 per
800 to 1,000 births, although these statistics are heavily
influenced by the age of the mother.
 Down syndrome is not generally an inherited disorder,
(Translocation DS may be an exception).
Turner Syndrome
 Is caused by a missing X chromosome,
monosomy X, in females (XO).
 In rarer cases a second X chromosome is
present but abnormal, while others with the
condition have some cells with a second X and
other cells without it (mosaicism).
 In Turner syndrome, female sexual
characteristics are present but generally
 Is caused by an extra X chromosome in
males (XXY).
 The principal effects are development of
small testicles and reduced fertility.
XYY or Super-male Syndrome
 The XYY syndrome is a disorder in which a male infant is
born with an extra Y chromosome.
Boys with XYY syndrome tend to be tall and have
difficulties with language. The IQ tends to be slightly lower
than that of other family members.
Most XYY males have normal testosterone levels, sexual
development and usually have normal fertility.
The XYY syndrome was once thought to cause aggressive
or violent criminal behavior, but this theory has been
Some medical geneticists question whether the term
"syndrome" is appropriate for this condition because its
phenotype is normal and the vast majority of 47,XYY males
don’t know their karyotype.