Transcript Gene Disorders


Gene disorder refers to the harmful effect a
detrimental allele produces when it occurs at
a significant frequency in a population.
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Most disorders are rare because affected
individuals often die at a relatively young age, or
cannot reproduce.
Not all defects are recessive.
For example, Huntingtons disease is
autosomal dominant.
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Human somatic cells normally have 23 pairs
of chromosomes.
divided into seven groups characterized by size
and shape
 22 pairs of autosomes
 1 pair of sex chromosomes
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 XX = Female
 XY = Male
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Failure of chromosomes to separate correctly
during meiosis I or II is called primary
nondisjunction.
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Down Syndrome caused by trisomy 21
 1 in 1700 for mothers < 20.
 1 in 1400 for mothers >20<30.
 1 in 750 for mothers >30<35.
 1 in 16 for mothers >45.
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Down Syndrome
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Chromosome 21 does not
separate correctly.
They have 47
chromosomes in stead of
46.
Children with Down
Syndrome develop
slower, may have heart
and stomach illnesses
and vary greatly in their
intelligence.
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X Chromosome
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XXX or XXY yields Klinefelter syndrome
XO yields Turner syndrome
Y Chromosome
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XYY - Jacob syndrome
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Klinefelter’s
Syndrome
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XXY, XXYY, XXXY
Male
Sterility
Small testicles
Breast enlargement
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Turner’s
Syndrome
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X
Female
sex organs don't
mature at adolescence
sterility
short stature
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XYY Syndrome or Jacob Syndrome
Normal male traits
 Often tall and thin
 Associated with antisocial and behavioral problems
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Sickle-cell anemia is a recessive inherited
disorder in which afflicted individuals have
defective hemoglobin, and thus are unable to
properly transport oxygen to tissues.
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Homozygotes have sickle-cell.
Heterozygotes usually appear normal, but are
resistant to malaria.
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Cri-du-chat
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Deletion of material on
5th chromosome
Characterized by the
cat-like cry made by cridu-chat babies
Varied levels of mental
handicaps
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Genetic counseling identifies parents at risk
of producing children with genetic defects
and assesses the state of early embryos.
High-risk pregnancies
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couples with recessive alleles
mothers older than 35
 amniocentesis
 chorionic villi sampling
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Counselors can look for three things in cell
cultures in search of genetic disorders:
aneuploidy or gross alterations
 proper enzyme functioning
 association with known genetic markers
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Mutations are accidental changes in genes.
•rare, random, and usually result in
recessive alleles
•pedigrees are used to study heredity
•
Family pedigrees
–
Chart of family’s history
• Key
–Males-squares, females-circles
–Shaded means individual is affected by
disorder
–Line between square and circle indicates a
union
–Vertical line downward indicates child
»Multiple children are drawn off a horizontal
line
•
Pedigrees for autosomal disorders
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An affected child from 2 unaffected parents indicates
an autosomal recessive trait
• Counselor can suggest genetic testing
–
Two affected parents produce an unaffected child
• Indicates both parents are heterozygous for
an autosomal dominant trait
• Another indicator- when both parents are
unaffected, none of their children are either
–
Study the two pedigrees on the following slides
To make a karyotype -
Arrange chromosomes in
matching pairs from largest
to smallest.
Gel from gel electrophoresis
Inherited condition where blood is slow to clot or does
not clot at all
 only expressed when individual has no
copies of the normal allele
 Royal hemophilia - sex-linked
•
Pedigrees for sex-linked disorders
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X-linked disorders
• X-linked recessive disorders
–To be affected, daughters must inherit it from both
parents
–Sons can only inherit it from mother, therefore more
males affected than females
• X-linked dominant disorders
–Affected males pass the trait only to daughters
–Females can pass trait to both daughters and sons
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Y-linked disorders
• Present only in males
• Fathers pass trait to all sons
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Study the pedigree on the following slide
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The human genome project
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Goals
 To construct a base sequence map
 To construct a genetic map of each chromosome
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The base sequence map
 Humans share many genes in common with all
other living organisms
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The genetic map
 Researchers only need to know a short
sequence of bases in a gene, and a computer
searches the genome for a match
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Is it right to use
cloning to create an
entirely new
human being?
Is it ethical to
create an
embryonic copy of
John Doe to supply
cells to keep John
alive?
Does a
multicellular ball of
tissue -- an embryo
-- have the same
rights and status as
a human being?