Transcript X/X - Denton ISD

Genetic Disorders
Overview
• 6 billion base pairs of DNA
~ 3 meters of DNA
• Approximately 30,000 – 70,000 genes
* Approximately 80-100,000 proteins
• These genes are spread across 24 different
chromosomes
**One chromosome each from each parent, for a total of
23 pairs, or 46 chromosomes per cell**
• All normal human
cells (except sex
cells) have 46
chromosomes, half of
which are from mom,
and the other half are
from dad. (23 pairs of
homologous
chromosomes)
• 2 sets (46) of
homologous
chromosomes
=DIPLOID
• Pictures of chromosomes grouped in
order and in pairs = Karyotype
Karyotype Normal male
Chromosome
Number
Homologous
chromosomes
Diploid!
Dark bands
= Genes
Autosomal chromosomes
Sex
= non sex determining chromosomes, chromosomes
same shaped homologous
Sex chromosomes:
X/Y = male
X = female, Y = male
X/X = female
…still sex determination
Dad
• Probability of
having a boy or a
girl.
Mom
X
Y
X
XX
XY
X
XX
XY
X
Y
50% chance for boy
50% chance for girl
X
X
Girl Boy
Girl Boy
Chromosomal disorders
• What if you have extra chromosome?
• What if you are missing a chromosome?
Chromosomal disorders usually:
Increase chance of having disorders,
such as mental retardation, sterility, and
decrease life expectancy.
Is anything wrong?
Male
Chromosome 21 trisomy  Down syndrome
Trisomy 21( extra on the
21st)- Down Syndrome
• Redundant neck fold/flat
occipital (back of the head)
• Low set ears
• Protruding/large tongue
* Wide space between 1st & 2nd
toes
Trisomy 13 (47,XY,+13) –
Cleft Lip
Cleft Lip- a split or indentation in
the lip of a newborn baby.
Sex Chromosome Abnormalities
•
•
•
•
Turner syndrome
Klinefelter syndrome (XXY)
Triple X
XYY
Is anything wrong?
X
Turner’s syndrome
Turner Syndrome
• 45 Chromosomes , only one sex chromosome
• The incidence is about 1 in 5000 female births
but this is only the tip of the iceberg because
99% of Turner syndrome embryos are
spontaneously aborted.
• Individuals are very short, they are usually
infertile.
• Characteristic body shape changes include a
broad chest with widely spaced nipples and may
include a webbed neck.
• IQ and lifespan are unaffected.
Is anything wrong?
XXY
Klinefelter’s syndrome
• Klinefelter Syndrome 47,XXY
*The incidence at birth is about 1 in 1000 males.
*Testes are small and fail to produce normal levels of
testosterone which leads to breast growth in about 40% of
cases and to poorly developed secondary sexual
characteristics.
*Males are sterile.
*These males are taller and thinner than average and generally
have a slight reduction in IQ (10-15 points below sibs). Many
Kleinfelter males lead a normal life.
*Very rarely more extreme forms of Kleinfelter's syndrome occur
where the patient has 48, XXXY or even 49, XXXXY karyotype.
These individuals are generally severely handicap.
XXX Syndrome
XXX Syndrome
Triple X syndrome is not inherited, but usually
occurs as a random event during the formation of
the reproductive cells.
*There may be a growth spurt until the age of approximately eight years of age,
resulting in a taller than average final height
*They often have a increased risk of learning disabilities and delayed speech
and language skills.
*They have a slightly lower intelligence level than their siblings (the IQ may be
ten to fifteen points lower than their siblings).
*Females with this condition are not at any increased risk for medical problems.
XYY Syndrome
Men who have XYY's
syndrome are
substantially taller, tend
to be wiry-built, and tend
to have severe acne.
Minor birth defects -- like
pectus, crooked eye, and
minor outturning of the
elbows, are supposed to
be common in XYY's.
Color Blindness
Colorblindness
• 3 human genes
associated with color
vision are located on
the X chromosome.
• Because males have
one X chromosome, all
the genes will be
expressed, even if they
are recessive.