Tai lieu tham khao Sinh học 12

XO Turner Syndrome
Features:
Female phenotype
Short stature
Webbing of the neck
Small, widely-spaced nipples
XXY Klinefelter Synd. Features:
Male
Often unusually tall; long arms and legs
Breast development
Underdeveloped testes
Hypophosphatemia: example of X-linked dominant inheritance
Symptoms: short stature, bow-legs, lowered phosphate levels in blood
males transmit trait to none of their sons and all of their daughters
females transmit trait similar to autosomal dominant
5 ft
45, X0 – Turner syndromes
http://www.gfmer.ch/Genetic_diseases/Turner_syndrome/Turner.htm
Total fetal
hydrops
normal intelligence;
may have 3D spatial problems
or math problems.
99% of cases
– aborted
1 in 2,500 or
1 in 2,000
liveborn females.
yalenewhavenhealth.org/.../ topic.asp?hwid=zm2596
Gynecomastia –
Male with female features
small testes,
inability to produce sperm
Mental retardation
is related directly to the number
of supernumerary X chromosomes
(-15 IQ unit per 1 extra X).
47, XXY – Klinefelter syndrome – or even 47, XXXY etc….
1 out of 500 or 1000 males;
most go through life undiagnosed
40% of embryos survive to birth
Cleft Palate...
In addition to needing plastic surgery to repair the opening, these children may have problems with their feeding and their teeth, their hearing, their speech, and their psychological development as they grow up.
Medical and technology advances have been invaluable in the treatment of the cleft lip and palate. Clefts occur 1 time in 1,000 births in Caucasians, more often in Asians and Native Americans, and less often in African Americans.
Fetal Alcohol Syndrome...
Fetal Alcohol Syndrome (FAS) and Fetal Alcohol Effects (FAE) are growing problems in the United States. Despite the warnings posted in bars and restaurants and the increased media attention given to the perils of alcohol use during pregnancy, the rate of drinking among women of childbearing age continues to rise. The incidence of FAS may be as high as 12,000 per year, with FAE evident in up to 36,000 infants per year. Drinking during pregnancy affects not only the mother, but also the growing fetus. Alcohol can cause physical deformities and neurobehavioral deficits in the infant and growing child. Thus, it is not surprising that FAS is the leading cause of mental retardation and the only one that is preventable.
ANY consumption of alcohol during ANY time during the gestation period can damage a baby’s brain.
For example, sickle-cell disease is caused by a mutation of a single base pair in the gene that codes for one of the polypeptides of hemoglobin.
A change in a single nucleotide from T to A in the DNA template leads to an abnormal protein.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
FISH analysis (Fluorescent in situ hybridization) -- translocation
mti-n.mti.uni-jena.de/~huwww/ MOL_ZYTO/imageAU9.JPG
FITC or Fluorescein (green),
Texas-red (red),
Rhodamine (red),
DAPI (blue)
COMMON FLUORO DYES
Green + RED = YELLOW
FISH analysis (Fluorescent in situ hybridization) --DELETION
http://lambertlab.uams.edu/images/cell.jpg
Two green, two reds
on different chromosomes
– no deletion
Two green, one red –
One red is deleted.
Interphase FISH, relaxed chromatin
Size of deletion can not be estimated.
Deletion size is smaller
than distance to green signal (probe)
GREEN SIGNAL SERVE AS A CONTROL PROBE
ON A SAME CHROMOSOME.
The First HapMap Success Story:
Age-Related Macular Degeneration
Two other risk variants have
been identified in the last two months.

Together these account for 74%
of risk, and point to powerful
new approaches to prevention
and treatment.
XY sex determination X-Y chromosomes
autosomes
SRY locus
Described in text, p. 283
All patients with same diagnosis
Grey: Normal responder.
Orange: Toxic responder. Blue: Non-responder.
Treat with conventional
drug or dose
Responders and patients
not predisposed to toxicity
All patients with same diagnosis
Treat with alternative
drug or dose
non-responders
and toxic responders
Evans, Johnson. Annu Rev Genomics Hum Genet 2001.
Dosage Compensation Mechanism for X-Linked Genes in Mammals

1. Gene dosage varies between the sexes in mammals, because females have two copies of X while males have one. Early in development, gene expression from the X chromosome must be equalized to avoid death. Different dosage compensation systems have evolved in different organisms.
2. In mammals, female somatic cell nuclei contain a Barr body (highly condensed chromatin) while male nuclei do not. The Lyon hypothesis explains the phenomenon:
a. Barr body is a condensed and (mostly) inactivated X chromosome. Lyonization of one chromosome leaves one transcriptionally active X, equalizing gene dose between the sexes.
b. An X is randomly chosen in each cell for inactivation early in development (in humans, day 16 postfertilization).
What is unusual about the following pedgree?
Males pass on the trait to all males: holandric, or Y-linked inheritance
Only males are affected
But affected males do not transmit trait to all sons
trait can be transmitted via females
An example of SEX-LIMITED trait: inherited as an autosomal dominant, but only one sex shows trait
Example: Precocious Puberty
Sex-Limited Traits
Fetal Alcohol Syndrome...
Facial characteristics that suggest the diagnosis of FAS.
The rarest form of spina bifida is when the spinal tissue actually protrudes from the body. This only occurs in 10% of all cases.
Spina Bifida...
Various degrees of leg and foot deformities are found in spina bifida patients, depending on the size of the improper spinal closure.
Hydrocephalus...
Normally within the brain there are some cavities named ventricles, where a liquid known as Cerebrospinal Fluid (CSF) is produced. The purpose of this is to protect the brain and spinal cord, acting as a shock absorber. It also carries away disposed materials. The CSF circulates from the ventricles towards a space that exists between the brain and the membranes (meninges) that surround it, from where it is "eliminated", into the blood stream.
In the individual with hydrocephalus, the fluid does not drain away properly, but accumulates.
In an infant, the seams of the skull have not yet fused, so the skull gets bigger as the fluid accumulates.
DNA Methylation and Cancer
Robertson KD. DNA methylation and human disease. Nat Rev Genet 2005
Dynamic Domains
Kosak ST. Gene Order and Dynamic Domains. Science 2004
Gleevec™ – Specifically Targets
An Abnormal Protein, Blocking
Its Ability To Cause Chronic Myeloid Leukemia
Multiple mutations lead to colon cancer
Genetic changes --> tumor changes
Cellular
Tumor Progression