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106 Cards in this Set

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the study of chromosomes and their abnormalities
cytogenetics
euploid
cell has normal amount of chromosomes (23 or multiple of 23)
polyploidy
presence of a complete set of extra chromosomes in a cell
aneuploidy
cells that do not contain a multiple of 23 chromosomes...extra or missing chromosomes
______ of the autosomes are among the most clinically important of the chrosomsome abnormalities.
aneuploidies
Is lacking a chromosome or having an extra chromosome more delitirious?
lacking a chromosome is more delitirious
chromosomes can be described by location of _______ which leads to different length arms.
centromere
metacentric chromosome
-centromere in middle
-arms equal in length
acrocentric chromosome
-centromere close to the tip
submetacentric chromosome
-centromere is neither at the tip nor in the center, it is somewhere in between
Can the centromere of a chromosome sit at the very tip of the chromosome?
no. the centromere will never be at the very tip.
T/F: Banding patterns are unique to each chromosome
true.
p arm
short (petite) chromosome arm
q arm
long chromosome arm ("comes after p)
13q13
chromosome 13, long arm, region 1, band 3
conventional nomenclature of naming loci
-to be more specific about location on chromosome
-R to L: general to specific
-chromosome #, arm, region, band
T/F: different staining techniques yield different banding patterns
true
Karytype Description of: normal female
46XX
Karyotype Description of: normal male
46Xy
Karyotype Description of: female with trisomy 21, Down Syndrome
47XX,+21
Types of Aneuploidies
1.Monosomy
2.Trisomy
Monosomy
-missing 1 chromosome
-homologous pair minus 1 = 1
-the presence of only 1 copy of a chromosome in an otherwise diploid cell
Trisomy
-1 extra chromosome
-homologous pair + 1 extra chromosome = 3
-three copies of a chromosome
Most common cause of aneuploidy
-nondisjunction
nondisjunction
-the failure of chromosomes to disjoin normally during meiosis I or II
-two chromosome homologs migrate to the same daughter cell instead of disjoining normally and migrating to different daughter cells.
-resulting gamete either lacks a chromosome or has two copies of it
-producing a monosomic or trisomic zygote, respectively
how does nondisjuction occur?
-mistake in dividing of chromosomes during meiosis
-made by spindle fibers
-2 chromosomes that should have been separated (1 sister chromatid to each pole) both go to same pole
-yields 1 daughter cell with 2 sister chromatids and 1 daughter cell with none
why does nondisjunction happen?
-appears to happen in women of advanced maternal age (in U.S. 35 years old)
-unsure as to why
Do most cases of nondisjunction occur in spermatogenesis or oogenesis?
-most occur in oogenesis
-some occur in spermatogenesis & mitosis but are rare
-nondisjunction is primarily a maternal meiotic error
translocation
-a peice of chromosome breaks off and attaches to another, usually non-related, chromosome
-also happens to advanced maternal age
-another way in which Down Syndrome occurs
would you be able to see a translocation on a karyotype?
-no
Trisomy Disorders
1. Trisomy 21 (Down Synd.)
2. Trisomy 18 (Edwards Synd.)
3. Trisomy 13 (Patau Synd.)
Of the trisomies, which is the only one that has a survival rate?
-down syndrome (trisomy 21)
Nondisjunction of sex chromosomes leads to which disorders?
1. Turner Syndrome
2. Klinefelter Syndrome
3. XXX
4. Xyy
Teratogen
agent that causes birth defects
Lysosomes
-small vesicles in cells filled with degrading enzymes
-these enzymes break down molecules into smaller constituents
Process of Lysosomal Action
-large molecule enters cell
-lysosome fuses with vesicle containing this large molecule
-molecule is broken down within this fused vesicle
-if lysosomes burst open, would attack cells
Lysosomal Failure
-lysosomes do not do job: do not break down larger molecules into smaller ones
-multi system deterioration: cardiovascular, joint, hearing/visual
Todipotent
-have potential to yield entire animal
-have access to all of genome
Examples of Trisomies
-Trisomy 21 (Down Syndrome)
-Trisomy 18 (Edward Syndrome)
-Trisomy 13 (Patau Syndrome)
Karyotype of male and female with Trisomy 21
-male: 47Xy21
-female: 47XX21
Presents with: palpebral fissures, flat maxillary region, short neck, hypotonia
Down Syndrome
Significant increased risk of: leukemia, congenital heart defects, GI obstructions
Down Syndrome
Presents with: elf features, SGA
Edward Syndrome
Presentation of hands: clenched fist with outside fingers overlapping middle
Edward Syndrome
T/F: Edward Syndrome is usually lethal in the 1st year.
True
T/F: Down Syndrome is usually lethal.
False
Serious heart malformations: VSD (ventricular septal defect)
Edward Syndrome
Presents with: cleft palate
Patau Syndrome
ASD (atrial septal defect), inguinal hernia, fare degree of MR in children who do survive
Patau Syndrome
Features: females, short, webbed neck, lack of secondary female sex characteristics
Turner Syndrome
Hormone Replacement Therapy early on can lead to ovulation and child bearing.
Turnder Syndrome
Often diagnosed at age when girl should have gotten period but did not.
Turner Syndrome
Karyotype for Klinefelter Syndrome
47XXy
2 X oocytes fertilized by 1 y sperm
Klinefelter Syndrome
Features: male, tall, disproportionately long limbs, gynecomastia, small testes, learning disabilities, sterile
Klinefelter Syndrome
small piece of distal end of X chromosome appears as though its falling off
Fragile X Syndrome
Fragile X Syndrome: boys or girls?
-affects boys more than girls but affects both
Features: long headed, large prominent ears, elongated face, mild-mod-severe MR
Fragile X Syndrome
one of the more common inherited forms of MR
Fragile X Syndrome
This gene yields a distorted product seen in Fragile X patients.
FMR1
Possible role of FMR1
-found shuttling between nucleus and cytoplasm
-perhaps moves transcript
Inheritance pattern: more frequently from moms to sons than from dads.
Fragile X Syndrome
Increased severity and frequency with subsequent generations.
Fragile X Syndrome
Severity of Fragile X Syndrome depends on how many _____ the patient has.
-tri-nucleotide repeats of CGG
5-50 TNRs
normal
>50-200 TNRs
premutation
>200 TNRs
affected
Pts. with PKU cannot break down _____.
phenylalanine
Pts. with PKU cannot have foods high in ____.
protein
Features: failure to thrive (developmentally delayed), liver problems, cataracts.
Classic Galactosemia
Tx: avoid dairy products
Classic Galactosemia
Features: craniofacial abnormalities, multisystem defects (cv, joint, hearing/visual)
Hurler Syndrome
Features: after period of fasting, pt. experiences lethargy, vomiting, build up of fatty acids
MCAD Deficiency
Tx:
-first: avoid fasting
-second: enzyme supplement
MCAD Deficiency
Often misdiagnosed as SIDs if death occurs early on
MCAD Deficiency
In cases where this dz is missed, it can be fatal in first 2 years of life.
MCAD Deficiency
Process of cell tissue movements whereby cells of blastula are rearranged so that they have new positions and neighbors.
Gastrulation
Process by which dorsal mesoderm and overlying ectoderm interact to form hollow neural tube.
Neurulation
Gives rise to entire embryo and then some
Inner Cell Mass
In absence of any female chromosomes during development, all you get is ____.
trophoblasts
In absence of any male chromosomes during development, all you get is _____.
ICMs
-outer cells in ball of cells that give rise to NONE of the embryo but rather to the placenta.
-does job of implanting in endometrial lining
trophoblast
Trophoblast separates into two kinds of cells:
1. Syncytiotrophoblast
2. Cytotrophoblast
whole bunch of nuclei under one big membrane within cytoplasm
syncytiotrophoblast
-formed by cytotrophoblast
-site across which diffusion occurs between fetus and mother
Chorion
single layer of cells formed from a flatted out ICM
epiblast
epiblast gives rise to ____.
all tissues of the body
How does the amnion form?
cells at edges of epiblast start to proliferate and grow upwards forming a dome.
3 germ layers formed by the epiblast.
1. ectoderm
2. mesoederm
3. endoderm
what happens soon after the 3 germ layers form?
they roll up into a tube within a tube within a tube (like paper)
ectoderm gives rise to:
skin, hair, nails
mesoderm gives rise to:
deep to skin but not within gut (muscle, bone, entire CV system)
endoderm gives rise to:
lining of gut tube from oral to anal cavity
when is the term embryo used?
1st 8 weeks
when is the term fetus used?
after the first 8 weeks.
rod of mesodermal cells that runs long axis of embryo
notocord
what happens in presence of notocord?
brain and spinal cord development
what happens in absence of notocord?
development stops
what happens in the presence of an extra notocord?
2 embryos develop
special subset of ectoderm lying just above notocord that is influenced by instructions from notocord to become special ectoderm
neurectoderm
roles up into its own tube to form brain and spinal cord
neurectoderm
pile of ectodermal cells at very top of limb bud
AER (apical ectodermal ridge)
ZPA is found in the ____.
mesoderm
ZPA regulates:
-outgrowth of limb and polarity of how digits form
What happens if ZPA is removed?
-AER goes away
-limb development stops
6 digits in a pattern of 4,3,2-2,3,4 (mirror image) form.
when another ZPA is added 180 degrees away from original ZPA