chromosomes Flashcards
it is the study of chromosomes variations and their effects on phenotypes
cytogenetics
it is stains darkly and harbors dna repeats
heterochromatin
it is light staining and contains protein-encoding genes
euchromatin
chromosomes consists of
(needed for cell division)
dna and proteins w a small amt of RNA
the essential par:
- telomeres
- centromeres
- origin of replication sites
centromeres include
dna repeats and protein that enable the cell to divide
171dna base pair
*protein is the centromere protein A
- cover half a million dna base pair
- when replicated, sister chromatids separates at anaphase and each retains some CENP-A, passed to next generation, NOT dna (epigenetic change)
it have telomere-like repeats that gradually change inward toward the centromere, as protein-encoding genes predominates
subtelomeres
how are chromosomes distinguishable
size
centromere position
satellites
staining patterns
*they are imaged and displayed in charts called karyotypes
centromere that has two fairly equal arms
metacentric
centromere has long arm and a short arm
submetacentric
centromere is near a tip, so that it has one long arm and one very short arm
acrocentric
- it pinches off only a small amt of material toward one end
these are older techniques that culture chromosomes from fetal cells in the amniotic fluid or chorionic villi, respectively
amniocentesis:
- needle pass through the abdominal wall, removes a small sample of amniotic fluid from the uterus
- fetal cells in the fluid are cultured for 7 to 10 days then 20 cells are karyotyped
- performed after 14 weeks of pregnancy, limit to age over 35 (bcs the risk of miscarriage rises with maternal age)
chorionic villus sampling (CVS):
- cells sampled btwn week 10 and 12 , come from the chorionic villi, which are fingerlike structures that developed into the placenta
- risk:
rare mutation can occur that lead to misleading results
(If the test shows an abnormal chromosome in the villus cells that isn’t actually in the fetus, parents might choose to terminate a healthy pregnancy.
Conversely, if the villus cells look normal but the fetus has chromosomal issues, parents might believe everything is fine when it isn’t.)
- limitations:
cannot detect biochemical disorders bcs it doesnt sample amniotic fluid
this is less discriminating than the other
staining chromosomes is less discriminating than FISH, fluorescence in situ hybridization
FISH:
- ability to tell chromosomes apart by banding patterns
- adds more precision by using dna probes that attach to chromosomes segments = produce a flash of color
- goal: create a clear, detailed pic of chromosomes t detect any potential genetic abnormalities (extra chromosome 13, 18 or 21 and sex chromosomes anomalies)
display chromosome bands -
show chromosome parts -
display chromosome bands - ideograms
show chromosome parts - digital karyotypes
this detects overrepresentation of dna pieces from extra chromosomes
cell-free fetal dna analysis
- done at 10 weeks or later
- rapidly replacing the older techniques
it has 22 pairs of autosomes and one pair of sex chromosomes
euploid
“good set”
it have extra chromosomes setS
polyploid
it have a missing or extra chromosomes
aneuploids
“not good set”
- trisomies (extra C), less harmful
- momnosomies (absence of C)
= spontaneously aborted
which is more harmful?
trisomies vs monosomies
sex C aneuploidy vs autsomoal aneuploidy
monosomies
sex C aneuploidy
uneven distribution of chromosomes in meiosis
nondisjunction
- causes aneuploidy
- most autosomal aneuploids ceases developing as embryos
it result from crossing over after pairing errors in synapsis or an in an inversion heterozygote
deletions and duplications
- microdeletions and microduplications may explain many diseases
the short arm of 2 acrocentric chromosomes break, leaving sticky ends on the long arms that join to form an unusual, large chromosomes with 2 long arms
Robertsonian translocation
two nonhomologous chromosomes exchange parts
reciprocal translocation
places a dna sequence from one C into a nonhomologous chromosomes
insertional translocation
it may have an associated phenotype and produces some unbalanced gametes
translocation carrier
which inversion includes the centromere
paracentric inversion - does not include centromere
pericentric inversion - does include centromere within the loop
this shatters chromosomes
chromothripsis
it repeat one C arm but delete the other. they form when the centromere divides in the wrong place in meiosis
isochromosomes
- meiotic error, unbalanced genetic material
- a chromosomes that has identical arms
- known for chromosomes 12 and 21 for the long arms of the X and the Y
it is the 2 copies of a C or part of one are inherited from one parent, and not from the other
uniparental disomy (UPD)
result from a
- nondisjunction in both gametes
- form a trisomic cell that loses a chromosome
euploid:
aneuploid:
polyploid:
euploid: normal no. of C sets (46)
aneuploid: missing or extra C45 or 47)
polyploid: extra full set of chromosomes (69)
similarities and differences btwn Amniocentesis vs. CVS
Alike:
Both test fetal genetic material for abnormalities.
Different:
Amniocentesis is done later in pregnancy (15–20 weeks) and uses amniotic fluid.
CVS is done earlier (10–13 weeks) and samples placental tissue.
A diagram showing a chromosome’s structure, banding patterns, and relative size.
ideogram
47, XXX:
45, X:
47, XX:
48, XXYY:
a. 47,XXX: Female, usually healthy but may have mild learning delays.
b. 45,X (Turner syndrome): Female, short stature, infertility.
c. 47,XX, trisomy 21: Female with Down syndrome.
d. 48,XXYY: Male, possible learning disabilities and physical differences.
Triploid vs. trisomic cells
Triploid: Three full sets of chromosomes (69 total).
- 2/3 of triploids result from fertilization of an ooocyte by two sperms
- 1/3 of triploid, forms diploid gamete
Trisomic: One extra chromosome (e.g., 47 chromosomes).
what are the Edwards syndrom types
trisomy 18
mosaic trisomy 18
translocation
what arethe atypcal chromosomes causing duplication/ deletions
ring chromosomes
isochromosomes
translocation chromosomes
what are the 3 types of translocations
Reciprocal: Two chromosomes exchange pieces.
Robertsonian: Two acrocentric chromosomes join at the centromere.
Unbalanced: Pieces are lost or gained, causing genetic problems.
Gene sequence in an isochromosome
One chromosome arm is missing, and the other is duplicated.
Ring chromosome formation:
Ends of a chromosome (telomeres) break off and fuse, forming a circle.
*genes can be lost or disrupted = symptoms
it is the largest constriction of a chromosome
centromere
- it is where the spindle fibers attach when the cell divides
- consists of dna ans proteins
when do certain centromere-associated proteins synthesied
only when mitosis is imminent
forming a structure called a kinetochore that contacts spindle fibers, enabling the cell to divide
where does centromeres replicate towards
the end of S phase of the cell cycle
* a protein that may control the process is centromere protein A or CENP-A
When the replicated (sister) chromatids separate at anaphase, each member of the pair retains some CENP-A. The protein therefore passes to the next cell generation, but it is not DNA.
epigenetic change
two tiniest chromosomes are
chromosomes 21:
chromosomes 22:
* which is why they are out of place in karyotypes
chromosomes 21:
- gene “desert”
- harboring a million base stretch w no protein encoding genes at all
- out of place in karyotypes
- 225 genese
chromosomes 22:
- “gene jungle”
- 545 genes
karyotype with one extra chromosomes
trisomy
- a chromosome number other than 46 have an extra chromosome
these are the 5 human chromosomes have boblike ends, that extend from a thin , stalk like bridge
satellites
(13,14,15,21,22)
stalk regions:
- do not stain
- carry many copies of gene encoding ribosomal RNA & ribosomal proteins
- these areas coalesce to form the nucleolus
what are the risk of aminocentesis
risk of miscarriage, which rise with maternal age
this adds precision by applying pieces of DNA, called probes, which are attached to molecules that produce a flash of color when they bind their complements on the chromosomes in a tissue sample.
fluorescence in situ hybridization
one C absent -
one extra C -
part of C missing -
part of C present twice -
one C absent - monosomy
one extra C - trisomy
part of C missing - deletion
part of C present twice - duplication
Two chromosomes join long arms or exchange parts -
Segment of chromosome reversed -
A chromosome with identical arms -
translocation
inversions
isochromosomes
the meiotic error that causes aneuploidy
nondisjunction
- a chromosome pairs does not separate at anaphase of either 1st or 2nd meiotic division
= unequal division produces a sperm or oocytes that has 2 copies of a particular chromosomes or non, rather than one copy
what is the sequence for each telomere
TTAGGG
- in most cell types, telomeres shortens with mitotic cell division
a karyotype with one extra chromosome
trisomy
this displays chromosomes in pairs by size and by physical landmarks that appear during mitotic metaphase, when dna coils tightly, enabling it to be visualized
karyotype
* can reveal certain conditions that dna sequencing can miss (visual display of chromosomes used to detect abnormalities)
- karyotype of indiv from diff populations can reveal the effects of environmental toxins, if abnormalities appear only in grp exposed to a contaminant. bcs chemicals and radiation often break chromosomes into fragments or rings, detecting this genetic damage
how many human chromosomes type
24
large being (1) while smallest (22), the other 2 chromosomes are the X and Y
chromosomes that have only one arm but humans do not
telocentric chromosomes
long arm - q
short arm - p
it is used to place the needle and to visualize the fetus
ultrasound
- helps ensure the needle is placed safely and doesn’t harm the baby or mother.
- is like a special camera that uses sound waves to create pictures of the inside of the body
it is a noninvasive prenatal diagnosis or testing
cell free fetal dna testing
*ultrasound is also noninvasive
chromosomal shorthand
table 13.1
true or false:
polyploids in humans are nearly always lethal, individuals with triploids, account for 17 percent of spontaneous abortions and 3 percent of stillbirths and newborn deaths
true - very rarely, an infant survives a few days with defects in nearly all organs
stillbirths - baby dies in the womb after 20 weeks of pregnancy. It happens before or during birth. It’s different from a miscarriage, which occurs before 20 weeks of pregnancy.
briefly explain the autosomal aneuploids
trisomy 21 (Down syndrome):
- most common & least severe
- characteristics: short stature, distinctive facial features, intellectual disabilities
- health challenges: heart defects, increased risk of leukemia, potential early Alzheimer’s development
trisomy 18 (Edward syndrome):
- more severe than down syndrome
- v short life expectancy (most do not survive infancy, few live into young adulthood), v severe physical and intellectual disabilities
trisomy 13: (Patau Syndrome)
- most severe of the three
- extreme physical abnormalities n intellectual disabilities
- v few long time survivors
Sex chromosomes aneuploids: female
45, X syndrome (Turner syndrome):
- girl is born with only one X chromosome instead of the usual two.
- shorter height, delayed or no puberty, heart or kidney probs
Triplo-X syndrome:
- a girl has three X chromosomes instead of the usual two.
- often no symptoms but may hv taller height/ learning difficulties
[Main Difference:
Turner Syndrome: Missing an X chromosome.
Triplo-X Syndrome: Extra X chromosome.]
Sex chromosomes aneuploids: male
47, XXY Syndrome (Klinefelter syndrome):
- one extra X chromosome
- taller than average, less facial and body hair, sometimes difficult w fertility, learning or social challenges
47, XXYY Syndrome:
- h two extra chromosomes—one X and one Y
- similar symptoms to Klinefelter syndrome, possible behavioral and emotional challenges
47, XYY Syndrome (XYY syndrome):
- one extra Y chromosome
- taller than average height, most have noral fertility and health, some may have mild learning or speech delays
[47, XXY (Klinefelter): Extra X, often affects puberty and fertility.
47, XXYY: Extra X and Y, more learning/behavioral challenges.
47, XYY: Extra Y, fewer issues, mostly taller and mild learning delays.]
Modern methods for early detection of genetic disorders
Genetic screening
[What it is: Tests to check if a person or baby might have a genetic disorder.
Purpose: To identify risks or detect conditions early, such as Down syndrome, cystic fibrosis, or sickle cell anemia.
Examples:
Prenatal screening: Tests during pregnancy, like blood tests or ultrasounds.
Carrier screening: Tests before pregnancy to see if parents carry genes for certain conditions.]
Remove or add part of genes/ chromosomes. Used for potential treatments
Gene editing
- Potential treatments like genome editing for conditions such as down syndrome
[Gene Editing
What it is: Changing the DNA to fix or improve genes.
How it works: Scientists can add, remove, or fix parts of the DNA using tools like CRISPR (a precise “gene scissor”).
Purpose: To prevent or treat genetic conditions.]
what are the traditional techniques for prenatal techniques for prenatal chromosomes analysis
Karyotyping:
Makes a picture of all the baby’s chromosomes to check for abnormalities like missing or extra ones.
Slow but gives a full overview.
FISH (Fluorescence In Situ Hybridization):
A faster technique that looks for specific chromosome problems, like Down syndrome.
A modern genetic test that compares the baby’s DNA to normal DNA to spot tiny changes.
Comparative Genomic Hybridization (CGH)
- used to detect very small CNVs (copy no. variation) which are termed microdeletions and microduplications
- CGH compares he no. of copies of a CNV in the same amt of DNA
- More detailed than karyotyping or FISH (Uses DNA from amniocentesis or CVS samples
