Lesson 4 : CHROMOSOMES Flashcards
Primarily consist of DNA and protein.
CHROMOSOMES
Essential parts of Chromosomes
■ Telomeres
■ Origins of replication sites
■ Centromere
Largest constriction of the chromosome and where spindle fibers attach.
CENTROMERE
Bases that form the centromere are repeats of a
171-base DNA sequence
_______ is passed to next generation.
CENP-A
Chromosome region between the centromere and telomeres.
SUBTELOMERE
Subtelomere consists of ____ to ____ bases.
8000 to 300,000
Subtelomere contains at least ____ protein-encoding genes. About 50% are multigene families that include _______.
500
pseudogenes
Define KARYOTYPE
● Chromosome chart.
● Major clinical tool.
● Displays chromosomes arranged by size and structure.
Humans have ___ chromosome types
_____ are numbered 1-22 by size
______ are X and Y
Humans have 24 chromosome
types.
■ Autosomes are numbered 1-22 by size
■ Sex chromosomes are X and Y
Karyotype Benefits
● Confirm a clinical diagnosis.
● Reveal effects of environmental toxins.
● Clarify evolutionary relationships.
CENTROMERE POSITIONS
● Telocentric - At the tip.
● Acrocentric - Close to center.
● Submetacentric - Off-center.
● Metacentric - At center.
○ Fetal tissue
○ Adult tissue
○ Fetal tissue
■ Amniocentesis
■ Chorionic villi sampling
■ Fetal cell sorting
■ Chromosome microarray analysis
○ Adult tissue
■ White blood cells
■ Skin-like cells from cheek swab
Chromosomes are extracted, then stained with a combination of _________ and _______
dyes and DNA probes
_________ detects about ______ of the more than ______ known chromosomal and
biochemical problems.
AMNIOCENTESIS
1000
5000
In Amniocentesis Ultrasound is used to ___________.
follow the needle’s movement
Define CHORIONIC VILLUS SAMPLING
● Performed during 10-12th week of pregnancy.
● Provides earlier results than amniocentesis.
● Does not detect metabolic problems.
● Has greater risk of spontaneous abortion.
____________ correspond to _____ copies of ___________.
Fluorescent dots
three
chromosome 21
● Schematic chromosome map.
● Indicates chromosome arms (p or q)and major regions delineated by banding patterns
IDEOGRAM
Karyotype may be abnormal in:
○ Chromosome number
○ Chromosome structure
Abnormal chromosomes account for at least ____ of ____________.
50%
spontaneous abortions.
People are being diagnosed with chromosomal abnormalities due to _______________.
improved technology
Extra chromosome sets
Polyploidy
An extra or missing chromosome
Aneuploidy
One chromosome absent
Monosomy
One chromosome extra
Trisomy
___________ and __________ proved direct detection of _____________.
Amniocentesis and chorionic villus sampling
extra chromosomes
____________ offer an indirect method
Maternal serum markers
Cell-free DNA Testing can ve performed at least __ weeks into pregnancy
10 weeks
In cell-free DNA Testing up to 20 percent of these pieces
come from the ________, and thus
represent the ____________.
placenta
fetal genome
______ cells have three sets of chromosomes. Produced by:
Triploid
■ Fertilization of one egg by two sperm
■ Fusion of haploid and diploid cells
Those born with aneuploidy are more likely to have____________ rather than _______.
an extra chromosome (trisomy)
a missing one (monosomy)
Aneuploidy arises during _______, producing groups of _________ with the extra or missing chromosomes.
mitosis
somatic cells
Individual with two chromosomally-distinct cell populations is called a _________.
mosaic
_________ cease developing as embryos or fetuses.
Autosomal aneuploids
Frequently seen _________ in newborns are those of chromosomes ___,____, and ___.○ Carry fewer genes than other autosomes.
trisomies
21, 18, and 13
● Most common trisomy among newborns.
● Distinctive facial and physica lproblems.
DOWN SYNDROME
TRISOMY __
● Due to nondisjunction in meiosis II cccc in oocyte and generally do not survive
.● Serious mental and physical disabilities.
● Distinctive feature - Oddly clenched fists.
TRISOMY 21
EDWARDS SYNDROME
TRISOMY ___
● Very rare and generally do not survive 6 months.
● Serious mental and physical disabilities.
● Distinctive feature - eye fusion.
TRISOMY 13
PATAU SYNDROME
TRISOMY __
● One in 2500 female births.
● 99% of affected fetuses die in utero.
● Features:
○ Short stature
○ Webbing at back of neck
○ Incomplete sexual development (infertile)
○ Impaired hearing
● Individuals who are mosaics may have children.
TRISOMY 13
TURNER (XO) SYNDROME
TRISOMY __
● One in 1000 female births.
● Few modest effects on phenotype include tallness, menstrual irregularities, and a slight impact on intelligence.
● X inactivation of two X chromosomes occurs and cells have two Barrbodies.
● May compensate for the presence of extra X.
TRISOMY 13
TRIPLO-X SYNDROME
TRISOMY __
● One in 500 male births.
● Phenotypes include:
○ Incomplete sexual development
○ Rudimentary testes and prostate
○ Long limbs, large hands, and feet
○ Some breast tissue development
● Common cause of male infertility
TRISOMY 13
KLINEFELTER (XXY) SYNDROME
TRISOMY __
● Arises due to unusual oocyte and sperm.
● Associated with more severe behavioral problems than Klinefelter syndrome.
○ AAD, obsessive-compulsive
disorder, learning disabilities
● Individuals are infertile.
● Treated with testosterone
TRISOMY 13
XXYY SYNDROME
TRISOMY __
● One in 1000 male births
● 96% are phenotypically normal
● Modest phenotypes
○ Great height
○ Acne
○ Speech and reading
disabilities.
● Studies suggest increase in aggressive behaviors are not supported.
TRISOMY 13
JACOBS (XYY) SYNDROME
Missing genetic segment from a chromosome.
DELETION
Deletion is often not inherited, rather they arise
de novo
Larger deletions increase the likelihood that there will be an ______
associated phenotype
Deletion 5p
Cri-du-chat (cat cry) syndrome.
● Presence of an extra genetic segment on a chromosome.
○ Often not inherited.
○ Rather they arise ____.
DUPLICATION
de novo
Duplication’s effect on the phenotype is generally dependent on their
size
Two nonhomologous chromosomes exchange segments.
TRANSLOCATIONS
Translocations types :
○ Robertsonian Translocation
○ Reciprocal Translocation
Two nonhomologous acrocentric chromosomes break at the centromere and their long arms fuse.
ROBERTSONIAN TRANSLOCATIONS
Translocation carriers have __ chromosomes. Produce _________ gametes.
45
unbalanced
__ of Down syndrome results from a ________________ between chromosomes ___ and _____.
5%
Robertsonian translocation
21 and 14.
Tends to recur in families, who also have more risk of spontaneous abortions.
TRANSLOCATION DOWN SYNDROME
Two nonhomologous chromosomes exchange parts
RECIPROCAL TRANSLOCATIONS
_________ : Chromosome segment that is flipped in orientation. ______ cause health problems probably due to ______ at the _______. May impact ___________.
INVERSIONS
5-10%
disruption of genes
breakpoints
meiotic segregation
Inverted region does not include centromere.
Paracentric inversion
Inverted region includes centromere
Pericentric inversion
● Chromosomes with identical arms.
● Formed when centromeres divide along the incorrect plane during meiosis.
ISOCHROMOSOMES
● Occur in 1 of 25,000 conceptions.
● Arise when telomeres are lost and sticky chromosome ends fuse.
● Genes can be lost or disrupted causing symptoms.
RING CHROMOSOMES
TRAITS INHERITED ON SEX CHROMOSOMES
Passed from fathers to sons only.
Y-Linked Traits
TRAITS INHERITED ON SEX CHROMOSOMES
○ Passed from mother to son because he inherits his X from his mother and his Y from his father.
○ May be dominant or recessive.
○ X-linked dominant traits are more devastating to males.
X-Linked Traits
Shuts off one X chromosome in each cell in female mammals making them mosaics for heterozygous X-linked genes.
X INACTIVATION
In humans, it can be used to identify carriers of some X-linked
diseases such as _______ in which an affected boy has ___________.
Lesch-Nyhan syndrome
cerebral palsy
