chapter 10 part 1 Flashcards
what things are species-specific about chomosomes?
chromosome size, number in a nucleus, & shape
what does each chromosome pair in a diploid genome have?
distinct size, shape, & genetic content
do all chromosomes occupy the same territory in each nucleus?
no
when does a chromosome leave the territory it has confined itself to?
once M phase is initiated
are chromosomes inactive in their territories?
no, they are active within their territories & move, & turn during transcription & DNA replication
what do chromosomes appear to be anchored in their territories by?
their centromeres
what are the regions between territories called?
inter-chromosomal regions
what are inter-chromosomal regions?
channels for movement of proteins, enzymes, & RNA molecules
where are larger, more gene-rich chromosomes generally found?
more towards the center of the nucleus, while the smaller ones with fewer genes are near the periphery
what do karyotypes allow for?
recognition of abnormalities in chromosome number or structure
-autosomes are numbered one through 22 in their descending order of size
-extra or missing chromosomes can be identifies as well as rearrangements (insertions or deletions)
-comparison between species (allows for tracing of evolutionary history of related species)
what does in situ hybridization use to detect their target sequences
molecular probes (DNA or RNA) labeled with flouresence
-multiple fluorescent labels so that each labeled chromosome can be identified with different wavelengths
what did first generation methods of in situ hybridization use
nucleotide probes labeled with P32
what does FISH stand for
fluorescent in situ hybridization
short arm
p
long arm
q
metacentric
the centromere is near the middle of the chromosome
submetacentric
the centromere is between the center & the tip of the chromosome
acrocentric
the centromere is close to one end of the chromosome
acentric
a piece of DNA without a centromere
telocentric
the centromere is at the tip of the chromosome & there is no p arm
heterochromatin
more condensed
silenced genes (methylated)
stains darker
more repetitive DNA
euchromatin
less condensed
actively expressing genes (acetylated)
stains lighter
less repetitive DNA
what does chromosome banding allow
cytogeneticists to identify each chromosome in a karyotype
what is the standard for human chromosome banding?
G (giesma banding)
human genome has how many genes & how many giesma bands
22,000 genes & 2000 giesma bands
how many genes per band
11 genes per pand
chromosome nondisjunction
the failure of homologous chromosomes or sister chromatids to separate as they normally do during cell division (mitosis or meiosis)
what can chromosome nondisjunction result in
abnormalities in chromosome number (aneuploidy)
-in somatic cells, it results in one daughter cell w an extra chromosome (2n+1) & the other with a missing one (2n-1)
mitotic nondisjunction
if at first division (zygotic) all cells are diploid
if later in development, aneuploid sectors in an organism
meiotic nondisjunction
-aneuploid haploid organisms (n+- 1)
-aneuploid gametes (n +-1) leading to aneuploid zygotes
-increased frequency if crossing over fails
results on nondisjunction in germ-line cells is what
aneuploid gametes that can produce aneuploid zygotes
-results in failure of homologs to separate (the gametes produced are either n+1 or n-1)
what does fusion of non-disjunction in meiosis 1 gametes produce?
trisomic (2n+1) or monosomic (2n-1) offspring
nondisjunction is meiosis II
failure of sister chromatids to separate
aneuploidy
alters the dosage of all the genes on the affected chromosomes
-50% less product in monosomics
-50% more product in trisomics
-most animals are highly sensitive to changes in gene dosage
-plants tolerate gene dosage changes more readily
are plants or animals more sensitive to changes in gene dosage?
animals
how many gametes will be affected in nondisjunction of meiosis II
among the four gametes, only 2 will be affected
-two normal
-one (n+1)
-one (n-1)
what do changes in gene dosage lead to
an imbalance of gene products from the affected chromosome relative to the unaffected chromosomes
are humans sensitive to changes in gene dosage?
yes, very
humans usually do not survive aneuploidy
are autosomal monosomies observed in humans?
no- only one type of sex-chromosome monosomy even is viable
what trisomies are seen in newborn infants
trisomies: 2n+1
trisomies of chromosome 13, 18, & 21 (autosomes)
what does pallister-killian syndrome occur due to the presence of?
anomalous extra isochromosome 12p, the short arm of the 12th chromosome
what does the presence of the isochromosome lead to?
development of tetrasomy 12p
what type of condition is pallister-killian syndrome?
a mosaic condition
-not all cells have the extra isochromosome
about how many pregnancies sel abort
half
how much of spontaneously aborted pregnancies carry abnormalities of chromosome number of structure?
more than half
what is trisomy 21
down syndrome
what is the link of trisomy 21 that researchers have found?
a link between risk of trisomy 21 & maternal age
what is the age that is considered (advanced maternal age)
35
what portion of the chromosome can be correlated with the majority of down syndrome symptoms?
DSCR- down syndrome critical region
what gene made a major contribution to down syndrome that is known to produce dosage-sensitive learning defects in mice & flies
DYRK
what gene has a homolog in mice & fruit flies that is associated with formation of the heart & nervous system
DSCAM
turner syndrome
a monosomy of the X chromosome with no second chromosome (X0)
-embryo survives but has developmental abnormalities
-phenotypically sterile females with other characteristics abnormalities
what gene in turner syndrome, which is not inactivated by dosage compensation, is insufficient to direct normal development
SHOX
- haploinsufficiency of this gene plays central role in producing the symptoms of the syndrome
how can mosaicism develop
as a result of mitotic disjunction early in embryogenesis
UPD
uniparental disomy (UPD)
-both copies of homologous chromosome pair arise from the same parent
what was UPD first identified in
angelman syndrome & prader-willi syndrome
-usually caused by deletion of a small region of chromosome 15
which actors son has a uniparental disomy
colin farrell’s son has angelman syndrome
possible mechanisms of UPD
-in rare cases, the same chromosome- for instance, chromosome 15- undergoes nondisjunction in both sperm & egg
-when these gametes unite, they produce an individual with two copies of chromosomes 15 from one parent & non from the other
what produces a trisomic zygote
when a nondisjunction occurs in one parent, resulting in a gamete with two copies of the chromosome (n+1) unites with a normal gamete
what happens in trisomy rescue
one copy of the trisomy chromosome is randomly ejected in one of the first mitotic divisions after fertilization
if two copies retained by the zygote are from the same parent, what results?
uniparental disomy
polyploidy
the presence of three or more whole sets of chromosomes in the nucleus of an organism
what can polyploidy result from
-a duplication of chromosome sets within a species (autopolyploidy)
-combining the chromosome sets of different species (allopolyploidy)
what does polyploidy in plants do?
increases fruit size
allopolyplody
carry multiple sets of chromosomes that originate in different species
what does allopolyploudy result in
in intERspecific hybird offsprig that is infertile because the chromosome sets are not homologous
homeologous
partially homologous chromosomes
what involved homelogous chromosomes
allopolyploidy
chromosome nondisjuction in allopolyploidy can lead to what
-cells with double the number of chromosomes so that now each chromosome has a homolog for pairing, & then the hybrid is fertile
how to allopolyploids occur
both naturally & by human manipulation
-fruit & flower size increased by polyploids
-fertility is decreased (mainly in odd number diploids)
-hybrid vigor, more rapid growth, increased fruit & flower production, improved resistance to disease occurs
triticum aestivum
bread wheat (2n=42) natural allopolyploid (n=21)
-appears to be hexaploid (6x=42)
—six sets of similar chromosomes from at least three separate varieties
agricultural applications of allopolyploidy
-plant monoploids can be induced to grow from 1n cells in anthers
-commercial bananas (3n=33), & seedless watermelons are triploids - no seeds
who wanted cabbage laves with leaves & radish roots
G. karepechencko
amphidiploid
an interspecific hybrid having a complete diploid chromosome set from each parent form
also called alleotetraploid (doubled diploid)
