Chromosomal Abnormalities Flashcards
where are gene-poor vs gene-rich genes located on the chromosome
Gene poor- nuclear periphery
gene rich- nuclear interior
what are chromatin? how does it make up the nucleosome core particle
they are chromosomes complexed into nucleoprotein structures in eukaryotes.
chromatin bound in nucleosomes with 2 molecules each histone make nucleosome core particles
least to most condensed chromosome state
LEAST: nucleosome
solenoid
chromatin fiber
MOST: metaphase chromasom
T/F chromosome number directly correlates to genome size and number of genes
FALSE
T/F in mammals the number of chromosomes is proportional to size/amount of DNA
FALSE
non mammalian species maximum and minimum number of chromosomes recorded
Max: fern(ophioglossum reticulum)-631 pairs
Min: nematode-1 chromosme
jack jumper ant-1(male)/2(worker) chromosomes
C-banding chromosome staining
only centromeres are stained
G-banding chromosome staining
due to differential staining along the length of each chromosome
ZOO-Fish chromosome staining
cross-species chromosome painting(show where genes from one chromosome different chromosomes from other species)
what is nondisjunction? how does it affect ploidy
it is the failure of chromosomes and sister chromatids to properly separate during cell division, it can lead to abnormalities in chromosome number
aneuploidy vs euploidy
aneuploidy: abnormal amount of chromosomes in 1 or more parts of a set of chromosomes
euploidy: chromosome number of an individual is the number of complete sets
how do disjunction errors in meiosis I vs meiosis II effect gametes?
nondisjunction in meiosis I: all gametes have abnormal number of proteins(2 have +1, 2 have -1)
nondisjunction during meiosis II: half the gametes have abnormal chromosome numbers, half are normal
is it better to have a disjunction error in meiosis I or meiosis II
meiosis II
T/F trisomy for many different chromosomes is routinely observed in spontaneous abortions
TRUE
3 human chromosomes that can be trisomic in newborns
13, 18, 21
why is autosomal trisomy more tolerable in smaller chromosomes
small chromosomes hold less DNA
main categories of structural aberrations that can occur in mammalian chromosomes
chromosome breaks
terminal deletion
acentric
does odd or even ploidy decrease fertility leading to seedless varieties
odd
acentric definition. how does it occur after chromosome break and terminal deletion
chromosome lacks a centromere. it is a fragment of a broken/deleted chromosome. it can get lost during division
what is inversion? what are its consequences?
rearrangement in chromosomes, mostly normal unless genes are disrupted
2 types of inversion and their products
parAcentric: centromere is outside of inverted region
PerIcentric: centromere is within inverted region
what inversion leads to tobiano coat color in horses
paracentric
what is a deletion, and what are its phenotypic consequences
loss of a part of one chromosome arm
-small deletions often have no phenotypic effect
-large deletions can be lethal
syndrome used as example for deletion? where was the deletion
Cri-du-chat syndrome
segmental deletion of chromosome 5p
3 main types of translocation
-nonreciprocal translocation
-reciprocal balanced translocation
-Robertsonian translocation/chromosome fusion
what type of translocation has developed the Philadelphia chromosome
reciprocal balanced translocation
possible consequences for translocation of gametes
change to the phenotype
EX. familial down syndrome caused by Robertsonian translocation
definition of duplications? how can they effect the genome
production of extra gene copies.
part of genetic material is larger, widespread segmental duplications can lead to large-scale rearrangements
what gene is involved in Charcot-Marie-tooth syndrome
chromosome 17 on peripheral myelin protein PMP22 gene
what is a fragile site? can they become common?
heritable loci on chromosomes that are visible as gabs/breaks due to cell exposure to DNA replication inhibitors. can be common or rare
are fragile sites associated with diseases all the time
only rare fragile sites are associated with diesease
example of a human disease with fragile sites, what is its mechanism
Fragile X syndrome
caused by repeats in FMR1 gene
Klinefelter syndrome
-genotype
-phenotype
-more than 1 X chromosome(XXY, XXXY, XXXXY)
-phenotypically male, tall, long-limbed, underdeveloped sex characteristics, infertile
turner syndrome
-genotype
-phenotype
-absence of a second X chromosome(XO)
-phenotypically female, webbed neck, heart and kidney defects, infertile
XXX/XXY condition
XXX-female, mostly normal, taller, infertile
XXY-male, physically normal, over 6ft tall
nucleosome structure
histone H2A and H2B make 1 dimer and H3 and H4 form another. 2 H3-H4, and 2 H2A-H2B dimers pair to form the octamer which is then wrapped with DNA
what does “beads on a string” refer to
chromatin in least condensed state.
“beads” are nucleosomes
“string” is linker DNA
what histone acts as linker DNA
H1
what gives chromosomes their shape
chromosome scaffold
euchromatin vs heterochromatin
Euchromatin: uncoiled and active DNA(white bands)
heterochromatin: condensed and inactive DNA(gray/black bands)
fluorescent in situ hybridization(FISH)
use of gene-specific molecular probes to detect a target sequence
mammalian species with most and least chromosomes
MOST: red vizcacha rat-2n=102
LEAST: Indian muntjac deer-2n=6/7
monosomy in humans
embryos are aborted or are non-viable if born
what is an inversion loop? what does it result in?
it is an alignment of a normal chromosome with its inverted homolog. it results it 2 viable gametes, and 2 nonviable/deleted gametes
genetic consequences of deletions
-loss of chromosome segments
-loss of gene(s) and gen products
-problems in meiotic pairing
-possible changes in phenotype
what is translocation
movement of chromosomal segment to a new location in the genome
nonreciprocal translocation
one chromosome translocates but the other doesn’t
reciprocal balanced translocations
two pieces of nonhomologs switch places
Robertsonian translocation
fusion of 2 nonhomologous chromosomes(decreasing the chromosome count by 1)
T/F disorders of sex development are caused by non-disjunction
FALSE. they are caused by mutations in sex-determining genes
XX male DSD
what causes it?
phenotypic changes
-SRY robertsonian translocation to X
OR
-mutation in SOX9 gene
disorders of sexual development and reproduction
XY female(swyer syndrome)
how is it caused
phenotypic changes
-deletion or mutation in SRY gene
OR
mutation in X-linked or autosomal genes
mostly normal, tall, sterile
