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86 Cards in this Set

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sister chromatids
identical strands that comprise a doubled chromosome-chromosomes can also consist of single chromatids
centromere
region of chromosome that binds sister chromatids together
metacentric
p and q arms approx same length
submetacentric
p arm significantly shorter tha q arm
acrocentric
p arm consists of satellite DNA (rDNA + telomere)
telocentric
p arm completely lacking-not normally found in humans
prophase
-formation of mitotic spindle
-two pairs of centrioles migrate to opposite poles of cell
-spindle fibers radiate out from centrioles and will attach to kinetochores
-nuclear membrane dissolves
-nucleoli disappear
-condensation of chromatin into chromosomes
metaphase
-spindles move chromosomes to equator
anaphase
sister chromatids separate at the centromere to yield two identical chromosomes which then begin to migrate to opposite poles of the cell
telophase
-nuclear membrane reforms
-chromosomes disperse into chromatin
-spindle apparatus disassembled
-cytokinesis: division of ccytoplasm to yield two cells
meiosis
converts diploid cells to haploid cells during the formation of gametes-fusion of gametes at fertilization restores diploid number
meiosis I
produces two haploid cells but chromosomes still consist of two chromatids
prophase I
similar to P in mitosis but have substages:
1.leptoteme
2.zygoteme
3. pachyteme
4. diploteme
5. diakinesis
leptoteme
chromatin begins to condense into elongated chromosomes. Start seeing it: looks like strings
zygoteme
based on homology, homologs pair side-by side to form bivalents (seen in pairs). In mitosis it didn't really matter, but now we are going to manipulate them in order to pair up the homologs based on homology (similar DNA sequences)
pachyteme
formation of synapses resulting in tetrad structures-crossing over begins to occur: exchange pieces and results in enetic shuffling. At this point talk of tetrad structure because can see all four sister chromatids
diploteme
chiasmata evident b/w homologous chromatids. chromosomes have gotten shorter and fatter
diakinesis
terminalization occurs as the chiasmata move toward the telomeres. Don't just come undone, but slide to tips until separate. Also, loss of nuclear membrane and nucleoli, formation of spindle apparatus
anaphase I
homologs begin migrating to opp. poles. End result is that you get one of each numbered homolog in each cell. Gone from diploid to haploid.
1. law of independent assortment-don't know which direction mother and father's chromosomes will go.
2. non-disjunction-homologs fail to segregate properly
telophase I
typically does not continue through completion
meiosis II
produces four haploid cells w/ chromosomes consisting of one chromatid. analogous to mitosis. will pull sister chromatids to opposite poles.
nondisjunction
don't have proper separation of chromatids. cacn end up with two chromatids in one cell that is supposed to be haploid and other that don't have any-chances are death in utero
how obtain human chromosomes
most common source is WBC's. can't do RBCs because don't have DNA. Force WBCs to replicate
method for getting chromosomes
step 1
1. skin scrapings (determine mosaicism)
2. fetal sources
3. add colcemid to rapidly growing cells-arrested mitosis in prometaphse and inhibits mitotic spindle from forming
4. add hypotonic saline
5. burst cells open on microscope slides
getting chromosomes step 2: banding
1. G (giemsa) staining: most common method. Stronger base pairing=darker stain (G-C)
2. R (reverse) staining: produces opposite light/dark pattern of G staining. Used if you think there is something missing in the telomere, for example
3. C (centromere heterochromatin) staining:wil show centromere sections better-if you think there is something missing from centromere in original stain
4. high resolution banding: begins w/ early prophase chromosomes-single G band may be subdivided into 5-15 sub-bands. may be able to make a microdelition
karyotype
photomicrograph of individual's chromosomes. can diagnose chromosome number abnormalities. allows determination of numberical and structural abnormalities
aneuploidy
abnormal chromosome number due to gain or loss of chromosomes. result from nondisjunction: missing a chromosomes or have extra one. Can occur in Meiosis I or II.
meiotic non-disjunction
can produce disomic or nullisomic gametes. nondisjunction during meiosis I increases with increased maternal age due to stasis in diploteme
mitotic non-disjunction
occurs in utero-results in some normal and some abnormal cells within the same individual (mosaicism) For ex: severity of down's syndrome can vary b/c could have 2/3 normal cells
polyploidy
cell contains one or more extra sets of chromosomes. incompatible with human life.
potential causes of polyploidy
1. failure of meiotic division in egg or sperm: did not separate homologs or sister chromatids in Meiosis II
2. dispermy: two sperm simultaneously fertilize a single ovum
unbalanced rearrangement
translocation: net loss or gain of chromosomal material: usually has serious clinical effects
balanced rearrangement
no net gain or loss of chromosomal material. greater chance of having children with unbalanced chromosomal make up
translocation
the transfer of genetic material from one chromosome to the end of another-affect fertility. leads to decreased fertility. genetic material is moved, but all is present.
reciprocal translocation
when two chromosomes exchange terminal pieces of genetic material. can see tetrad structure in Meiosis I which allows for all the part to match up even though parts of them have switched w/ another chromosome. In anaphase, will separate in order to be compatible with life. Out of 6 gametes, only 1/3 will result in viable offspring.
robertsonian translocation or centric fusion
when two acrocentric chromosomes lose their satellite DNA and fuse together. Will pair up in a trivalent structure and also causes decrease in fertility.
insertion
fine for first person, but would result in problems with offspring if get duplicates-when genetic material from one chromosome gets placed internally within another chromosome. decreased fertility.
inversion
portion of a chromosome breaks and the "flips" before reattaching. decreased fertility due to effect of crossovers within inverted region centromere. effected person if fine b/c it's just that genes are not in proper order
pericentric inversion
inverted segment contains centromere
-will hav partial trisomies and monosomies
--if crossover occurs in inverted region get nonviable offspring: possibility of having a normal child dependent on size of inverted region. Smaller inversions are much better: not as likely to have a crossover since crossovers tend to be random events.
paracentric inversion
inverted sequence does not contain centromere. as long as no break within a gene, person will be fine
-. will get some that do not have a centromere (which is where spindle attaches)-therefore chromosomes cannot be manipulated and it just stays in the middle.
-find DNA in cytoplasm if microbial infection, therefore have enzymes that breakdown DNA. So, with chromosome without centromere cannot be moved, gets stuck in the middle and gets in to cytoplasm when cells split. Gets digested.
B. Get some that have two centromeres. Could be pulled in different directions and break. Get pieces going to different sides. On top of that you have repetitive sections and some sections missing. Chromosome gets lost or broken.

1. larger the inversion, greater possibility of crossing over and nonviable offspring.
2. phenotypically normal
3. produces nonviable children
ring chromosome
result breaks at both telomeres >> sticky ends join together (Emery Figure 3.32)-will show signs of problems (trouble is when DNA is replicated) Sister chromatids end up being interlocked and options are that they go together or they break, sometimes in multiple pieces
isochromosomes
results from the loss of one chromosomal arm and subsequent duplication of the remaining arm >> most commonly seen on the X chromosome (by definition, is metacentric since you are duplicating it. Problem arises due to several reasons: missing all the genes that were on the original arm and have trisomy of replicated section).
** one to survive is the X chromosome** Will have some complications.
FISH
fluorescent in situ hybridization
-sequence specific probes – allow detection of microdeletions and microduplications
-centromeric probes for specific chromosomes – allow detection of aneuploidy (won't pick up translocation)
-telomeric probes for specific chromosomes – allow detection of very small subtelomeric deletions and translocations >> useful in diagnosis for unexplained mental retardation
-whole chromosome painting: used to detect subtle translocations
chimerism
when an individual has two chromosomally distinct cell populations that were derived from different zygotes. Subtle chromosomal differences.
dispermic chimera
two zygotes fuse to form a single embryo
blood chimera
exchange of cells between non-identical twins via the placenta
heritable mutations
occurs within gametes: passed one generation to the next
autosomal dominant inheritance
manifested in heterozygous state
-assume this b/c it is rare, and the odds of them being homozygous is even more rare
pleiotropy
disorder involves more than one organ system
variable expressivity
when the severity of a genetic disorder shows significant differences in different affected individuals >> occurs with both dominant and recessive
-stems from the idea that there are other genes coming in to play
reduced penetrance
when individuals with a genetic disorder fail to demonstrate clinical symptoms >> probably due to interactions with other genes-genetically have it, have the genotype, but for some reason it is not expressed. Found particularly in recessive disorders. Important b/c can still pass on to offspring.
de novo mutation
affected individual could be a mosaic (somatic mutation) or mutation could have occurred in a parental germ line
-Can have it affect germ cells as well. Trait never seen before in family history, but shows up in all offspring.
locus heterogeneity
when two or more different loci (genes) can produce the same disorder >> also found with a few dominant traits
allelic heterogeneity
when the recessive alleles actually can result from mutations at more than one site within a gene
pseudoautosomal regions
where X and Y match up for meiosis-on very tips
ring chromosome
result breaks at both telomeres >> sticky ends join together (Emery Figure 3.32)-will show signs of problems (trouble is when DNA is replicated) Sister chromatids end up being interlocked and options are that they go together or they break, sometimes in multiple pieces
isochromosomes
results from the loss of one chromosomal arm and subsequent duplication of the remaining arm >> most commonly seen on the X chromosome (by definition, is metacentric since you are duplicating it. Problem arises due to several reasons: missing all the genes that were on the original arm and have trisomy of replicated section).
** one to survive is the X chromosome** Will have some complications.
FISH
fluorescent in situ hybridization
-sequence specific probes – allow detection of microdeletions and microduplications
-centromeric probes for specific chromosomes – allow detection of aneuploidy (won't pick up translocation)
-telomeric probes for specific chromosomes – allow detection of very small subtelomeric deletions and translocations >> useful in diagnosis for unexplained mental retardation
-whole chromosome painting: used to detect subtle translocations
chimerism
when an individual has two chromosomally distinct cell populations that were derived from different zygotes. Subtle chromosomal differences.
dispermic chimera
two zygotes fuse to form a single embryo
blood chimera
exchange of cells between non-identical twins via the placenta
heritable mutations
occurs within gametes: passed one generation to the next
autosomal dominant inheritance
manifested in heterozygous state
-assume this b/c it is rare, and the odds of them being homozygous is even more rare
pleiotropy
disorder involves more than one organ system
variable expressivity
when the severity of a genetic disorder shows significant differences in different affected individuals >> occurs with both dominant and recessive
-stems from the idea that there are other genes coming in to play
reduced penetrance
when individuals with a genetic disorder fail to demonstrate clinical symptoms >> probably due to interactions with other genes-genetically have it, have the genotype, but for some reason it is not expressed. Found particularly in recessive disorders. Important b/c can still pass on to offspring.
de novo mutation
affected individual could be a mosaic (somatic mutation) or mutation could have occurred in a parental germ line
-Can have it affect germ cells as well. Trait never seen before in family history, but shows up in all offspring.
locus heterogeneity
when two or more different loci (genes) can produce the same disorder >> also found with a few dominant traits
allelic heterogeneity
when the recessive alleles actually can result from mutations at more than one site within a gene
pseudoautosomal regions
where X and Y match up for meiosis-on very tips
-form chiasmata with X
nonrecombinant region of Y
-sig amt of heterochromatin (non-coding_
-tests specific genes
-sex determining region
lyon hypothesis
o 1. in utero at ~ 5000 cells >> all but one X chromosome inactivated in each cell. Each daughter cell maintained this. If parent cell has paternal chromosome turned off, daughter cells will as well. Never reactivate the other X.

o 2. which chromosome inactivated is random

3. same chromosome inactive in all daughter cells
skewed x activation
disorder carrying X chromosome primary activated chromosome in tissue affected by disorder >> manifesting heterozygote-most common: hemophilia
X-linked dominant inheritance
resembles autosomal but more females than males affected
autosomal dominant
(1) males and females equally affected

(2) affected individuals in each generation

(3) all forms of gender transmission possible
autosomal recessive
(1) males and females equally affected

(2) trait can skip one of more generations
X-linked recessive
(1) males most commonly affected

(2) transmitted through unaffected females

(3) never transmitted father to sons
X-linked dominant
(1) females more commonly affected than males-2 X’s, so have twice the chance of getting.

(2) affected males can transmit trait to daughters but not to sons
anticipation
ex: huntingtons- gets worse with each generation or starts at a earlier age
somatic mosaicism
only a certain portion of somatic cells affected >> accounts for varying degrees of severity of certain disorders among mosaics Ex: Down’s Syndrome- different levels of severity. Won’t necessary pass on to future generations, unless affects egg or sperm.
uniparental disomy
rare situation when an individual has a set of homologs that were both derived from the same parent
uniparental isodisomy
error in meiosis II resulting in two copies of the same homolog
-in meiosis two, there is a set of sister chromatids that don’t split correctly and end up with two of them in one cell. Partner up with one from the other parent that ends up with three in one cell. Mechanism to get rid of extra chromosomes causes loss of the single chromosome; could randomly kick out the one from the other parent. Sister chromatids are exact copies of each other, hence the iso in isodisomy.
-can end up with recessive trait even though only one parent carried it
uniparental heterodisomy
error in meiosis resulting in both homologs from a single parent
-Have problem of no separation of homologs in meiosis 1, and then with separation of chromatids, end up with two in each cell, but are chromatids from different homologs.
genomic imprinting
where depends on whether mutation came from mother or father
-prader-wili or angelman's
polygenic inheritance
non-Mendelian inheritance in which the phenotype is dependent on the additive effect of several genes at different loci Ex: hair color
-understand multiple alleles and polygenic inheritance differences.
multifactorial
(polygenic: just genes, a little environmental) inheritance – non-Mendelian inheritance in which the phenotype is determined by multiple genes and environmental factors- more prominent in multifactorial than polygenic >> many developmental anomalies
-liability curves and monozygotic twins