Meiosis and Abnormal Trisomies Flashcards
why do we need meiosis
sense of genetic diversity
allow 46 chromosomes, to become 23 each,then result in 46 again
How to characterize human chrome with karyotype
size
centromere index=short arm length/total chromosome lengthx100
g-bright-low AT/GC ratio, rich in SINE repeats and Allu sees, early rep, contain housekeeping genes, not tissue specific, rich in transcribed genes
Meiosis 1
-diplod cells replicate DNA at end of prophase 1 as sister CHROMATIDS
Metaphase/aniphase 1-alignment/disjuction of replicated homologues
Meissis 2
separation of sister chromatids
Prophase I-pariting of replicated homologous chromosomes at synapse
-pariting of replicated homologous chromosomes at synapse
Metaphase I
Chromosomes ordere din middle of cell along metaphase plate
Anaphase I
Chiasmama at chromosome edsn. Disjuction
Interkinesis I
Formation of nut and 2 daughter cells
Meiosis II
Prophase II without DNA synthesis, metaphase II, anaphase II, with 4 final haploid cells
Nondisijuction of meiosis I+result
No separation of homologs
Two disomic gametes and two nullisomic gametes
Nondisjunc at meiosis II+result
no seperation of chromatids
Two normal gametes and 1 disomic gamete/1 nullisomic gamete
Klinefelter syndrome
NDE (non disjunction event)
47, XXY, males, tall , hypogonadism, social pathology, more X=greater risk of mental retardation
Edwards syndrome
47, X, +18
IUGR-many organs messed up-clenched hands
IUGR
Intra uternine grwoth retardation
Patau syndrome
47, X, +13
IUGR, many organs messed up and polydactylyl
Downs, diagnosis in baibes and adults
47, XX, +21
Most common cause of mental retardation
Babies-tranverse palmar crease, round head, heart defect
We are doing much better at handling treatment-living to 60 and finding jobs
Turner syndrome
45, X
Gonaladal problems and short stature
Aneuploidy
Too many/too little chromosomes in zygotes
CA repeats
At begging of p-arm or q- arm
differentiate between M1 (heterozygosity for alleles close to centromere) vs M2-homozygosity for allies close to centromere
practice question-if still don’t understand ask
Sex difference in meiosis
M1/M2 in puberty-results in 4 spermatids
Meiosis in females-M1 in inauterine development-stops before birth
-oogonia arrested in Dictyotene
M1 is completer with extrusion of 1st polar body at time of ovulation, completion of second occurs at fertilization
-results in 1 mature oocyte and 2 lost polar bodies
what results in genetic uniqueness
random distribtion of homo chroms
Formation of chasmatata among non-ssister chromatids resulting in crossing over
Balance recriprocol translocation
How many balanced
How to ]ensure does not result in problem baby
Parents are normal, kids probably are not
Translations raise is of aneuploidy because synapsis of translated chrome is driven by DNA homology and messed up chrome-quadi radical (form + shape) will probably not set properly
Only 2 out of 16 segregations would be balanced
Use IVF, PGD, and CVS to ensure not bad child
(preimplantation genetic diagnosis)
Acentric/dicentric chromatids
Also coupled with duplications and deletions
In M1
Inversion, synapsis, recombination, two kinetchocres on 1 strand, other will get deleted
X inactvation+with mutations+where start
Random @ blastocyte stage for dosage compensation
X-deltions are preferentially methylated
X translocations that are balanced are preferentially NOT methylated
starts at Xic then spreads
-xist vs tsix-xist adds methyation
Females are all mosaic-non-random x inactivation with having x linked disorder
How to manifest x linked condition 100% of time for females
Females are all mosaic-non-random x inactivation with having x linked disorder or homozygous
Uniparental disomy
Get two chromasomes from 1 parent, and other parents passes a bad one but bad one is lost during mitosis
Fetal phenotype determined y 1. degree of mosaicist, 2. genomic imprinting, 3. non mendelian expression
Basically saying weird shit can happen
Duchenne Muscular Distrophy
DMD gene
79 exons
Most people have deletion in 1 or more if have disease
Imprinting
Specific parent of originen control on expression of some genes
Epienetic
Changes in gene expression due to envrionment
PWS vs AS
Prader willi vs angleman
PWS-Paternal deletion-short stature, very fat
AS_readation, inappropriate laguht-maternal deletion of same gene
Often deletion is due to methylation (where a imprinting center gene upstream was mutated/deleted)
Screening
Can be done on parents for kids, in second trimester/third
Aminicenteiss, CVS-these all have some fisk associated with them
Let patients deicde what they want
