Cytogenetics - 2 lectures Flashcards by Vanessa Nwaokocha

accounts for large number of spontaneous abortions

chromosomal abnormalities

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types of numerical chromosomal abnormalities

euploidy (polyploidy): number of chromosomes is in multiples of 23 –>triploidy (69) so has 3 copies or tetraploidy (92) so has 4 copies

aneuploidy: monosomy or trisomy

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are euploidy compatible with life

nah

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three common autosomal aneuploidy

trisomy 21 (Down Syndrome)
trisomy 18 (Edward Syndrome)
trisomy 13 (Patau Syndrome)

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two sex chromosome aneuploidy

Turners Syndrome (45X)
Klinefelters Syndrome (47XXY)

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most common liveborn autosomal trisomy

Down Syndrome

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risk factors of Downs

increased maternal age increases risk of meiotic nondisjunction during oogenesis (with meiotic I nondisjunction being more common)

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features of Downs

short, intellectual disability, congenital heart defects, single palmar crease, epicanthal folds, depressed nasal bridge, upslanting palpebral fissure

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persons with downs is likely to develop what disorder and why

Alzheimers at a much younger age because genetic factors for alzheimers are on chromosome 21

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what is chromosomal number for down syndrome

47, XX or XY, +21

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features of edwards

clenched fist with overlapping fingers, rocker bottom feet, low set ears, smaller jaw (micrognathia), congenital heart defects, microcephaly, intellectual disability

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genetic mechanism of edwards and patau

nondisjunction during oogenesis

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chromosomal number of edwards

47, XX or XY, +18

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features of patau

polydactyly, cleft lip and palate, microphthalmia, microcephaly, cardiac abnormalities, intellectual disability

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chromosomal number of patau

47, XY or XX, +13

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genetic mechanism of Turners and Klinefelters

nondisjunction during meiosis

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features of Turners

X chromosome monosomy, webbed neck, short, cystic hygroma at birth (neck swelling), amenorrhea (no menstruation), gonadal dysgenesis, ‘streak ovaries’

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what syndrome is associated with not having barr bodies

turners (45X) - no second X to have inactivated

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features of Klinefelters

testicular atrophy, gynecomastia, female distribution of hair, infertile

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chromosomal number of Klinefelters

47XXY

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nondisjunction is most common in who and when

females during meoisis I

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are the two maternal chromosomes from nondisjunction meiosis I identical

no - two different alleles

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XXX female is a result of?

meiosis I and II nondisjunction in mom

meiosis II nondisjunction in dad

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XYY fetus is a result of?

meiosis II nondisjunction in father

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Klinefelters is a result of

47XXY meiosis I and II nondisjunction in mom meiosis II nondisjunction in dad

How do you differentiate between meiotic and mitotic nondisjunction?

mitotic nondisjunction is less severe there will be areas of the body without trisomy or areas with different percentages of nondisjunction in mitotic nondisjunction

A newborn infant with a single palmar crease and depressed nasal bridge is suspected to have a genetic disorder. The karyotype analysis shows the presence of 100 cells of the karyotype 47,XX,+21. The most common mechanism that leads to this karyotypic abnormality is

nondisjunction during oogenesis | trisomy 21

difference between balanced and nonbalanced structural chromosomal abnormalities

balanced - there is no net gain or loss of genetic material unbalanced - there is a net gain or loss of genetic material

exchange of genetic material between non homologous chromosomes

reciprocal translocation | chromosomes are derivatives

effect if reciprocal translocation occurs in somatic cells

possibly no change in phenotype (silent) activation of oncogene ---> cancer and can lead to increased growth rates of cells

effect if reciprocal translocation occurs in germ line cells

higher incident of spontaneous abortion in the carrier

difference between alternate and adjacent I and II segregation

alternate - balanced chromosomes | adjacent I and II - unbalanced chromosomes

Philadelphia chromosome t(9;22) results in

activation of ABL proto-oncogene in hematopoietic cells ---> chronic myelogenous leukemia this occurs in somatic cells

t(8;14) is number of what reciprocal translocation

Burkitt lymphoma (somatic cells)

In a patient with chronic myelogenous leukemia, examination of the bone marrow cells reveal the presence of Philadelphia chromosome. This is a result of

balanced reciprocal translocation - exchange between two non homologous chromosomes

Robertsonian Translocation happens between which chromosomes

acrocentric chromosomes 13, 14, 15, 21, 22

what happens in robertsonian translocation

loss of short arm of two chromosomes involved (satellite contains genetic material for RNA) fusion of the long arms of the two chromosomes involved

karyotype of robertsonian translocation

45, XX, der (14;21) (q10; q10) those last two sets of numbers will vary

trisomy 14 is a type of

adjacent segregation - unbalanced genetic material

causes of trisomy 21/ down syndrome

``` robertsonian translocation (2-5%) or nondisjunction during oogenesis ```

karyotype of down syndrome as a result of robertsonian vs. nondisjunction

robertsonian - 46, XX, +21, der (14;21), (q10; q10) | nondisjunction - 47, XX, +21

alternate segregation can result in...

normal gamete | or gamete with derivate chromosome that can result in robertsonian translocation carrier on fertilization

adjacent segregation can result in..

trisomy of chromosome involved for ex: trisomy 14 (not compatible with life) -> spontaneous abortion trisomy 21 on fertilization

A 25-year old female with a history of repeated spontaneous abortions has a 2 year old girl withDown syndrome. Karyotype analysis of the mother reveals that she is a Robertsonian translocation carrier. What is the mechanism that produced Down syndrome in this child?

adjacent translocation during meiosis

example of large deletion >4mb and what detects them

``` Wolf Hirschhorn (4p-) and cri du chat (5p-) detected by cytogenetic studies (light microscope) ```

what detects small deletion <4Mb

high resolution prometaphase banding - FISH and array CGH

does not detect balanced rearrangement

array CGH and SNP array

* Suspected deletion or duplication syndrome * Unexplained developmental delay or autism spectrum disorder * Congenital anomalies/dysmorphic features all reasons for?

cytogenetic testing

cri du chat is deletion of?

5p hence chromosome loses some of its genetic material

features of cri du chat

high pitch cat cry, severe intellectual disability, speech problems microcephaly

used to test for cri du chat

FISH and array CGH

symptoms of DiGeorge's syndrome aka 22q11 syndrome

CATCH 22 | cardiac anomalies, abnormal facial features, thymic aplasia, cleft lip and palate, hypocalcemia

increased risk of schizophrenia and most common contiguous gene

digeorges

symptoms of Wolf Hirschhorn Syndrome

deletion of 4p, facial anomalies, widely spaced eyes, prominent nose, intellectual and developmental delay, abnormal iris, cardiac anomalies

Wilms’ tumor, aniridia, genitourinary malformations, and retardation of growth and development

WAGR syndrome - small deletion

uniparental disomy is a result of?

trisomy rescue

what are inversions and what are the types

it is a flip of the chromosome pericentric - flip around the centromere paracentric - flip but does not involve centromere

how are inversions identified

karyotype analysis

results of inversion

usually balanced and no clinical problems in carrier

risk to gamete of inversion carriers

during crossover, segments of chromosome are duplicated or deleted --->dicentric and acentric (not compatible with life - spontaneous abortions)

is a deletion of a chromosome viable

no if an autosome | but is if it a sex chromosome

what happens in isochromosome

there is a loss of one arm of chromosome and a duplication in the one that is still there

isochromosome results in?

chromosomal and gene imbalance

A child with Down syndrome has the genotype 1, 2, 3 for a polymorphism on chromosome 21 that has alleles 1, 2, 3, and 4. His mother is 1,2 and father is 3,4. Where did the nondisjunction occur?

maternal meiosis I nondisjunction

when a chromosome loses genetic material at the terminal portions & the ends fuse to form a ring like structure

ring chromosome

ring chromosome is seen in what type of people

radiation worker

people often seen with X isochromosome

Turner Syndrome

gives rise to phenotype of Turner

haploinsufficiency of genes on the petite arm that escaped X inactivation

what happens to the isochromosome in Turner

it is typically inactivated