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Cytogenetics

Trisomies and Robertsonian Translocations

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Group A

Group C

Group D Group E

Group F Group G

Sex Chromosomes

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q10 Centromere

p arms Regions Bands q arm

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Karyotype Edwards Syndrome

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47,XY,+21

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Review of Mitosis (regular cell division), and Meiosis (gamete formation). Meiosis results in half the number of chromosomes, so that when fertilisation there will be 2N – a diploid number of chromosomes.

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120074/bio19.swf::Stages%20of%20Meiosis

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Normal Meiosis Producing daughter cells with half the number of chromosomes

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Error in meiosis 1 Error in

meiosis 2

Trisomy – Can you see the difference? Cell on the right will lead to UPD if the Paternal chromosome is lost due to “trisomic rescue”

Fertilisation – what next?

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Mitotic “accident”

Some trisomic cells and some disomic cells producing a MOSAIC

Pure trisomy

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Down Syndrome karyotype 47,XY

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Mosaic Down Syndrome karyotype 47,XY,+21[20]/46,XY[10]

20 cells counted with 47 chromosomes including an extra chromosome 21

10 cells counted with 46 chromosomes and a normal genotype

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Parent Cell

(balanced)

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Robertsonian Translocation resulting in Down Syndrome 46,XY,rob(14;21)(q10;q10),+21

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Turner’s Syndrome

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Turner Syndrome 46,X,i(X)(q10)

isochromosome

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Turner Syndrome 46,X,r(X)

Symptoms are sometimes worse than other forms of Turner syndrome due to the absence of the Xist gene which controls X inactivation. NB no telomeres.

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Neocentric X-chromosome in a girl with Turner-like syndrome. Molecular Cytogenetics 2012 Vol: 5(1):29.

Neocentromeres are rare human chromosomal aberrations in which a new centromere has formed in a previously non-centromeric location. This structurally abnormal X chromosome with a neocentromere was found in a 15-year-old girl with clinical features suggestive of Turner syndrome, including short stature and primary amenorrhea. G-banded chromosome analysis revealed a mosaic female karyotype .

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Linda Hunt: A Celebrity with Turner’s Syndrome

Linda Hunt was born on April 2, 1945 in Morristown, New Jersey by the name of Lydia Susanna Hunter. She began her career at a young age as an actor and singer because her mother was a music teacher. She debuted in Hollywood in the 1980’s film version of Popeye as Mrs. Oxheart. She is currently known for her role as Hetty Lange on NCIS: Los Angeles. She has also stared in movies such as Pocahontas as Grandmother Willow, Mrs. Munion in Yours, Mine, and Ours, and Shadout Mapes in Dune. Throughout her career, she has won thirteen different awards, such as the 2012 Teen Choice Award for her character on NCIS: Los Angeles and an Oscar for “Best Actress in a Supporting Role” in 1984 for her movie The Year of Living Dangerously. She has happily lived with her partner, Karen Klein, since 1987. Not only is Linda Hunt an actress, but she also has Turner’s Syndrome.

Ethics and antenatal diagnosis?

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Three  copies  of  all  the  chromosomes:    triploidy  

There are 4 types of chromosome structural change – all of them associated with human disorders

Chromosome Structural Changes

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Reciprocal Translocations Mutual exchange of segments between two chromosomes, it is referred to as a reciprocal translocation.

46,XX,t(7;10)(q22;q24) Break and reunion occurred at bands 7q22 and 10q24. The segments distal to these bands were interchanged. The translocation event has not altered the total DNA content of this cell. Therefore, the translocation is microscopically (cytogenetically) balanced.

46,X,t(X;1)(p21;q32) Break and reunion occurred at bands Xp21 and 1q32. The segments distal to these bands were interchanged. The translocation is balanced. Note that the X chromosome is specified first.

46,XX,t(1;7;4)(q32;p15;q21) A complex translocation involving more than two chromosomes.

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Balanced reciprocal translocation

What is the ISCN karyotype?

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Balanced reciprocal translocation

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Balanced reciprocal translocation

46,XY,t(5;13)(p14.2;13q13.1)

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Unbalanced form of the reciprocal translocation

46XX,add(5)(p14)

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Unbalanced form of the reciprocal translocation

46,XX,del(13)(q13.1)

46,XX,der(13),t(5;13)(p14.2;q13.1)der pat

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Cri-du-Chat is Caused by the Loss of the Short Arm of One Copy of Chromosome 5

A Boy with Cri-du-Chat Syndrome – a Debilitating Disorder Caused by Chromosome Deletion

Mental and growth retardation, catlike cry in infancy, microcephaly, round face, hypertelorism, downslanting palpebral fissures

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