Genetics Unit 4: Clinical Cytogenics 2

Front 1

Causes of Turner syndrome

Back 1

1) 45,X [50%]
2) Structural abnormality in one X (ring X, isochromosome X, Deletion) [15%]
3) 45,X 46XX mosaicism [15%]
4) Other mosaicisim [15%]

Front 2

Mitotic Nondisjunction

Back 2

During mitosis, when one daughter cell gets both chromatids and the other daughter gets none. This leads to mosaicism in which cells could have 45,46, or 47 chromosomes (depending if the 45 and 47 are viable)

Front 3

Mitotic Anaphase lagging

Back 3

One of 2 chromatids may lag behind in anaphase and get lost. This leads to mosaicism with some cells having 46 chromosomes and some 45.

Front 4

Somatic Recombination

Back 4

An exchange of segments between homologous chromosomes. May lead to homozygosity at gene loci that are heterozygous in all other daughter cells. Extremely rare. Important step in some cancers.

Front 5

Frequency of nondisjunction in all conceptions and parental origin

Back 5

7%. 94% of maternal origin. Dramatically increases in women in 30s - 40s.

Front 6

Aneuploidy

Back 6

Non-disjuction occuring in mieosis 1 or 2. Leads to monosomy or trisomy.

Front 7

Triploidy and mechs of formation

Back 7

Have 69 chromosomes. Very few liveborn. Occurs via:
1) Dispermy - Haploid egg + 2 haploid sperm (most common)
2) Diploid egg + Haploid sperm
3) Haploid egg + Diploid sperm

Front 8

Terminal Deletion

Back 8

A single break in a chromosomal arm at end of chromosome. Most common is deletion of 5p of cri du chat syndrome

Front 9

Interstital Deletion

Back 9

2 Breaks occur within same arm, middle segment is lost, and outer segments reattach. Most common is at 15q and produces Prader-Willi syndrome

Front 10

Paracentric inversion

Back 10

2 breaks occur on same arm, middle segment inverts, and reattaches. Phenotype is normal but can have a reduced fertility. Cross over causes a loop creating dicentric and acentric products. Dicentric and acentricc cross over products are not usually viable.

Front 11

Pericentric Inversion

Back 11

2 breaks in 2 different arms occur, middle segments switch and reattach. No phenotypic problems but reduced fertility. Inversion loop is formed during crossing over. High risk of abortions and abnormal liveborns.

Front 12

Reciprocal Translocation

Back 12

If part of chromosome A goes to B and B goes to A and no genetic material is lost. No phenotypic problems but increases risk of spontaneous abortion or abnormal children.

Front 13

Robertsonian Translocation

Back 13

A break occurs in the short arm of 2 acrocentric chromosomes and the centromeres fuse. B/c short arms of acrocentric chromosomes are just repeats of DNA, no phenotypical consequences. Does significantly increase risk of trisomy 21. 14/21 is most common.

Front 14

Uniparental Disomy

Back 14

The cell is diploid but two homologues of a chromosome come from the same parent. Can be caused by:
A trisomic conception that loses one of the extra chromosomes.
A monosomy conception undergoing a mitotic non-disjunction.

Front 15

Isodisomy

Back 15

Uniparental Disomy where 2 homologues are derived from one copy of parental chromosome.

Front 16

Heterodisomy

Back 16

Uniparental disomy where 2 homologous chromosomes are derived from 2 copies of a parental chromosome.

Front 17

Imprinting Effect

Back 17

Where two diseases have the same deletions but different symptoms based on whether the incorrect genetic material is from the maternal or paternal chromosome.

Front 18

What are more common; partial or whole chromosome abnormalities?

Back 18

Partial (except for trisomy 21)

Front 19

If there is nondisjunction at Meiosis 1, what is the final outcome?

Back 19

2 cells with 24 chromosomes, 2 with 22.

Front 20

If there is nondisjunction at Meiosis 2, what is the final outcome?

Back 20

2 cells with 23 (normal) chromosomes, one with 22, and one with 24

Front 21

If trisomy is present, how can you tell whether a non disjunction occurred at Meiosis 1 or 2?

Back 21

If Meiosis, the 2 copies from the same parent will be different. If meiosis 2, they will be the same.

Front 22

Outcomes for people with a pericentric inversion V.S. Paracentric

Back 22

Parasentric inversion offspring are either normal, or do not survive because the other products are not viable.
Pericentric have a high percent chance to have an offspring which is viable but not normal.

Front 23

Alternate segregation in meiosis of a reciprocal translocation carrier.

Back 23

One daughter gets both normal chromosomes, one daughter gets both translocated, therefore both cells have all the genetic material. Half of zygotes will be completely normal, half will be carriers of translocation like parent.

Front 24

Adjacent-1 Segregation in meiosis of a reciprocal translocation carrier.

Back 24

Both daughter cells have one normal chromosome, and one chromosome with missing and extra genetic material. All offspring will be abnormal or will not be conceived b/c lack a piece of genetic material and have a copy of a piece of genetic material. (Partial trisomy, Partial monosomy)

Front 25

Adjacent-2 Segregation in meiosis of a reciprocal translocation carrier.

Back 25

Both daughters receive 2 of the same chromosome and none of the other except for the small translocated portions. Almost always a miscarriage b/c almost entire chromosome is missing and almost entire chromosome is duplicated. (Partial trisomy, partial monosomy)