Lecture 23-Cytogenetics 2

Question 1

Robertsonian translocation

Answer 1

• exchange between whole arms of acrocentric chromosomes

Question 1

With a balanced Robertsonian translocation how many chromosomes are you left with? Why?

Answer 1

• 45: you lose the acentric arm material

Question 2

With an unbalanced Robertsonian translocation how many chromosomes are you left with?

Answer 2

• 46

Question 3

Why are people with trisomies from translocations worrisome?

Answer 3

• they can pass on the abnormal chromosome to their offspring

Question 4

(T/F) People with Robertsonian translocations can have normal or non-normal children.

Answer 4

True. They are just subject to having more miscarriages due to monosomic zygotes

Question 5

what is the most common robertsonian translocation?

Answer 5

13:14. 21 is also a fairly common participant

Question 6

Recriprocal translocations

Answer 6

• non-robertsonian translocation

Question 7

With an unbalanced reciprocal translocation how many chromosomes are you left with?

Answer 7

46

Question 8

With an balanced reciprocal translocation how many chromosomes are you left with?

Answer 8

46, very rarely 47

Question 9

Although balanced translocations maintain the same amount of genetic material, they cause an increased likelihood of ______

Answer 9

miscarriages

Question 10

what is a partial trisomy? partial monosomy?

Answer 10

• when only part of a chromosome is duplicated into a third copy
• when there is one full chromosome and only part of it’s homologous chromosome

Question 11

What type of translocation carrier can potentially give rise to all types of children (unbalanced carrier, balanced carrier, unaffected)

Answer 11

someone with a balanced translocation

Question 12

Inheritance of a familial translocation where carriers are phenotypically normal should result in what kind of phenotype?

Answer 12

• normal

Question 13

De novo mutation carriers have a ___% risk of unknown phenotypic abnormalities.

Answer 13

• 10%

Question 14

What will happen to conceptuses with small chromosomal imbalances? Large?

Answer 14

• small: viable but abnormal

- large: abort

Question 15

What are the 3 types of deletions?

Answer 15

• terminal
• interstitial
• ring

Question 16

What is the problem with a ring deletion?

Answer 16

• doesn’t go through mitosis well there are more problems than would be expected if just the ends were deleted but the ring structure hadn’t formed

Question 17

Microdeletion

Answer 17

• <5Mb deletion which can be missed by G-band studies

Question 18

What are 4 examples of microdeletion syndroms?

Answer 18

• Prader-Willi/Angelman
• Rb
• William
• DiGeorge/Velocardiofacial

Question 19

How can you detect microdeletion syndromes? (3)

Answer 19

• high resolution chromosome analysis
• FISH
• CGH array

Question 20

Isochromosome

Answer 20

When sister chromatids separate incorrectly and you’re left with 2 q or 2 p arms on one chromosome

Question 21

Isochromosomes are seen in what syndrome?

Answer 21

Turners

Question 22

Pericentric inversion

Answer 22

• around centromere

- balanced rearrangement

Question 23

What is the abnormal recombinant of a pericentric inversion?

Answer 23

• duplication of the p arm and deletion of the q arm

Question 24

Paracentric inversion

Answer 24

- genes stay within p or q arms, and centromere not involved

Question 25

What is the abnormal recombinant in a paracentric inversion?

Answer 25

- either 2 centromeres (doesn't fare well during mitosis) - no centromeres (gets lost during mitosis) - almost never viable

Question 26

What does having a parent with an inversion mean for their potential offspring?

Answer 26

- higher risk of having a duplication and deletion of parts of chromosome involved

Question 27

Mosaicism

Answer 27

- presence in an individual or a tissue of at least two cell lines which differ karyotypically by are from a single zygote. Ex: some cells are trisomy 21 and some aren't - can result from nondisjunction

Question 28

Severity of phenotype in mosaicism depends on _____(2).

Answer 28

- tissue distribution of the abnormal cell line | - frequency of the abnormal cell line

Question 29

Mosaicism can be beneficial when _____

Answer 29

- it results in trisomy rescue. When someone with trisomy from a meiotic nondisjunction has anaphase lag resulting in a normal cell, although, this normal cell would be the minority

Question 30

Confined placental mosaicism | - when did we start seeing this?

Answer 30

- discrepancy between placental and fetal karyotype that can lead to false negatives or false positives for trisomies - after the advent of CVS

Question 31

~20% of the pregnancies with _______ have confined placental mosaicism.

Answer 31

- idiopathic intrauterine growth retardation (small body)

Question 32

Uniparental disomy (UPD)

Answer 32

- disomic cell line containing 2 chromosomes inherited from only one parent - usually the result of nondisjunction

Question 33

Why are UPDs dangerous?

Answer 33

- because maternal and paternal DNA's imprinting patterns are different

Question 34

Genomic imprinting involves modification of DNA during a critical period which can _____.

Answer 34

- influence the expression of human genetic disorders and temporarily change gene expression contrary to mendelian principles

Question 35

What is the difference between Prader-Willi and Angelman's syndrome? What are other ways we can get either of these syndromes.

Answer 35

- PWS: is an interstitial deletion in the father's chromosome 15 so there are 2 MATERNAL CHROMOSOMES - AS: Interstitial deletion in the mother's chromosome 15 so there are 2 PATERNAL CHROMOSOME 15s - you can also get both of these by UPD

Question 36

CGH can detect what? what can't it detect?

Answer 36

- submicroscopic abnormalities down to individual bps | - cant tell you about balanced structural abnormalities which is fine because the concern is unbalanced translocations

Question 37

CMA is another name for _____

Answer 37

CGH