Lecture 22-Cytogenetics 1

Question 1

Euchromatin is largely composed of ______ sequences vs. heterochromatin which is largely composed of _______ sequences.

Answer 1

• coding

- non-coding

Question 2

Heterochromatin is largely found where?

Answer 2

• centromeres

- distal end of Y

Question 3

Each centromere has how many bps?

Answer 3

171

Question 4

Are all centromeres the same?

Answer 4

no, they can differ from chromosome to chromosome

Question 5

Chromosomes 13, 14, 15, 21, 22 all have what structure?

Answer 5

acrocentric

Question 6

Describe an acrocentric chromosome.

Answer 6

• no euchromatin on P arm
• has many repeats of rRNA genes so it can be very large or non-existant
• these genes are redundant among acrocentric chromosomes

Question 7

If someone has trisomy they have ____ chromosomes.

Answer 7

47

Question 8

If someone has monosomy they have ____ chromosomes.

Answer 8

45

Question 9

What are 3 ways to get cells from a fetus in order of lowest to highest rate of miscarriage?

Answer 9

• amniocentesis
• CVS
• PUBS (percutaneous umbilical blood sample)

Question 10

When is peripheral blood not used for diagnosis of congenital abnormalities?

Answer 10

• PUBS

- Acquired abnormalities like leukemia

Question 11

Phytohemagglutinin (PHA)

Answer 11

mitogen to stimulate WBCs in peripheral blood to divide so they can get to metaphase for analysis

Question 12

What is bone marrow tissue used for with respect to diagnostic testing?

Answer 12

leukemia

Question 13

When is a skin biopsy usually used? What is it’s caveat?

Answer 13

• to compare karyotypes between skin and blood

- takes a long time to growth them in culture and therefore before preparation can be done

Question 14

If you draw someones blood you could expect their WBCs to be in what phase?

Answer 14

• G0

Question 15

What are the chromatid counts (per chromosome) at the end of each phase of the cell cycle?

Answer 15

• G1: 1
• S: 2
• G2: 2
• M: 1

Question 16

What happens during prometahpase?

Answer 16

nuclear envelope disappears

Question 17

What is the difference between the nuclear spindle attachments between prophase and prophase I?

Answer 17

• prophase: one chromosome/spindle

- prophase I: homologous chromosomes/spindle

Question 18

colcemid

Answer 18

spindle fiber poison that freezes cells in metaphase

Question 19

What do you need to do with cell samples prior to Giemsa staining?

Answer 19

• trypsin digest of some chromosomal proteins

Question 20

When does independent assortment take place?

Answer 20

• meiosis 1

Question 21

reduction division

Answer 21

• occurs during meiosis 1

- is the halving of chromosomes from 46–>23

Question 22

What is the law of independent assortment?

Answer 22

largely maternal chromosomes and largely paternal chromosomes can be grouped together in the same gamete

Question 23

At least 1 _____ is required for regular orientation of the chromosomes on the spindle during meiosis I.

Answer 23

chiasma

Question 24

Other than mixing of genes, chiasmata do what?

Answer 24

• stabilize chromosomes on the spindles and decrease the risk of nondisjunction

Question 25

Where are chiasmata not seen?

Answer 25

on acrocentric chromosomes

Question 26

How do the number of meiotic divisions differ between males and females?

Answer 26

men have more divisions that are subdivisions of prophase 1. This is where crossing over occurs

Question 27

Female gamete synthesis stops where first? When does it resume?

Answer 27

- prophase 1, resumes in the 1st half of the menstrual cycle | - meiosis completes at fertilization

Question 28

What is the difference in outcomes of meiosis in females vs. males?

Answer 28

- females have 1 gamete made/meiosis | - males make 4/meiosis

Question 29

Constitutional abnormalities (cytogenic abnormalities present at CONCEPTION) are associated with ____ (2)

Answer 29

- birth defects | - miscarriages

Question 30

What is the most common and clinically significant type of chromosome disorder? What is it's frequency?

Answer 30

- aneuploidy | - 3-4%

Question 31

How does aneuploidy arise?

Answer 31

- nondisjunction

Question 32

How can you tell which parent gave the aneuploidy in trisomies?

Answer 32

- you can't tell

Question 33

Majority of aneuploidies are from _____, when?

Answer 33

the mom during meiosis 1, nondisjunction is more common in females

Question 34

Downs syndrome accounts for what percent of chromosomal abnormalities at birth?

Answer 34

50%

Question 35

Kids with downs are at increased risks for what 2 things?

Answer 35

- leukemias | - congenital heart defects

Question 36

Do you need 47 chromosomes to have a trisomy 21?

Answer 36

no, you can have a translocation so the third copy of 21 is attached to another chromosome

Question 37

Describe the viability of Trisomy 18 and 13.

Answer 37

- 5% live to 1 year old

Question 38

Which trisomy is associated with midline defects?

Answer 38

- Trisomy 13

Question 39

What are the phenotypes associated with autosomal abnormalities? (4)

Answer 39

- developmental delay/MR - facial features more characteristic fo the syndrom than of family members - growth delay - congenital malformations

Question 40

Why do the phenotypes associated with sex chromosome abnormalities tend to be milder than autosomal abnormalities?

Answer 40

- fewer genes on sex chromosomes and most have to do sex development

Question 41

Which sex chromosome abnormalities do not result in infertility? Are they pretty harmful to those affected?

Answer 41

- XXX, XYY | - fairly benign: just the typical abnormal heigh, lower IQ

Question 42

What can aberrant crossover between sex chromosomes cause? How?

Answer 42

- sex reversal: if the SRY gene gets translocated it results in sex reversal