Lecture 5: Intro to Cytogenetics

Question 1

What proportion of conceptuses have xs anomaly? What proportion are born live?

Answer 1

1/13

6/1000

Question 2

what percent of recognized pregnancies end in spontaneus abortion? What percent of these are in the first tirmester?

Answer 2

15%

80%

Question 3

what percent of spontaneous abortions are chromosomal? what percent of these are trisomies?

Answer 3

60%

52%

Question 4

what percent of newborns have a xs anomaly?

Answer 4

0.6%

Question 5

what specimen are used for cytogenic analysis?

Answer 5

blood, amniotic fluid, chorionic villi, bone marrow, tissue

Question 6

in what phase are chromosomes arrested for cytogenic analysis

Answer 6

metaphase

Question 7

Where is the sequence TTAGGG found?

Answer 7

telomeres

Question 8

what are xs polymorphisms?

Answer 8

normal variation - presence of two or more alternative structural forms for a xs within a population - benign

Question 9

what is euploidy?

Answer 9

exact multiples of the haploid set (N 2N 3N 4N)

Question 10

what is aneuploidy?

Answer 10

gain or loss of chromosomes equalling less than one complete complement

Question 11

From what does aneuploidy result?

Answer 11

meiotic and mitotic nondisjunction errors

Question 12

is aneuploidy inherited?

Answer 12

usually not

Question 13

is mosaicism inherited?

Answer 13

No!

Question 14

what is mosaicism?

Answer 14

mutation which leads to a unique second cell, which establishes a second cell line

Question 15

how do mosaics and chimeras differ?

Answer 15

mosaic: mutation which leads to a unique second cell, which establishes a second cell line\
chimera: cell lines have many differences which can be traced back to the original two cells

Question 16

what results from trisomy 21?

Answer 16

down syndrome

Question 17

what results from trisomy 13?

Answer 17

patau syndrome

Question 18

what results from trisomy 18?

Answer 18

Edwards syndrome

Question 19

how do sex xs aneuploidies differ from autosomal aneuploidies?

Answer 19

sex are usually milder, more common

Question 20

what are symptoms of patau syndrome?

Answer 20

failure to thrive, cleft lip, rocker bottom feet, polydactyly, punched out scalp, small head, heart defect

Question 21

what are symptoms of edwards syndrome?

Answer 21

low birth weight, small mouth/jaw, ventricular septal defect, hypoplasia of muscles, prominent occiput, low-set malformed ears, rockerbottom feet, CROSSED FINGERS

Question 22

How is turner syndrome characterized?

Answer 22

45,X

Question 23

What is the region of the sex chromosomes that engages in recombination?

Answer 23

Pseudoautosomal region

Question 24

which sex development is default?

Answer 24

female

Question 25

what must be present for male development to occur?

Answer 25

TDF (testes determining factor)

SRY (sex determining region of Y)

Question 26

If TDF/SRY are ABSENT, what will happen?

Answer 26

ovaries develop
Mullerian ducts differentiate –> internal female reproductive organs
Wolffian ducts regress

Question 27

If TDF/SRY are present and ACTIVE, what will happen?

Answer 27

testes develop –> inhibition of Mullerian ducts

androgen is produced –> stimulates proliferation of Wolffian ducts

Question 28

Once the sex of an individual has been determined, what will happen with gain or loss of key genes/a sex xs?

Answer 28

nothing

Question 29

what chromosomes determine sex?

Answer 29

X, Y, and autosomes

Question 30

what does dosage compensation come from?

Answer 30

X inactivation

Question 31

what is somatic mosaicism?

Answer 31

if a female is heterozygous for a trait on the X chromosome, some cells will express the paternal trait and some will express the maternal trait

Question 32

what is non-random X inactivation?

Answer 32

damaged X is preferentially inactivated

Question 33

what is an example of somatic mosaicism?

Answer 33

calico cat

Question 34

are any calico cats male?

Answer 34

no

Question 35

how does X inactivation occur (what modification is used)?

Answer 35

methylation of one X xs
NO gene mutations
Epigenetic modification

Question 36

when must an inactive X be reactivated?

Answer 36

meiosis - pass along to gametes

Question 37

what region escapes X inactivation?

Answer 37

pseudoautosomal region