Exam 2: Medical Cytogenetics

Question 1

medical cytogenetics

Answer 1

field of inherited diseases based on chromosomal problems

Question 2

1/4 or more of miscarriages result…

Answer 2

from genetic diseases

Question 3

20% of all human conceptions…

Answer 3

have a major chromosomal abnormality

wrong # of chromosomes

structurally abnormal chromosomes

Question 4

haplotype

Answer 4

genotype of 1 chromosome

Question 5

karyotype

Answer 5

whole set of chromosomes

Question 6

aneuploidy

Answer 6

having the wrong # of chromosomes

gain or loss of one/several chromosomes

Question 7

are aneuploidies common?

Answer 7

at conception yes, but most are lethal causing spontaneous abortion

Question 8

almost all aneuploidies that survive involve…

Answer 8

chromosome 21, X, or Y

Question 9

disomy

Answer 9

having a pair of homologs (normal)

autosomes are normally disomic

Question 10

monosomy

Answer 10

having only 1 homolog

Question 11

trisomy

Answer 11

having 3 homologs

Question 12

does trisomy = triploidy?

Answer 12

no

Question 13

down syndrome

Answer 13

most common example of aneuploidy (trisomy 21)

1/700 to 1/800 births

Question 14

symptoms of down syndrome

Answer 14

many die from defects, some live over 50

extremely flexible joints, low muscle tone

link btw down and Alzheimer’s

Question 15

why chromosome 21?

Answer 15

smallest so aneuploidy causes least abnormality

300-400 genes

Question 16

what causes aneuploidy?

Answer 16

nondisjunction in mitosis or meiosis

Question 17

nondisjunction

Answer 17

leads to chromosome gain or loss in daughter cell

mitosis occurs in any dividing cell

meiotic can occur in meiosis I or II

Question 18

nondisjunction in meiosis I

Answer 18

MI: AABB + 0

MII: AB + AB + 0 + 0

Question 19

nondisjunction in meiosis II

Answer 19

MI: AA + BB

MII: AA + 0 + B + B

Question 20

determine origin of nondisjunction in Down syndrome

Answer 20

chromosome banding homologs can be distinguished

recognize which parental homologs caused trisomy

Question 21

what is the origin of nondisjunction in Down syndrome

Answer 21

80% due to nondisjunction in mom vs 20% in dad

Question 22

in female mammals meiosis begins in many _____ cells

Answer 22

germline

it goes as far as prophase I then stops in diplotene stage of prophase I

Question 23

eggs go through ______ at ovulation

Answer 23

metaphase I (1st polar body)

Question 24

eggs finish meiosis upon _____

Answer 24

fertilization

Question 25

female vulnerability to nondisjunction may be due to …..

Answer 25

long period of arrest in diplotene

why nondisjunction is mostly female and meiosis I

maternal age effect, but no paternal age effect

Question 26

trisomy 13, 18, 22

Answer 26

patau syndrome

edwards syndrome

over 30 cases reported

all 3 much more severe than Down

Question 27

general symptoms of autosomal aneuploids

Answer 27

developmental abnormality

mental retardation

lethal b4 birth

incurable at any stage of life

extreme, but variable in severity

Question 28

why is down the only common aneuploidy

Answer 28

they survive

smallest autosome (not proven)

Question 29

in aneuploidy 16…

Answer 29

30% of all cases but none survive to birth

Question 30

common sex chromosome aneuploidies

Answer 30

XXY klinefelter

XYY “XYY”

XXX “superfemale”

XO Turner syndrome

Question 31

is aneuploidy in sex chromosomes tolerated better than in autosomes?

Answer 31

yes

Y doesn’t code for much so extra copies don’t make a big difference

X has dosage compensation so extra X are inactivated

Question 32

effects of sex chromosome aneuploidies

Answer 32

variable

Question 33

sex nondisjunction MI (male)

Answer 33

MI: XXYY + 0

MII: XY + XY + 0 + 0

Question 34

sex nondisjunction MII (male)

Answer 34

MI: XX + YY

MII: XX + 0 + Y + Y OR X + X + 0 + YY

Question 35

sex nondisjunction MI (female)

Answer 35

MI: XXXX + O

MII: XX + XX + 0 + 0

Question 36

sex nondisjunction MII (female)

Answer 36

MI: XX + XX

MII: XX + 0 + X + X