Chromosome Abnormalities

Question 1

What percentage of trisomy 21 cases arise from meiosis nondisjunction

Answer 1

95%

Question 2

Monosomic

Answer 2

Zygote or diploid cell that is missing a chromosome 2n-1

Question 3

Trisomic

Answer 3

Zygote or diploid cell that has an extra chromosome 2n+1

Question 4

Polyploidy

Answer 4

Extra set of total haploid genome

Question 5

Nullsomic

Answer 5

Haploid cell or gamete that is missing an chromosome n-1

Question 6

Disomic

Answer 6

Haploid cell or gamete that has an extra chromosome

Question 7

What are common mechanisms for the arisal anueploidy

Answer 7

Chromosome NDJ or loss of chromosome during cell division

Question 8

Sporadic Aneuploidies

Answer 8

Most common and caused by mutations

Question 9

Hereditary Aneuploidies

Answer 9

Less common, but the mutation is present in the Germline and can be transmitted to the offspring

Question 10

Meiotic NDJ

Answer 10

Improper segregation of chromosomes during meiosis with either homologous or sister chromatids

Question 11

Mitotic NDJ

Answer 11

Failure of sister chromatids to migrate to opposite poles during anaphase

Question 12

Mosaicism

Answer 12

Presence of two or more cell lines of different genetic or chromosomal constitution

Question 13

Trisomy 21 Mosaicism

Answer 13

NDJ occurs in the second division after zygote formation

Question 14

Primary NDJ

Answer 14

NDJj occurs at a low frequency in cells with normal chromosome numbers

Question 15

Secondary NDJ

Answer 15

NDJ occurs at a higher frequency in Aneuploid cells

Question 16

X polysomies (XXX/XXY)

Answer 16

Better tolerated than autosomal polysomies

Question 17

Why are Y chromosome deficiencies/surpluses better tolerated than autosomal

Answer 17

Y chromosome is largely heterochromatic

Question 18

What happens when there are autosomal monosomies

Answer 18

Death

Question 19

Which autosomal trisomies are survivable

Answer 19

13,18, 21 because they are small

Question 20

What is hereditary Down syndrome

Answer 20

The aberrant chromosome exists in the parents gametes and is transmitted to the offspring

Occurs bc of a Robertsonian translocation or by an isochromosome 21

Question 21

What percentage of trisomy 21 cases are because of mosaics

Answer 21

2-4% and the germ cells would be Trisomic leading to the transmission to half of the children

Question 22

Which parental lineage are most trisomy 21 cases attributed to

Answer 22

Maternal origin
MI errors=80%
MII errors=20%

Question 23

What is the age cut off where bearing children yields a spike in potential trisomies

Answer 23

35 years young

Question 24

Contiguous gene syndrome

Answer 24

Syndrome resulting from the deletion of a segment of DNA containing portions from multiple adjacent genes
Multiple genes lose their function

Question 25

What is the max survivability of trisomy 13

Answer 25

6 months

Associated with advanced maternal age and NDJ in MI

Question 26

Max survivability of trisomy 18

Answer 26

A few months max

Advanced maternal age is a factor

Question 27

What is a characteristic sign of trisomy 18

Answer 27

Clenched fist with digits 2/5 over 3/4

Question 28

NDJ during MI results in what

Answer 28

2o oocyte and 1st polar body a well as both 2o spermatocytes to be Aneuploid

Question 29

NDJ during MII results in what

Answer 29

2 or 4 meiosis products affected