Numerical Chromosomal Abnormalities I

Question 1

the chromosome content is reduced from __ to __ in the first meiotic division, and from __ to __ in the second meiotic division, where n is the euploid number of chromosomes

Answer 1

4n
2n
2n
n

Question 2

Two key differences between mitosis and meiosis are that

Answer 2

1) paternally- and maternally-derived homologous chromosomes pair at the onset of meiosis (prophase I), whereas the two homologs segregate independently in mitosis
2) reciprocal recombination events between maternal and paternal sister chromatids generate chiasmata (physical linkages) between homologs in meiosis; in contrast, recombination between homologs is rare during mitosis

Question 3

Meiotic prophase I

Answer 3

• Maternal and paternal homologs of each chromosome become paired, forming “bivalents”
• Formation of the synaptonemal complex
• Reciprocal recombination events occurring at this stage generate chiasmata
• On average, 2-3 crossovers occur on each chromosome, resulting in genetic reassortment between chromosomes.
• The synaptonemal complex disassembles at the end of prophase I
• Bivalents are therefore held together only by chiasmata.

Question 4

Formation of bivalents requires

Answer 4

the formation of a proteinaceous structure called the synaptonemal complex, which promotes inter-homolog interactions

Question 5

Chiasmata

Answer 5

physical crossover links between homologs

Question 6

Bivalents

Answer 6

structures formed when homologs of each chromosome become paired or synapsed along their entire lengths

Question 7

__________ is the most error-prone step of the process, and chromosome nondisjunction at this stage is the most frequent mutational mechanism in humans

Answer 7

Meiosis I

Question 8

Meiosis I is the most error-prone step of the process, and __________ at this stage is the most frequent mutational mechanism in humans

Answer 8

chromosome nondisjunction

Question 9

Meiosis II is very much like a __________ division

Answer 9

mitotic

Question 10

chromosomes undergo a second round of __________ in meiosis II without an intervening round of __________

Answer 10

segregation

DNA replication

Question 11

Genetic consequences of meiosis (3)

Answer 11

A. reduction in chromosome number from diploid to haploid
B. random segregation of homologous chromosomes, giving ~8x106 (or 223 ; 2 homologs for each of 23 chromosomes) different possibilities
C. random shuffling of genetic material due to crossover events, resulting in a vast increase in genetic variability from the above estimate

Question 12

Mitosis (6)

Answer 12

A. one round of chromosome segregation, resulting in daughter cells identical in chromosomal content to the parental cell
B. DNA replication precedes each round of chromosome segregation
C. no pairing of homologous chromosomes
D. infrequent recombination
E. centromeres on paired sister chromatids segregate at each anaphase
F. occurs in somatic cells and in germ line precursor cells prior to entry into meiosis

Question 13

Meiosis (5)

Answer 13

A. two rounds of chromosome segregation without an intervening round of DNA replication
B. parental cells must be diploid and the chromosome number is halved in the resultant cells
C. requires the pairing of homologous chromosomes and recombination for its successful completion
D. centromeres on paired sister chromatids divide only at anaphase II in a normal meiosis
E. occurs only in the germ line

Question 14

Metacentric

Answer 14

the centromere is located in the middle of the chromosome, such that the two chromosome arms are approximately equal in length

Question 15

Submetacentric

Answer 15

the centromere is slightly removed from the center

Question 16

Acrocentric

Answer 16

the centromere is near one end of the chromosome

Question 17

Chromosomes are also classified __________ based on banding patterns observed microscopically after treatment with stains such as Giemsa, quinocrine, DAPI (4’,6-diamino-2-phenylindole), Hoechts, etc

Answer 17

cytogenetically

Question 18

Short arm locations are labeled _ and long arms are labeled _

Answer 18

p (petite)

q

Question 19

Each chromosome is considered to be divided into different regions labeled p1, p2, p3; q1, q2, q3 etc., counting __________ from the centromere

Answer 19

outwards

Question 20

Chromosomal regions are defined by specific landmarks (distinct morphological features) that include __________, __________, and __________

Answer 20

telomeres, centromeres, and banding patterns

Question 21

How do you read p11.1?

Answer 21

P one-one point one

Question 22

How do you name chromosome based on their proximity to the centromere?

Answer 22

proximal or distal

Question 23

What type of numerical abnormality? 69,XXX; 69 XXY; 69,XYY

Answer 23

Triploidy

Question 24

What type of numerical abnormality? 47,XX,+21

Answer 24

Trisomy

Question 25

What type of numerical abnormality? 45,X

Answer 25

Monosomy

Question 26

What type of numerical abnormality? 47,XXX/46,XX

Answer 26

Mosaicism

Question 27

What type of structural abnormality? 46,XY,del(4)(p16.3) and 46,XX,del(5)(q13q33)a

Answer 27

Deletion

Question 28

What type of structural abnormality? 46,XY,inv(11)(p11p15)

Answer 28

Inversion

Question 29

What type of structural abnormality? 46,XX,dup(1)(q22q25)

Answer 29

Duplication

Question 30

What type of structural abnormality? . 46,XX,ins(2)(p13q21q31)b

Answer 30

Insertion

Question 31

What type of structural abnormality? 46,XY,r(7)(p22q36)

Answer 31

Ring

Question 32

What type of structural abnormality? 46,XX,+marc

Answer 32

Marker

Question 33

What type of structural abnormality? 46,XY,t(2;6)(q35;p21.3)d

Answer 33

Translocation, reciprocal

Question 34

What type of structural abnormality? 45,XY,der(14;21)(q10;q10)e and 46,XX,der(14;21)(q10;q10),+21f

Answer 34

Translocation, Robertsonian