Numerical Chromosomal Abnormalities

Question 0

Chromosomal abnormalities occurring during mitosis result in what type of mutation?

Answer 0

Cause mosaicism
Somatic mutations
Germ line mutations if they arise in germ line predecessors

Question 1

Chromosomal abnormalities occurring during meiosis result in what type of mutations?

Answer 1

Germ line mutations

Question 2

What is the synaptonemal complex?

Answer 2

Proteins that link the homologous chromosomes to each other during crossover

Question 3

Homologous chromosomes separate during which meiotic division?

Answer 3

Meiosis I

Question 4

Sister chromatids separate during which meiotic division?

Answer 4

Meiosis II

Question 5

Female gametes are arrested in which stage until ovulation?

Answer 5

Meiosis I

Question 6

What are chiasmata and what critical role to they play?

Answer 6

Chiasmata are the points of connection between homologous chromosomes during crossing over.
This physical link is critical for normal chromosomal disjunction.

Question 7

Two processes that result in genetic variability between gametes.

Answer 7

Independent assortment of parental chromosomes. ~8x10^6
Crossing over of homologous chromosomes.
Approximate number of possible variants ~80^23

Question 8

What is the ploidy of normal somatic cells during G2?

Answer 8

2n

Question 9

What is the ploidy of normal gametes after meiosis I?

Answer 9

2n

Question 10

A non disjunction during what phase of meiosis results in 100% abnormal cells?

Answer 10

Meiosis I

Question 11

A non disjunction during what phase of meiosis results in 50% abnormal cells?

Answer 11

Meiosis II

Question 12

What do Gimsa dark regions in a chromosome indicate?

Answer 12

High concentrations of A-T pairs

Question 13

What do p and q signify?

Answer 13

p denotes loci on the short (petite) arm of a chromosome

q denotes loci on the long arm of a chromosome

Question 14

What is the difference between daughter and mother cells in mitosis and meiosis?

Answer 14

In mitosis, the daughter and mother cells are genetically identical.
In meiosis, the daughter cells have wide genetic variation from the mother cells and 1/2 the total chromosomes (n vs. 2n)

Question 15

What is G-Banding?

Answer 15

The resulting striated coloration of chromosomes after dyeing with Gimsa dye.

Question 16

What are the three classifications of chromosomes, based on centromere location?

Answer 16

Metacentric - centered centromere approximately equal p & q lengths
Sub-metacentric - off-center centromere
Acrocentric - centromere nearly at end of chromosome, only stalk and satellite region beyond it

Question 17

How are genetic abnormalities denoted in short hand?

Answer 17

Total number of chromosomes
Sex chromosomes
Abnormality type
Chromosome on which the abnormality occurs
Specific locus of abnormality (p/q numbers)

Question 18

Extra copies of all chromosomes is termed:

Answer 18

Polyploidy

E.g.: triploidy (3n), tetraploidy (4n)

Question 19

Gain or loss of one chromosome is termed:

Answer 19

Aneuploidy

E.g.: Trisomy 2, monosomy X

Question 20

What is the most commonly occurring pathway that results in triploidy?

Answer 20

Dispermy - simultaneous fertilization of the egg by two sperm or by a single 2n sperm

Question 21

What is the most commonly occurring pathway that results in tetraploidy?

Answer 21

Endomitosis, wherein the cell undergoes DNA replication, but fails to separate the replicated strands during cell division.

Question 22

In mothers over age 35, what is the frequency of abnormal chromosomes in fetuses, and what percentage of those abnormalities are numerical?

Answer 22

1:50 fetuses have abnormal chromosomes.

85% are numerical abnormalities.

Question 23

What is the most common mechanism leading to aneuploidy?

Answer 23

Meiotic chromosome nondisjunction

Question 24

Aberrations in the frequency or location, or both, of recombination events in meiosis I are associated with what?

Answer 24

Increased rates of meiosis I non disjunction

Question 25

What does "terminalization" refer to?

Answer 25

The loss of cohesion between homologous chromosomes and the movement of chiasmata to the ends of the chromosomes. Causes precocious separation of chromosomes, known as meiosis I nondisjunction.

Question 26

Trisomy 21 name, incidence & characteristics.

Answer 26

Down Syndrome 1/830 live births Intellectual disabilities, characteristic features, short stature, gastrointestinal abnormalities, early onset Alzheimer's

Question 27

Trisomy 13 name, incidence, and characteristics.

Answer 27

Patau syndrome 1/22700 CNS abnormalities, facial clefts, renal hyperplasia, congenital heart disease

Question 28

Trisomy 18 name, incidence, and characteristics.

Answer 28

Edwards syndrome 1/7500 Hypertonicity, CNS abnormalities, growth retardation, congenital heart disease

Question 29

What is the overall incidence of trisomy disorders in live births?

Answer 29

Approximately 1:700

Question 30

Why are phenotypes associated with sex chromosome aneuploidy often less severe than those associated with autosomal aneuploidy?

Answer 30

Due to X chromosome inactivation and the relatively low number of genes that reside on the Y chromosome.

Question 31

Defects in sex chromosome number can often be traced to what common factor?

Answer 31

Errors in maternal meiosis as a result of increased maternal age.

Question 32

Klinefelter Syndrome abbreviation, incidence, and common cause.

Answer 32

(47, XXY) 1:1000 live male births 50% from errors in MALE meiosis I due to failure of recombination in pseudoautosomal regions 15% result from mosaicism, commonly (46, XY/47, XXY)

Question 33

47, XYY syndrome incidence, characteristics, and cause.

Answer 33

Incidence is 1:1000 live male births Caused by paternal meiosis II errors, producing YY sperm Indistinguishable physically or mentally from unaffected males, increased risk of behavioral and educational problems, delayed language ability

Question 34

Turner syndrome abbreviation, incidence, characteristics and cause.

Answer 34

45, X 1:4000 live female births, 25% mosaic >99% abort spontaneously Short stature, webbed neck, edema of hands and feet, renal and cardiovascular anomalies

Question 35

What is mosaicism and what causes it?

Answer 35

Mosaicism is the presence of two or more chromosome compliments within one individual (ie. some cells 46, XY/ others 47,XY,+21) Commonly caused by nondisjunction in an early post-zygotic mitotic division.

Question 36

What are the two types of mosaicism?

Answer 36

Polyploidy (2n/4n) | Aneuploidy (normal/trisomy 21)