Chromosomal Abnormalities

Question 1

What’s an acrosome?

Answer 1

where the p arm is much shorter than the q (long) arm, with repeating rRNA sequences

Question 2

What does improper repair of chromosome breaks result in?

Answer 2

structural abnormalities

Question 3

What is needed for a stable chromosome?

Answer 3

one centromere and two terminal telomeres

Question 4

What is a Robertsonian translocation?

Answer 4

long-arm fusion and short arm loss of acrocentric chromosomes; balanced because all the genetic info is still just fused

Question 5

What is a balanced translocation?

Answer 5

contains the net normal amount of genetic material; normal phenotype but with reproductive risk

Question 6

Unbalanced translocation

Answer 6

rearrangement with missing or extra material; high likelihood of phenotypic abnormality

Question 7

What is a reciprocal translocation?

Answer 7

simple exchange of a chromosome segment with another chromosome; balanced category of rearrangement

Question 8

What is the risk for a balance translocated parent’s offspring?

Answer 8

risk of unbalanced gamete which would see either partial trisomy or partial monosomy in the conceptus

Question 9

What is partial trisomy/monosomy?

Answer 9

three copies or one copy of a gene on a chromosome = unbalanced

Question 10

How can someone with a Roberstonian translocation be phenotypically normal?

Answer 10

the short arm that got lost can be redundant material

Question 11

What is the reproductive risk of a Robertsonian carrier?

Answer 11

have 3 instead of 4 chromosomes for segregation into 2 daughter cells

Question 12

Is deletion un/balanced? any type of polysomy?

Answer 12

unbalanced because material is lost; partial monosomy for deleted segment

Question 13

What is the basis for Wolf-Hirschhorn syndrome?

Answer 13

deletion on chromosome 4

Question 14

Is isochromosome un/balanced? any type of polysomy?

Answer 14

unbalanced because it’s a centromere misdivision where you get p-p arms and q-q arms; both partial trisomy and monosomy

Question 15

Is duplication un/balanced? any type of polysomy?

Answer 15

unbalanced (extra material); partial trisomy

Question 16

Is inversion un/balanced? any type of polysomy?

Answer 16

balanced because the segment just gets turned around; no polysomies

Question 17

What is the difference between paracentric inversion and pericentric inversion?

Answer 17

centromere involved in inverted segment in the pericentric inversion

Question 18

Ring chromosome

Answer 18

2 breaks, 1 break at each end; terminal acentric fragment is lost and repair is joining the ends together to form a ring

Question 19

Is a ring chromosome un/balanced? any type of polysomy?

Answer 19

unbalanced and partial monosomy for both lost terminal fragments

Question 20

Who has a higher risk of passing on Robertsonian translocation: mother or father, and why?

Answer 20

maternal risk is 1–fold higher because chromosome segregation is riskier in eggs

Question 21

Which chromosomal abnormalities are most lethal?

Answer 21

autosomal trisomies or monsomies

Question 22

What is homologous Robertsonian translocation?

Answer 22

two copies of the same acrocentric long arm; only option is monosomy or trisomy, no chance for balances

Question 23

What is the chromosome number for a balanced Robertsonian translocation?

Answer 23

45–because two long arms are connected and the short arm was lost

Question 24

What are the 3 autosomal trisomies that are relatively viable?

Answer 24

Trisomy 13, 18, 21

Question 25

What are clinical features of Trisomy 13?

Answer 25

close-set or fused eyes, holoprosencephaly, cleft lip/palate, poly- and syndactyly, congenital heart defects, severe mental retardation, short life expecntancy

Question 26

What are clinical features of Trisomy 18?

Answer 26

severe mental retardation, clenched fist, rocker bottom feet, life expectancy <1yr

Question 27

What are clinical features of Trisomy 21?

Answer 27

flattened facial features, congenital birth defects, mental retardation, prominent epicanthal folds, Simean crease, duodenal atreasia

Question 28

What is the overall effect of nondisjunction in mitotic cell divisions in early development?

Answer 28

mosaicism

Question 29

Advancing maternal age is associated with increased risk of ___, particularly in ___?

Answer 29

nondisjunction; meiosis I

Question 30

What are the chromosome numbers of a euploid, haploid, and diploid?

Answer 30

normal; n=23; n=46

Question 31

What is aneuploidy?

Answer 31

abnormal number of chromosomes, such as trisomy or monosomy

Question 32

Triploidy is most commonly caused by ___ whereas tetraploidy is most commonly caused by ___.

Answer 32

dispermy (fertilization by 2 sperm); failure of cell division

Question 33

Describe the most common causes of Trisomy 13, 18, and 21

Answer 33

13-maternal nondisjunction
18-maternal nondisjunction
21-maternal nondisjunction

Question 34

What is Turner syndrome?

Answer 34

Single X: female

ovarian dysgenesis, primary amenorrhea, congenital heart defect, neck webbing, normal intelligence

Question 35

What is the etiology of Turner syndrome?

Answer 35

mostly paternal nondisjunction

Question 36

What is Klinefelter syndrome?

Answer 36

XXY: male

primary hypogonadism, tall and long extremities, gynecomastia, reduced IQ; diagnosis often delayed till puberty

Question 37

Triple X Syndrome

Answer 37

XXX: female

maternal nondisjunction; essentially normal phenotype, mild learning problems, majority are undiagnosed

Question 38

Etiology of 47,XXY Syndrome

Answer 38

maternal meiosis II nondisjunction; essentially normal phenotype, tall, educational and behavioral problems