Numerical And Structural Abnormalities

Question 1

What is euploidy?

Answer 1

Exact multiples of haploid chromosome set. Humans are diploid; any more is not compatible with life (triploidy or tetraploidy)

Question 2

How do you get tetraploidy?

Answer 2

Post meiotic event; presents as a duplication of a diploid complement most likely due to a failed early mitotic cleavage

Question 3

How does triploidy occur?

Answer 3

can be due to failure of gametogenesis of one of the mitotic divisions giving a 2N gamete that gets fertilized by another gamete
-or a 3N complement can come from dispermy

Question 4

aneuploidy

Answer 4

gain or loss of individual chromosomes; trisomy or monosomy

Question 5

What is the only viable monosomy?

Answer 5

Turner’s syndrome

Question 6

What are the 3 live-born trisomys?

Answer 6

Chromosome 21: Down’s
Chromosome 13
Chromosome 18

Question 7

Aneuploidies are usually a result of____

Answer 7

meiotic or mitotic nondysjunction

Question 8

Are aneuplodies inherited?

Answer 8

Not usually

Question 9

What are the 3 basic components of chromosomal nomenclature?

Answer 9

• total number of chromosomes
• sex chromosome complement
• any chromosomal abnormalities

Question 10

If a meiotic error produces a gamete with 2 copies of chromosome A what will happen?

Answer 10

fertilization with a normal gamete will result in trisomy

Question 11

Is it possible for a embryo with trisomy 21 to produce disomic cell?

Answer 11

Yes; it would be mosaic

Question 12

What is mosaicism?

Answer 12

presence of at least 2 different cell lines with at least one clear variation between them

Question 13

How is a mosaic different from a chimera?

Answer 13

mosaic individuals have fewer variations

chimeras have many variations traced back to their cell lines

Question 14

Trisomy 21 characteristics include

Answer 14

short stature
low set ears
microcephaly
mental retardation 
upslanting eyes
short hands
eye folds 
protruding tongue
infertile

Question 15

Trisomy 13 (Patau syndrome) characteristics

Answer 15

-failure to thrive
-cleft lip and palate
-rocker bottom feet
polydactyly
-punched out scalp
-small head
-heart defect

Question 16

Symptoms of Trisomy 18 (Edwards syndrome)

Answer 16

• low birthweight
• small mouth/jaw
• ventricular septal defect
• hypoplasia of muscles
• prominent occiput
• low set malformed ears
• rocker bottom feet
• crossed fingers
• -outlook is bleak even if the infant survives the 1st year

Question 17

Sex chromosome aneuploidies are frequently more mild than autosomal aneuploidies because

Answer 17

of X inactivation

Question 18

Describe XXX female.

Answer 18

1/1000 births, usually due to maternal meiosis I error

• average to tall stature
• learning deficit possible
• some fertility problems possible`

Question 19

Describe XYY

Answer 19

-1/1000 male live births
-failure of paternal meiosis
-tall stature
-normal intelligence
normal fertility
-indistinguishable from xy
-originally it was thought that these people has an increased testerone and thus increased propeensity for violence, but not true

Question 20

Klinefelter syndrome

Answer 20

• 1/1000 male life births
• 50% due to meiosis I error in father
• tall stature
• infertility
• some female characteristics may develop
• learnign deficiency possible

Question 21

Turner Syndrome

Answer 21

• incidence: 1/5000 live female births
• short stature
• webbed neck
• edema of the hands and feet at birth; after birth, short hands and feet
• heart and renal anomalies
• increased carrying angle of the elbow
• shield chest
• low posterior hairlline
• normal intelligence, some learning disability
• usually infertile

Question 22

How does Turner Syndrome arise?

Answer 22

about half have 45, X karyotype

• 15% have deletion or rearrangement on X
• 10% more are mosaics 45X/46, XX; or 45X, 46 XY

Question 23

Males that have the mosaic male female Turner syndrome pattern are usually ok. Why aren’t the girls?

Answer 23

They are at increased with of gonadoblastoma–> gonad removal recommended

Question 24

What are the major issues of Turner syndrome?

Answer 24

growth hormone to prevent short stature

• monitor for heart malfuncitons
• karyotype to be sure no Y chromosome is present
• counseling for probable infertility

Question 25

Why is it important to diagnose Turner syndrome?

Answer 25

• some treatments are available and they need to be administered early to be most effectve
• if gonadoblastoma is an issue, surgical removal needs to be planned
• parent needs to be aware of what the child is at risk for

Question 26

What is androgen insensitivity?

Answer 26

testicular feminization where the Y chromosome is intact and the TDF present and functional

• androgen receptor has a mutation and no androgen receptor protein is produced
• further male differentiation cannot occur
• female default development takes place, but infertile