TBL 6

Question 1

down syndrome

Answer 1

• Trisomy 21 accounts for 95% of Down Syndrome cases

risk increase with maternal age

Ovum is the source of 95% of trisomy cases,

nonisjunction during gamete formation

karyotype: 47,XX,+21

Question 2

Clinical Features of Down Syndrome

Answer 2

12 to 14 characteristics that can
develop in Down Syndrome → affected individuals
express 6 to 8 characteristics on average.

flat facial profile, oblique
palpebral fissures, epicanthic folds, palmar crease,
clinodactyly.

Approximately 40% of the patients have congenital heart
disease.
* Children with Down Syndrome also have a high risk of
developing leukemia.
* Virtually all patients with trisomy 21 older than age 40
develop neuropathologic changes characteristic of
Alzheimer disease.

Question 3

mosaic down syndrome

Answer 3

1%

mitotic nondisjunction of chromosome 21 during embryogenesis.

symptoms are milder

Question 4

Trisomy 18 - Edwards Syndrome

Answer 4

• Trisomy 18 is the second most common autosomal trisomy after 21 → incidence
  is 1:8,000.
• In individuals with Edwards Syndrome, death usually occurs by age 1.
• Clinical presentation includes hypertonia, prenatal growth deficiency,
  characteristic fist clench, rocker-bottom feet, receding jaw, and low set ears.

Question 5

Trisomy 13 - Patau Syndrome

Answer 5

• Clinical features include
  microcephaly, sloping forehead,
  characteristic fist clench, rocker-
  bottom feet, polydactyly, cleft lip
  and palate.
• 50% of children die within the
  first month, 90% within the first
  year.

Question 6

Klinefelter Syndrome can result from

Answer 6

nondisjunction that can take place both in meiosis I
and meiosis II of maternal oogenesis or during meiosis I of paternal
spermatogenesis

Question 7

clinical presentation of Klinefelter Syndrome

Answer 7

Classically, KS patients are of male appearance with very small, firm
testes, gynecomastia and tall stature with long legs and a relatively short
trunk.
* Infertility is almost always observed in KS men, frequently leading to its
diagnosis.
Klinefelter Syndrome

Question 8

Klinefelter syndrome (KS) is the most frequent sex chromosome disorder
of the male population, accounting for almost _________
males and the most frequent form of male hypogonadism.

Answer 8

1 in every 650 newborn

• 90% of cases result from 47,XXY

Question 9

Male hypogonadism –

Answer 9

Male hypogonadism – two or more X chromosomes + one or more Y
chromosomes

Question 10

example of monosomy

Answer 10

turner syndome

Question 11

Turner Syndrome (TS) is one of the most common sex
chromosome abnormalities, affecting approximately ______
live-born girls

Answer 11

1 in 2000

• Hypogonadism in phenotypic females

Question 12

prognosis of turner

Answer 12

Most cases of Turner syndrome are non-viable and end in
spontaneous abortion, though if the baby is born, the prognosis
is excellent.

Question 13

• Complete or partial monosomy of the X chromosome:_____ % are___

Answer 13

~57% are 45,X

Question 14

balanced vs unbalnced chromosomes

Answer 14

Structural rearrangements are classified as
balanced, if the genome has the normal
complement of chromosomal material, or
unbalanced, if there is additional or missing
material.

Question 15

robersonian traslocation

Answer 15

About 4% of Down syndrome cases result from a
translocation of the long arm of chromosome 21 onto
another chromosomes (22 or 14) → Robertsonian
Translocation
* Unlike standard trisomy 21, shows no relation to
maternal age

high risk to passing on if carrier, especially in female carrier

Question 16

Oncogenic Chromosome Translocations

what is the chromosome called

what does it cause

Answer 16

9 chrom gene goes on chrom 22

The most well studied is the Philadelphia chromosome (Ph1)
which is a result of a translocation between chromosome 9
and 22 → causing chronic myelogenous leukemia (CML)

proto-oncogene abl1 (tyrosine
kinase that activates signal pathways)
moves to chrom 22q to chrom 9 q and get inserted infront of bcr

abl1-bcr always turned on so can lead to continued cell proliferation, inhibition of cell differentiation,
and cell death.

Question 17

examples of translocations

Answer 17

robertsonian down syndrome and ocogenic translocation

Question 18

what does oncogenic chromosome translocation cause

Answer 18

chronic myelogenous mutation

Question 19

examples of chromosome deletions

Answer 19

digeorge syndrome and cri-du-chat

Question 20

digeorge syndome’s deletion

Answer 20

deletion within 22q11.2 (distal) on chromosome 22

due to unequal crossing over

Question 21

cri-du-chat deletion

Answer 21

deletion of small terminal portion of chromosome 5 p arm

Question 22

clinical presentation of cri-duchat

Answer 22

microcephaly, epicanthal folds, low-set ears, micrognathia (low set, small jaw ), cat-like cry, intellectual disability

due to haploinsuffiency (not enough gene to have enough product)

Question 23

Amniocentesis or chrionic villus sampling (CVS) :

Answer 23

Fetal cells obtained from
amniotic fluid or chorion of placenta

Question 24

Nuchal translucency (NT) scan -

Answer 24

measures the clear (translucent) space in the tissue at the back of your baby’s neck (11 – 14 week ultrasound)

Question 24

• NIPGD: Noninvasive prenatal genetic diagnosis -

Answer 24

Fetal cells and DNA obtained
from maternal circulation

Question 25

primary oocytes are surrounded by granulosa cells and called _____

Answer 25

primordial follicle

then that become primary follicle then secondary follicle then enlarges to mature (graafian) follicle

Question 25

what happens when the oocyte exits from dictyate arrest

Answer 25

LH cause resume in meiosis 1. nucleus breaks down and chrom line up at metaphase 1. Homologs go to opposite poles. one set of homolgs in oocyte and the other in polar body

Question 26

what happens during meosis 11 in oocyte

Answer 26

mature egg is arrested in meta II and trasported to oviduct during ovulation

only comples meiosos II when fertilized

Question 27

types of chromosome rearrangement

Answer 27

aneuploidy, deletions, duplications, rearrangements (translocation)n

Question 28

whats a normal karyotype

Answer 28

46, XX. 46, XY