19

Question 1

What are the differences between nuclear and mitochondrial genome

Answer 1

Mitochondrial genome: maternally inherited
13 protein coding genes
16.6 x 10^3 base pairs
1 circular DNA molecule

Nuclear genome:
from both parents
20,000 protein coding genes
3.2 x 10^9 base pairs
46 chromosomes

Question 2

in karyotypes, what stage are the chromosomes in

Answer 2

metaphase

Question 3

what’s a centromere

Answer 3

structure linking the short arm (p) and the long arm (q) together.

Attaches sister chromatids to microtubule

Question 4

what is g banding

Answer 4

staining technique used to generate a karyotype.

g light bands are:
gene rich
GC rich
early replicating

G dark bands are
gene poor
AT rich
Late replicating

Question 5

what’s aneuploidy

Answer 5

abnormal number of chromosomes

Question 6

what’s disomy

Answer 6

two copies of a chromosome (normal)

Question 7

what percentage of the genome is coding sequence

Answer 7

1.6%

Question 8

example of control elements

Answer 8

enhancers, repressors, promoters

Question 9

what’s a pseudogene

Answer 9

non-functional copy of a gene; arises from gene duplication followed by deleterious mutation in one copy

Question 10

What are repetitive sequences

Answer 10

tandem repeats of closely related DNA sequences; constitute about 40% of human genome

Question 11

what’s polyploidy

Answer 11

gain of one or more haploid chromosome

Question 12

what’s chromosome translocation

Answer 12

Joining of part of one chromosome to a second chromosome. In a reciprocal/balanced translocation, part of the second chromosome joins to the first chromosome so that there is no net loss or gain of material

Question 13

what’s ROBERTSONIAN TRANSLOCATION

Answer 13

Two chromosomes joining at their centromeres. the smallest one is usually lost.

Question 14

most common sex chromosome abnormalities

Answer 14

turner syndrom

klinefelter syndrone

Question 15

most common autosome abnormalities

Answer 15

downe syndrome
edwards syndrome
patau syndrome

Question 16

most common all chromosome abnormalities

Answer 16

triploid –> non viable

Question 17

how many chromosomes in triploidy

Answer 17

69

Question 18

what are some key clinical features of down syndrome

Answer 18

Distinct facial appearance

Marked muscle hypotonia as baby 

May have single palmar crease 

Learning difficulty (IQ usually <50) 

Congenital heart malformations (40%) 

1 in 700 live births

> 60% are spontaneously aborted
20% are stillborn

Question 19

what’s a risk factor for trisomies

Answer 19

increase in maternal age

Question 20

what three patterns of chromosomes can cause down syndrome

Answer 20

trisomy 21 (95%)

robertsonian translocation

mosaicism

Question 21

Edwards syndrome characteristics (TRISOMY 18)

Answer 21

1 in 3000 births
multiple malformations (especially heart, kidneys)
clenched hands with overlapping fingers

POOR PROGNOSIS

Question 22

Patau syndrome characteristics (TRISOMY 13)

Answer 22

1 in 5000 births
multiple malformations
affects midline structures particularly:
incomplete lobation of brain; cleft lip; congenital heart disease

POOR PROGNOSIS

Question 23

Klinefelter syndrome characteristics

Answer 23

47,XXY
1 in 1000 males
Infertility (atrophic testes do not produce sperm)
Poorly developed 2ndary sexual characteristics in some (lack of testosterone)
Tall

Question 24

Turner syndrome characteristics

Answer 24

45,X
1 in 5000 females
99% are lost spontaneously in pregnancy
Short stature
Primary amenorrhoea (ovaries involute before birth)
Congenital heart disease (coarctation of aorta) 20%

Question 25

what are the prenatal genetic screens available and when are they done

Answer 25

amniocentesis 15-18 weeks post implantation

chorionic villus sampling 12-14 weeks post implantation

non invasive prenatal testing 11-14 weeks post implantation (ultrasound imagineer of nuchal translucency which is fluid at the back of the neck or cell-free DNA in mothers plasma)

Pre implantation screening for IVF

Question 26

explain the process of x inactivation=Lyonization

Answer 26

X chromosome contains approximately 1100 genes.
early in embryonic development, one of the x chromosomes is shut off (not the same in all cells)

pseudoautosomal region of X chromosome do not undergo inactivation.

Question 27

which region of the X chromosomes does not undergo inactivation and why

Answer 27

psuedoautosomal region because it contains genes which are also present in y chromosome

Question 28

what gene is responsible for x inactivation

Answer 28

Xist gene which is encoded in the X-Inactivation Centre (XIC)

Question 29

what are Barr bodies

Answer 29

structures on the edge of the nucleus of cells with transcriptional inactivation. they are inactive x chromosome

Question 30

what’s a somatic cell

Answer 30

any cell of a living organism other than the reproductive cells.

Question 31

what’s a germ cell

Answer 31

a cell containing half the number of chromosomes of a somatic cell and able to unite with one from the opposite sex to form a new individual;

Question 32

in what cells is x inactivation reversed

Answer 32

germ cells

Question 33

what important gene does the Y chromosome encode

Answer 33

“Sex Determining Region of the Y-chromosome” – the SRY gene

Question 34

what does the SRY gene encode

Answer 34

a protein that is a member of the HMG group of transcription factors

Question 35

what gene is responsible for make sex determination

Answer 35

SRY gene