19 Flashcards
What are the differences between nuclear and mitochondrial genome
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
in karyotypes, what stage are the chromosomes in
metaphase
what’s a centromere
structure linking the short arm (p) and the long arm (q) together.
Attaches sister chromatids to microtubule
what is g banding
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
what’s aneuploidy
abnormal number of chromosomes
what’s disomy
two copies of a chromosome (normal)
what percentage of the genome is coding sequence
1.6%
example of control elements
enhancers, repressors, promoters
what’s a pseudogene
non-functional copy of a gene; arises from gene duplication followed by deleterious mutation in one copy
What are repetitive sequences
tandem repeats of closely related DNA sequences; constitute about 40% of human genome
what’s polyploidy
gain of one or more haploid chromosome
what’s chromosome translocation
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
what’s ROBERTSONIAN TRANSLOCATION
Two chromosomes joining at their centromeres. the smallest one is usually lost.
most common sex chromosome abnormalities
turner syndrom
klinefelter syndrone
most common autosome abnormalities
downe syndrome
edwards syndrome
patau syndrome
most common all chromosome abnormalities
triploid –> non viable
how many chromosomes in triploidy
69
what are some key clinical features of down syndrome
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
what’s a risk factor for trisomies
increase in maternal age
what three patterns of chromosomes can cause down syndrome
trisomy 21 (95%)
robertsonian translocation
mosaicism
Edwards syndrome characteristics (TRISOMY 18)
1 in 3000 births
multiple malformations (especially heart, kidneys)
clenched hands with overlapping fingers
POOR PROGNOSIS
Patau syndrome characteristics (TRISOMY 13)
1 in 5000 births
multiple malformations
affects midline structures particularly:
incomplete lobation of brain; cleft lip; congenital heart disease
POOR PROGNOSIS
Klinefelter syndrome characteristics
47,XXY
1 in 1000 males
Infertility (atrophic testes do not produce sperm)
Poorly developed 2ndary sexual characteristics in some (lack of testosterone)
Tall
Turner syndrome characteristics
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%
what are the prenatal genetic screens available and when are they done
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
explain the process of x inactivation=Lyonization
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.
which region of the X chromosomes does not undergo inactivation and why
psuedoautosomal region because it contains genes which are also present in y chromosome
what gene is responsible for x inactivation
Xist gene which is encoded in the X-Inactivation Centre (XIC)
what are Barr bodies
structures on the edge of the nucleus of cells with transcriptional inactivation. they are inactive x chromosome
what’s a somatic cell
any cell of a living organism other than the reproductive cells.
what’s a germ cell
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;
in what cells is x inactivation reversed
germ cells
what important gene does the Y chromosome encode
“Sex Determining Region of the Y-chromosome” – the SRY gene
what does the SRY gene encode
a protein that is a member of the HMG group of transcription factors
what gene is responsible for make sex determination
SRY gene
