Cytogenetics (Chromosomal) Flashcards
What phase of mitosis are the Chromosomes most visible?
Metaphase
What are the ends of chromosomes known as?
Telomeres
The short arm of the chromosome is also know by which letter?
P
The long arm of the chromosome is also known by which letter?
q
Approximately how many genes and bands make up a karyotype?
550bands 30kGenes
Is loss or gain of chromosomes worse?
Loss
What is position effect?
Chromosome in new environment will function differently = different phenotype
Is sex chromosome or autosome imbalance worse?
Autosome imbalance is more severe
What does aneuploidy mean?
Gain or loss of chromosomes
What is mosaicism in terms of karyotype/cells?
Some are diploid (normal) and some have aneuploidy!
An increase in maternal age can increase the likelihood of what?
Aneuploidy
An increase in paternal age can increase the likelihood of what?
Nothing (well no aneuploidy)
In meiosis when are the chiasmata visible?
Metaphase I
In meiosis when are the chromosomes separated?
Anaphase I
What happens in meiosis II?
Mitotic division of the secondary gametocyte - Chromatids separate = mature sex cell produced
What is non disjunction?
A meiotic error
When does most non-disjunction occur (%) ?
Meiosis I (80-90%)
In trisomy one you are at greater risk of what?
Leukaemia, hypothyroidism, alzheimers + more
Which of males of females are usually infertile with trisomy 21?
Males
What percentage of trisomy 21 foetus’s spontaneously abort?
75%
What is the risk of trisomy 21 at a normal age?
1/700
Trisomy 18 is called what? risk and spontaneous abortion stats?
Edward’s syndrome, 1/6000 95% spontaneous abortion
Features of Edward’s syndrome
Short lifespan, microcephaly, sort sternum, low birth weight
Most common organ abnormality in trisomy 18?
Congenital heart disease (90%
Trisomy 13 stats?
Patau syndrome, 1/12000 (95% spont abort)
features of trisomy 13?
Small eyes, cleft lip and palate, polydactyly-fingers flexed heart defects - severe retardation
Why is trisomy 13, 18 and 21 more commonly seen than others?
Small chromosomes- others tend to be lethal although these do have high rates of abortion
At what age do female ages start and remain at Meiosis I ?
5 months, suspended until puberty
Karyotype of turner’s syndrome?
45X (affects females)
Fertility issues with turners syndrome?
Infertility, no ovarian function or puberty
Lymphatic issue of Turner’s?
Webbed neck, swollen feet
Turner’s syndrome causes what structural problems?
Coarction of aorta, and short stature
What is a common reason for diagnosis of klinefleters?
Inferitlity or Agenesis of sperm!
Stature of klinefelter’s ?
Tall, long arms and legs!
Klinefelter’s has a high risk of what cancer due to what?
Due to gynaecomastia 20X risk of breast cancer
What is Digyny?
A diploid egg
Double maternal contribution gives what?
Big head!!
Double paternal contribution?
Foeutus many abnormalities, cystic placenta
contribution of dad = what and mum = what?
Mum = head Dad = Placenta
Molar pregnancy is what?
Conception but not embryo!, only a placenta
what is the consequence of mosaicism on phenotype?
Variable. possibly less lethality!
Females are mosaic?
X inactivations
13, 14, 15, 21 and 22 are known as what?
Acrocentric chromosomes
P arms do or do not contain coding DNA?
Do not!
Robertsonian translocation involves what?
Fusions of two Qarms no P arms have 45 chromosomes
Inversion of chromosomes involves what?
Two breaks in chromosomes rotation etc
2 breaks in one arms is knows as what?
Paracentric inversion
2 breaks in different arms is what?
Pericentric! inversion
unbalanced rearrangements are usually inherited?
No sporadic!
Unbalance rearrangement more likely in which sex?
Males
What types of deletion can occur?
Interstitial or terminal
