week 3 Flashcards
what is conventional cytogenetics
Metaphase chromosome analysis
G-banding
what is molecular cytogenetics?
cytogenic analysis at the molecular resolution at all stages of the cycle –> DNa or in situ
at what stage of the cell cycle is the chromsome most visible?
at the metaphase stage during mitosis –> this is around 15 minutes long
what is the G1 stage of cell cycle?
cellular content excluding the chromosome is doubled and this take 6-12 hours
what is the S stage of cell cycle?
each of the 46 chromosomes are duplicated –> 6 too 8 hours
what is the G2 stage of cell cycle?
the cell double checks the chromosome for any erros and makes repairs . 3 to 4 hours
how many bands are there on a chromsome?
550 –> there are bands within bands –> 30000 genes
each band has about 50 genes
explain the chromosome structure
centromere in the middle. Telemore at the ends. P is the short arm and Q is the long arm
types of cytogenic abnormalities?
numerical and structural
what signs can there be that someone has a cytogenic abnormalty?
organ malformation, falcial dysmorphism. Comprised mental and intellectual functioning –> however this has a longer onset time
what does diploidy mean?
two sets of chromosomes
what is aneuploidy?
the gain or loss of a chromosome
what is polyploidy?
this is the gain or loss of a whole set of chromosome
what increases the risk of errors at gametogenesis?
increase in age of paternal and materal, anueploidy
what is meiotic errors ( non disjunction)?
failure of chromosome or chromatid to seperate
what are the clinical features of trisomy 21?
Head
Eyes: upward slanting; brushfield spots
Nose: Small
Ears: abnormally shaped/low set
Tongue: protruding –> because mouth is small
General – flat face, brachycephalic, short neck
Neurological –> Learning disabilities (mild to moderate IQ 30-60)
Hands and feet
single palmar crease
short broad hands
5th finger clinodactyly
wide gap (sandal gap) between the 1st & 2nd toes
what are the statistics for trisomy 21?
1/700 birthds
75% spontaneously abort
what are the affects of trisomy 21 in adults?
fertility not affected for females but is for males.
life expectancy –> 55-658yrs old
medical problems
increase chance of certain cancers ( mainly leukaemia)
hypothyroidsm
alzheimers
obesity,ceoliac, arthritis, diabetes, hearing loss, seizures
what is trisomy 18
edwards syndrome
1 in 6000
95% spontaneous abort
only 10% live over the age of 1
what are the clinical implications for the head for someone with trisomy 18
microcephaly, low set of ears, clift lip and palate, micrognathia
what are the clinical features of the hands and feet for trisomy 18?
clenched hands –> very common, rockbottom feet and overalapping fingers
what are the organ malformation for child with trisomy 18
congential heart disease (90%) umbilical or inguinal hernia congential kidney abnormalities mental retardation short sternum low birth weight eye problems --> cataract and micrognathia
what is trisomy 13?
Patue syndrome, 1 in 12000 live births and 95% spontaenous abortion
what are the symptoms of patue syndrome?
mental retardation, small at birth, microcephaly and sloppping forehead, and also defects of the brain –> holoprosencephaly
what are the phenotype features of trisomy 13?
Eyes – microphthalmia, coloboma, retinal dysplasia, palpebral fissures slanted polydactyly/ flexed fingers abnormal genitalia heart defect cleft lip and palate ears abnormal and low
when does female and male miosis begin?
females miosis begins as early as 5 months of development and finishes at puberty. However in males does not start till puberty
what are the two steps that can causes autosomal aneuploidy for the prenatal fetus?
unfavourable chiasmata distribution (foetus)
and also age dependent deterioation of the fetus –> as the female gets older the more affect the enviroment such as radation, alcohol, drugs has on there uterus
is the phenotype less affected in sex chromosome mutation or autosomal ones?
sex chromosomes
what is the chromosome strcuture for klinefelter and Turners syndrome?
Turners is 45 (x) –> 1 in 2500
Klinefelter is 47 (XXY) 1 in 1000
what are the features of turners syndrome?
reproductive –> loss of ovarian function, won’t go through puberty unless given some hormone treatment and infertility
lymphatics –> webbed neck–> swelling of hands or/& feet
other–> coarctation of aorta, short stature as she does not go through puberty –> IQ normally reduced compared to SIBs
what is the diagnosis of klinefelter syndrome?
64% is not diagnosed –> usually diagnosed when they try have kids –> infertile or if they develop hypogonadism
what affect will klinefelter syndrome have on infertility
May lack secondary sexual characteristics
Testicular dysgenesis
Reduction in sperm count
30-50% gynaecomastia (20x risk breast cancer)
what is the growth and IQ of patients with kilinefelter syndrome ?
will be normal when a child but accelerate very quickly –> long arms and legs
IQ –> depends a lot on there family and also how many x’s they have
what are the three causes of triploidy?
dispermy, digny, diplospermy
what happens with double paternal in chromosomes numbers
promote large placeneta and some growth delay
what happens with double maternal in chromsomes numbers?
tiny placenta, significant delay in growth and head-saving macrocephaly due to the small placenta
what does the paternal and maternal sex chromosome code for?
maternal –> foetus and paternal –> placenta
what is mosaicism ?
it is miototic non disjunction
what is reciprocal translocation?
when two parts of different chromosomes swap –> 1 in 500 chance. 5-10% phenotype risk
reproductive risk
what the acrocentric chromosomes?
13,14,15,21 and 22 –> shorter chromosomes
what is robertsonian translocation?
it is when 2 acrocentric chromosomes come together and the long q arms join together and discard of the short arms
what is unbalance rearrangment?
the gain or loss of huge amount of chromosomes/DNA –> can cope with gain a lot better than loss. It is usually sporadic and can be due to deletion or duplication
what is . Interstitial deletion?
when a section of a chromosome is lost
what is terminal deletion?
when a chuck of chrosome is lost from teh terminal ends
what is duplication of a chromosome?
when a section of the chromosome is duplicated
what is a ring chromosome?
when bits of either end of the chromosome breaks and forms a ring
