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what is conventional cytogenetics

Metaphase chromosome analysis


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?

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)
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