chromosomal abnormalities

cytogenetics

study of structure and function of chromosomes

use of cytogenetics

for screening and diagnosing inherited chromosomal disorders

karyotyping

preparation of chromosomes arranged in size order

karyotype preparation

growth medium added to blood, phytohaemagglutinin added (stimulates mitosis), incubated, treated with colcemid (stops mitosis in metaphase), cell centrifuged and lysed, fixed and stained with giemsa

how can chromosomes be identified

length, banding pattern, centromere placement

metacentric

centromere in centre

sub-metacentric

off centre centromere

acrocentric

centromere very close to end

polyploidy

extra whole sets of chromosomes

aneuploidy

additional or missing chromosomes

monosomy

2n - 1

trisomy

2n + 1

non-disjunction

cause of aneuploidy - chromosomes don't separate properly so the wrong numbers end up in the daughter cells

downs syndrome - chromosomal name

47 xx/y +21

downs syndrome characteristics

characteristic facial features, short stature, some level of learning disability, heart defects

turners syndrome

only viable monosomy - 45 XO

turners syndrome characteristics

phenotypically female, sterile due to lack of maturation of sex organs - oestrogen replacement therapy used for development of secondary sex characteristics

klinefelters syndrome

47 XXY - one of the most common genetic abnormalities

klinefelters characteristics

essentially male but with some female characteristics

tall, sterile, treated with testosterone HRT

types of chromosome mutations

deletion, duplication, inversion, reciprocal translocation

g band structure

each has a short arm (p) and long arm (q), each band is given an address so specific mutations can be described

cri-du-chat cause

deletion of part of chromosome short arm

cri-du-chat characteristics

defects in glottis and larynx, wide face, physical and intellectual disability

prader-willi cause

deletion in long arm of chromosome 15, occurs when affected chromosome is inheritied from the father

Prader-Willi characteristics

uncontrollable eating later in life, obesity, diabetes, poor sexual development in males

angelmann's cause

deletion of long arm of chromosome 15 - only when the segment is missing from the maternally derived chromosome

angelmann's characteristics

happy demeanour, outbursts of laughter, speech problems, seizures, intellectual disability

familial downs syndrome cause

one chromosome 21 is attached to a chromosome 14

chronic myelocytic leukaemia cause

22-9 translocation

chronic myelocytic leukaemia effects

spontaneous - translocation creates BCR-ABL gene which is an oncogene that stimulates overproduction of white blood cells