chromosomal disorders

Question 1

human karyotype

Answer 1

chromosome analysis test evaluates the number and structure of a person’s chromosomes in order to detect abnormalities (gross screen of human genetic material)

• performed on any dividing cell
• screen test

Question 2

define aneuploidy and how it is caused

Answer 2

chromosome number that is not a multiple of the normal haploid number (=23)
caused by non-disjunction during meiosis

Question 3

trisomy

Answer 3

gain of 1 chromosome

Question 4

monosomy

Answer 4

loss of 1 chromosome

Question 5

down syndrome

Answer 5

• congenital condition
• chromosome 21 trisomy
• diagnostic test human karyotype
• increased incidence with increased paternal age

Question 6

congenital vs acquired conditions

Answer 6

congenital are conditions existing at or before birth (germline)

Question 7

mosaicism

Answer 7

somatic chromosomal abnormality occurring post-zygote formation, from non-disjunction

Question 8

structural chromosome abnormalities

Answer 8

• reciporocal translocation
• robertsonian translocation
• inversion
• deletion
  (can be noth constitutional and acquired)

Question 9

reciprocal translocation

Answer 9

is a two-way exchange of material between two non-homologous chromosomes

constitutionally = normal phenotype due to no loss or gain of chromosome material

acquired = can result in an abnormal phenotype, as it brings together two genes normally far apart

Question 10

how do carriers of reciprocal translocations present

Answer 10

• recurrent miscarriages
• chromosome examination of products of conception
• and more

Question 11

inversion

Answer 11

a flip of chromosome material = structural rearrangement
involves two breaks on the same chromosome
- carriers usually phenotypically normal

Question 12

deletion

Answer 12

loss of chromosomal material

- always results in a genetically unbalanced chromosome complement

Question 13

terminal deletion

Answer 13

caused by a single break at the terminal region of chromosome and loss of that fragment

Question 14

interstitial deletion

Answer 14

caused by two breaks in the same chromosome and loss of the intervening fragment

Question 15

chromosomal tests

Answer 15

• karyotype analysis

- FISH (fluorescent in situ hybridization)

Question 16

what are chromosomal tests used for

Answer 16

tests used to look at abnormalities in the number of chromosomes or big translocations and deletions of chromosomal material

Question 17

when would karyotype analysis be carried out

Answer 17

suspected congenital disorders e.g. down syndrome or recurrent miscarriages

cancer / leukemia
- information helps with diagnosis and prognosis and even influence treatment given

Question 18

differences between karyotype analysis and FISH

Answer 18

karyotype analysis requires dividing cells, whole genome scan

FISH = an adjacent to chromosome analysis looks at specific genes/parts of genes only

• don’t need dividing cells just any with a nucleus
• both congenital and acquired