Chromosomal Abnormalities Flashcards
What is a karyotype?
Picture of the systematic assortment of the complete set of chromosomes of an individual
Chromosomes grouped by size and centromere location
note: humans have no telocentric chromosomes
How are chromosomes stained?
1) Obtain a dividing source of cells e.g. blood, amniotic fluid
2) Halt at metaphase
3) Giesma stain (stains phosphate groups of A-T pairs)
4) Light microscopy (show G-banding)
What is polyploidy? What can cause it?
Multiple of haploid chromosome no. greater than the diploid no.
e.g. 3n (triploidy)
Polyspermy = fertilisation of egg by more than one sperm
What is aneuploidy? What can it be caused by?
Abnormal no. of chromosomes which is not a multiple of the haploid no.
- MONOSOMY = loss of one homologous chromosome
- TRISOMY = gain of one homologous chromosome
Caused by non-disjunction
What is non-disjunction?
Failure of sister chromatids (mitosis) or homologous chromosomes (meiosis) to separate, leading to daughter cells with an abnormal no. of chromosomes
What is the difference between mosaicism and chimerism?
Mosaicism = two populations of cells with different karyotypes in one individual that have emerged from one zygote
Chimerism = two populations of cells with different karyotypes in one individual that have emerged from more than one zygote
What is anaphase lag?
Delayed movement in anaphase due to defects in spindle function or attachment to chromosomes, which often leads to the entire loss of a chromosome.
What are three examples of trisomies?
Down’s (trisomy 21)
Edward’s (trisomy 18)
Patau’s (trisomy 13)
Describe some of the signs and symptoms of Down’s syndrome.
Mild/moderate intellectual disability Congenital heart disease Constipation (GI lacks nerves) Infertility (males)/ reduced fertility (females) Simian crease in hands Epicanthial fold etc.
What are some examples of sex chromosome aneuploidies?
Females:
Turner’s syndrome (X)
Triple X syndrome (XXX)
Males:
Klinefelter’s syndrome (XXY)
XYY syndrome
What are Barr bodies?
Condensed X chromosomes found at cell periphery - inactivated (lyonisation)
Only one X chromosome active in any human cell
Describe the signs and symptoms of Turner’s syndrome.
Female (XO)
Short stature Broad chest Low-set ears Webbed neck Infertility & amenorrhoea No mental retardation etc.
Why does Turner’s syndrome cause problems although males only have one X chromosome?
Both the X and Y chromosomes have pseudo-autosomal regions as well as sex-related genes
Describe the signs and symptoms of Triple X syndrome.
Female (XXX)
Tall stature Microcephaly (small head) Delayed motor skills + speech and learning disabilities Scoliosis Auditory processing defects etc.
Describe the signs and symptoms of Klinefelter’s syndrome. What is the treatment?
Male (XXY)
Reduced testosterone
Gynaecomastia (note: increased breast tissue, not increased adipose tissue)
Language learning and reading impairment
etc.
Treatment: hormone replacement & surgery
