Chromosomal Abnormalities Flashcards
What is chromatin made of?
DNA, non-histone proteins, RNA, histones (H2A, H2B, H3 & H4 octamer - H1 stabilises octamer)
What are the different types of numerical chromosomal abnormalities?
Polyploidy, aneuploidy, monosomy and trisomy
What are the different types of structural chromosomal abnormalities?
Physical changes to one or more of the chromosomes - balanced or unbalanced.
In a karyotype how are the chromosomes aligned?
Largest to smallest from (1-22) with 23 at the end
How do you write out a karyotype formula?
Starts with total number of chromosomes on the cell, followed by a comma, then the X chromosomes and Y chromosomes. + or - indicates an extra/missing piece e.g. 6p- means missing a segment of the p-arm on chromosome 6
Why would you perform a karyotype?
Congenital abnormalities (prenatal screening, birth defects, abnormal sexual development, infertility, recurrent foetal loss), acquired abnormalities
How would prepare cells for a karyotype?
Procure cells, add phytohaemagglutin, culture, add colcemid, culture, brief digestion with trypsin, Giemsa stain.
What is the culturing time length for bone marrow?
0-1 day
What is the culturing time length for blood?
2-3 days
What is the culturing time length for solid tissue, amniotic fluid and chorion villus?
7-21 days
When is chromatin activated?
When it’s acetylated
When is chromatin inactive?
When it’s methylated
What is non-disjunction?
Creation of a gamete with a missing chromosome or containing both homologous chromosomes i.e. failure of chromosome pairs to separate properly
What causes aneuploidy?
Non-disjunction
How can non-disjunction arise?
Failure of homologous chromosomes to separate in meiosis I or failure of sister chromatids to separate during meiosis II
What are the possible autosomal trisomies in humans?
21, 18 & 13
What is anaphase lag?
Chromosome which are left behind at cell division (due to defects in the spindle fibres)
What are the three types of chromosomal structures in humans?
Meta-centric, sub-metacentric and acrocentric
What are the types of mutations that occur in one chromosome?
Deletion, duplication, inversion, ring chromosome and isochromosome
What are the types of mutations with two chromosomes?
Inversion, reciprocal translocation, robertsonian translocation
Where is polyploidy common?
Human muscle and liver
What is sex chromosome aneuploidy?
Only one X is active in human cells. Inactive forms - Barr bodies in periphery of cells
What are the symptoms of Down syndrome?
Intellectual disability, congenital heart disease, haematological malignancies, hypothyroidism, infertility, eye disorders, hearing disorders
What is the karyotype for Edwards syndrome?
(47,XX,+18) - modal life span of ~5-15 days
