Chromosomal Disorders ✅ Flashcards
Where are chromosomes found?
In the nucleus of every nucleated cell
What does each chromosome consist of?
DNA that is tightly coiled around proteins known as histones that support its structure
What does much of what we know about chromosomes come from?
Observations during cell division
Why does much of what we know about chromosomes come from observations during cell division?
Because the DNA becomes more tightly coiled, and is thus visible under a microscope
How many chromosomes do humans normally have?
46
What are the 46 chromosomes made up of?
22 pairs of numbered chromosomes (autosomes) and one pair of sex chromosomes (XX or XY)
What is a centromere?
A constricted region of each chromosome
What are the regions on either side of the centromere known as?
The chromosomes ‘arms’
What is the shorter arm of the chromosome known as?
The p arm
What is the longer arm of the chromosome known as?
The q arm
What are the ends of the chromosomes known as?
Telomeres
What is each chromosome arm divided into?
Regions, or bands
How can the bands of chromosomes be seen?
Microscopically with special stains
How are the bands of chromosomes labelled?
By counting out from the centromere, with p1 and q1 being the closest to the centromere
What is found within the bands of the chromosomes?
Sub-bands
How are sub-bands numbered?
Outwards from the centromere
What can chromosomal abnormalities be classified into?
- Numerical abnormalities
- Structural abnormalities
What do numerical chromosome abnormalities involve?
Missing or extra whole chromosome from a pair
What is it called when a whole chromosome is missing?
Monosomy
What is it called when there are extra chromosome?
Trisomy or tetrasomy
Give 2 examples of disorders cause by numerical abnormalities of chromosomes
- Turner’s syndrome
- Down’s syndrome
What is the chromosomal abnormality in Turner’s syndrome?
Monosomy X
What is the chromosomal abnormality in Down’s syndrome?
Trisomy 21
What forms can structural abnormalities of chromosomes take?
- Translocation
- Insertion
- Deletion
- Inversion
- Duplication
- Ring
What is a translocation?
A portion of one chromosome is transferred to another chromosome
What is an insertion?
A segment of a chromosome is inserted into another position on a chromosome
What is a deletion?
A portion of the chromosome is missing
What is an inversion?
A portion of chromosome has broken off, turned upside down, and reattached
What is a duplication?
A portion of the chromosome is duplicated, meaning there is extra genetic material
What is a ring chromosomal abnormality?
A chromosome has formed a circle
Does a ring chromosomal abnormality have a loss of genetic material?
Can occur with or without
