Chromosomes Flashcards
What is a chromosome?
A thread-like structure made up of DNA
Where are chromosomes found?
Nucleus of each cells
What is the role of chromosomes?
Allow DNA to be accurately copied during cell divison
How many chromosomes are in each cell?
46 individual chromosomes
23 pairs of chromosomes
What determines gender?
Every egg has an X sex chromosome; a sperm can have either an X or a Y sex chromosome.
If the sperm that fertilizes an egg has an X chromosome, the baby is female; if it has a Y chromosome, the baby will be a boy.
What is the main protein present in a chromosome?
Histones - largely positive globular proteins
What is the role of histones?
Organise and condense DNA tightly so that it fits into the nucleus
What is chromatin?
Tightly coiled combination of DNA and proteins
What are telomeres?
DNA-protein structures that form protective caps at the end of chromosomes.
What are telomeres repeats of?
5’-TTAGGG-3’ repeats
What are centromeres?
The region of a chromosome to which the microtubules of the spindle attach, via the kinetochore, during cell division.
What do centromeres help with?
Helping the cell divide up its DNA during division (mitosis and meiosis)
What are centromeres made up of?
Repetitive DNA sequences
How are negatively charged DNA neutralised?
Positive charged histone proteins
Advantage of DNA packing
Inactive DNA can be folded into inaccessible locations until required
What is chromosome analysis?
Chromosome analysis is a test to look at the chromosomes in a sample of cells.
What can chromosome analysis help with?
Identify genetic abnormalities as the cause of a condition or disease.
The test can count the number of chromosomes present, and look for any structural abnormalities in the chromosomes.
What is G-banding?
A technique used in cytogenetics to produce a visible karyotype by staining condensed chromosomes.
What does G-banding allow?
Allows each chromosome to be identified by its characteristic banding pattern
How is G banding carried out?
Treating aged metaphase preparations with a protease (trypsin) before Giemsa stain is applied to generate a reproducible banding pattern.
What does FISH do?
A procedure that creates a map of the genetic material in human cells.
What can FISH analysis be used for?
Understanding a variety of chromosomal abnormalities and other genetic mutations
What are the types of FISH probes?
Unique sequencing probes
Centrometric probes
Telomeric probes
Whole chromosome probes
What are centromeric probes used for?
Determining chromosome number
What are telomeric probes used for?
Detecting subtelomeric rearrangements - often present in children with unexplained mental retardation
What are whole chromosome probes?
Cocktail of probes covering different parts of a particular chromosome - used with different fluorescent dyes
What are whole chromosome probes used for?
Detecting translocations and rearrangements
What are structural abnormalities in chromosomes?
Alteration in chromosome’s structure
What are deletion abnormalities?
A portion of the chromosome is missing or deleted.
What are duplication abnormalities?
A portion of the chromosome is duplicated, resulting in extra genetic material.
What are translocation abnormalities?
A portion of one chromosome is transferred to another chromosome.
What are inversion abnormalities?
A portion of the chromosome has broken off, turned upside down, and reattached.
As a result, the genetic material is inverted.
What are ring abnormalities?
A portion of a chromosome has broken off and formed a circle or ring.
This can happen with or without loss of genetic material.
What are the two types of translocation?
Reciprocal
Robersonian
What happens in a reciprocal translocation?
Segments from two different chromosomes have been exchanged.
What happens in a Robersonian translocation?
An entire chromosome has attached to another at the centromere.
What are the two types of chromosomes?
- Sex chromosomes, which determine male or female gender
- Autosomes, which are all ofthe other chromosomes (chromosome pairs 1 through 22) or non-sex chromosomes
