Chromosome abnormalities Flashcards
What are three different forms of chromosome abnormalities
Numerical
Structural
mutational
What is the most common numerical chromosome
Trisomy (extra chromosome)
What is a chromosomal monosomy abnormality and an example
One less chromosome
eg Turners 45x
Where does most numerical abnormalities occur
Non disjunction in meiosis
and Unbalanced Robertsonian translocation
What is caused by a trisomy of 21
Down syndrome
What is Patau syndrome
47 + 13
Mental retardation
What is Edwards syndrome
47 + 18
development problems
What is sex linked numerical abnormalities and what genders display them
Males - Kinefelter syndrome 47 XXY
Females - Turner syndrome 45 X
both cause infertility
What can structural abnormalities be due to
Transloction
Deletions
Insertions
Inversions
What are the different translocations
Reciprocal either balanced or unbalanced
Robertsonian
What is the difference between balanced and unbalanced rearrangement
Unbalanced rearrangment results in partial trisomy
as there is an unequal copy of information between the two new derivatives formed
What is reciprocal translocation and where would this most likely occur in cell division
involving breaks in two chromosomes with formation of two new derivative chromosomes
chiasma at metaphase
How can unbalanced translation occur
If normal chromosome parent combine with chromosome of parent 2 with balanced translocation
What happens in Robertsonian
fusion of two acrocentric - where the centromere is located quite near one end - chromosomes resulting in two combined chromosomes
How does robertsonian translocation cause trisomy and monosomy
As the fused acrocentric chromosome means there is either extra or less chromosome material passed on from unbalanced gametes to form trisomy/monosmy zygotes
What are the two forms of inversion and whats the difference
paracentric inversion -
pericentric inversion - involves centromere
What are the five acrocentric chromosomes
13 14 15 20 21
What happens in deletion
there is a break in the chromosome
What can a genetic mutation either be
somatic or germline
Define polymorphism
Change in genotype but to phenotypic effect
What are four types of coding mutations
silent - Base change but codes for same amino acid
missense - base changes and codes for new amino acid
nonsense - base change causes a stop to process i.e. codon prevent amino acid being formed
frameshift - either deletion or insertion of a base
What is point mutation of base pair of a purine to purine called
Transition
What is a point mutation of a Purine to pyrimidine called
Transversion
What are five methods of detecting mutations
Polymerase chain reaction (PCR)
Gel electrophoresis
Restriction fragment length polymorphism (RFLP) analysis
Amplification refractory mutation system (ARMS)
DNA sequencing
What is needed for PCR
DNA polymerase
DNA
Nucleotides
What are the steps of PCR
- Denature (high temp)
- Anneal (low temp)
- extend (70-75 temp)
- Gel electrophoresis
What does Gel electrophoresis do
Separate DNA fragments by size
What is the movement of DNA in Gel electrophoresis
DNA negatively charged, applying an electric field moves to positive charge
What is the advantages of PCR and Gel electrophoresis
Speed
Ease of use
Sensitive
Robust
How is ARMs applied
PCR reaction using fluorescent primer either wild type or mutant to see if mutation present, if present with mutant primer causes amplification
What is Restriction endonucleases
Enzymes from bacterial cells that cleave DNA
What does RFLP use (restriction fragment length polymorphism)
Restriction endonuclease cutting PCR DNA,
How do we know it mutant present using RFLP
If mutant fragment present will show up on restriction digest assay
What can RFLP used to diagnose?
sickle cell anaemia
In DNA sequencing what is a chain terminated by
dideoxynucleotides
How do dideoxynucleotides terminate a DNA sequence
DNA polymerase cant recognise them so chain is stopped
What is the least suitable method for detecting whether an individual is a carrier of sickle cell anaemia
Karyotyping
Why cant a karyotype show a point mutation
as shows whole chromosome
