Chromosome Mutations and Abnormalities - Second Lecture Flashcards
What are the three different types of chromosomal abnormalities?
Numerical, structural, mutational
What is the result of non-disjunction?
Two gametes with disomy (meiosis 1)
1 gamete with disomy - (meiosis 2)
What is trisomy 21 known as?
Down’s Syndrome
What is trisomy?
The addition of an extra chromosome
What is responsible for 50% of first trimester miscarriages?
Trisomy mutations
What are the features of someone with down’s syndrome?
Characteristic facial dysmorphologies IQ less than 50 Average life expectancy (50-60 years) Alzheimer’s disease in later life
What is trisomy 13 known as?
Patau syndrome Incidence: 1 in 5000 Multiple dysmorphic features and mental retardation
About 5% die within first month, very few survive beyond first year Non-dysjunction (90%), maternal origin Unbalanced Robertsonian translocation (10%)
What is Trisomy 18 known as?
(Edwards syndrome) Incidence: 1 in 3000 Severe developmental problems; most patients die within first year, many within first month
Non-disjunction (90%), maternal origin
What is 45, X mutation known as?
Turner syndrome Incidence: 1 in 5000 to 1 in 10000 (liveborn) Incidence at conception much greater, about 97% result in spontaneous loss
Females of short stature and infertile Neck webbing and widely spaced nipples Intelligence and lifespan is normal Female because there is no Y chromosome
What is 47,XXY mutation known as?
(Klinefelter syndrome) Incidence: 1 in 1000 Tall stature, long limbs Male but infertile, small testes, about 50% gynaecomastia Mild learning difficulties
What are the terms used to describe complete or incomplete retention of DNA during a mutation?
Balanced or unbalanced
What is the definition of a balanced translocation?
There is still a complete set of DNA between the two chromosomes, if the translocation takes place in a non-critical location, there will be no major effects to the individual
What is meant by reciprocal translocation?
Involving breaks in two chromosomes with formation of two new derivative chromosomes
What are the different types of Structural abnormalities?
Deletions Insertions Inversions Translocations
What is the effect of unbalanced translocation on the gametes produced?
Production of gametes with, partial trisomy and partial monosomy, this will result in offspring with abnormal phenotypes
What are accrocentric chromosomes?
One of the arms of the chromosome is very short
What is robertsonian translocation?
When the two longer arms of accrocentric chromosomes combine, the short arms are lost and also fuse together
What does Robertsonian translocation result in
Balanced - normal gametes
Unbalanced - Trisomy and Monosomy
What is pericentric inversion?
When the inversion takes place over the centromere
What is polymorphism?
The natural genetic variation within a populaiton
What are the different types of genetic mutations?
Germline or somatic
Gene disruption /disease-associated
Polymorphism
What are the types of non-coding mutations?
Coding mutations -
Silent – synonymous e.g. CGA (Arg) to CGC (Arg) (GIVES THE SAME AMINO ACID)
Missense (A MISSENCE MUTATION IS A POINT MUTATION WHICH A SINGLE NUCLEOTIDE CHANGE RESULTS IN A CODON THAT CODES FOR A DIFFERENT AMINO ACID)
Nonsense (CODON FOR AMINO ACID IS CHANGED TO A CODON THAT CODES FOR A CHAIN TERMINATING CODON)
Frameshift – deletion / insertion
What are transitions - point mutations?
Purine to purine or pyrimidine to pyrimidine
What are transversions?
Purine to pyrimidine or vice versa
