GENETICS - Mutations and Defects Flashcards
Red-Green defects are in which disease?
acquired optic nerve disease (except glaucoma and autosomal dominant optic atrophy)
What are the main examples of trinucleotide repeat disorders? (7)
- Fragile X syndrome
- Friedrich’s ataxia
- Machado-Joseph ataxia
- Spinocerebellar ataxia
- Spinobulbar muscular atrophy
- Myotonic dystrophy
- Huntington chorea
Blue-yellow defects are in which disease
Acquired retina disease (except cone dystrophy and Stargardt’s)
Which mutations causes MEN 2a and MEN2b?
RET proto-oncogene on chromosome 10
What is a mutation? What external factors can cause a mutation?
any permanent change in DNA
1) Ionising radiation
2) Chemicals
3) UV light
What are the three types of point mutations?
1 - missense mutation - different amino acids are transcribed altering the sense of the code (haemoglobinopathies
2 - nonsense mutation - mutation leads to premature stop codon - NF type 1
3 - splice mutation - mutation alters a critical splice junction
What examples are there for triplet expansion diseases? What phenomenon do they cause. (4)
Increased number of trinucleotide repeats –> number of repeats can increase across generations, called anticipation.
- myotonic dystrophy (CTG repeat in DMPK gene on chromosome 19)
- Fragile-X (CGG repeat in FMR1 gene)
- Huntington’s (CAG repeat in HTT gene)
- Spinocerebellar ataxia (CAG expansion)
- Freidrech’s ataxia (GAA expansion in FXN gene)
CAG = craving glutamine
CGG = fragile, can’t grow grey matter
CTG = can’t tie genes
GAA = gaa! Ataxia awful.
What examples are there of microdeletion syndromes? (3)
- Prader Willi (Chromosome 15)
- Williams syndrome (Chromosome 7)
- Di George (Chromosome 22)
Consanguinity is more likely to have which type of inheritance?
Recessive
What is a Robertsonian translocation?
a chromosome rearrangement where the two long arms of two acrocentric chromosomes (non central centromeres) fuse to form a single chromosome - leading to loss of the short arms
How many chromosomes do robertsonian individuals have? what is their risk of trisomy in offspring?
- 45 chromosomes (normal phenotype)
- increased risk
What is lyonisation? What does it give rise to in terms of expression?
Lyonisation is a physiological process where one of the two X chromosomes in cells of a female is inactivated during embryonic development (male/female X chromosome is randomly affected).
gives rise to patchy expression of X-linked mutations in female carriers
What chromosome carries the blue pigment gene?
Chromosome 7
How does aneuploidy (abnormal numbers) occur?
usually in Non-disjunction during meosis I
How do structural changes in chromosomes occur and what is the difference between balanced and unbalanced recombination?
structural changes occur due to breakage followed by a recombination that is abnormal.
Balanced recombination results in chromosomes with normal amount of genetic information
Unbalanced recombination occurs when there is loss or gain of genetic material