genetics Flashcards
When does DNA replication occur?
During S phase
Define polymorphism
Any variation in the human genome that has a population frequency of greater than 1% or any variation in the human genome that doesn’t cause a disease in its own right but may predispose to a common disease
How is a chromosome recognised?
- banding pattern with specific stains
- position of centromere
- length
Describe balanced chromosome rearrangement
All the chromosomal material is present but in a rearranged order
Describe unbalanced chromosome rearrangement
Extra or missing chromosomal material, usually 1 or 3 copies of some of the genome
What is aneuploidy?
Whole extra or missing chromosome
Describe translocation
Rearrangement of chromosomes
Describe robertsonian translocation
Two acrocentric chromosomes stuck end to end, increased risk of trisomy in a pregnancy
What occurs in trisomy 14?
Miscarriage
What occurs in trisomy 21?
Down syndrome
What occurs in trisomy 19?
Edwards syndrome 47XY +18
Why is x chromosome aneuploidy better tolerated by woman?
Due to X inactivation
What does array CGH detect?
Any size of imbalance
Where do new mutations occur?
In gametogenesis
What occurs if the mutation is post-zygotic?
The child would be mosaic
Describe mosaicism
Different cells have different genetic constitution, this could be a mosaic chromosome abnormality or mosaicism for a point mutation
What could chromosome changes cause?
- activate an oncogene
- delete a tumour suppressor
Only 2-3% of the genome is exons, what are the rest involved with?
- regulation of genes
- space genes out
- insulates genes from promotors
- provides substrate to expand genome/ add genes
What occurs as a result of a promotor mutation?
No or reduced transcription
No or reduced protein
Define penetrance
The likelihood of having a disease if you have a mutation. 100% penetrance means you will always get the disease if you have the mutation
What are mendelian disorders?
Disease that segregate in families in the manner predicted by mendels law. A disease that is predominantly caused by a change in a single gene, high penetrance
Describe autosomal dominant
One faulty copy of the gene causes the disease. Disease is seen in all generations
Describe autosomal recessive
Two faulty copies of the gene to cause disease, 1 in 4 chance of inheriting the faulty gene
Describe the genetics of Huntington’s disease
- 100% penetrance
- autosomal dominant
Describe x-linked inheritance
Gene fault lies on the x chromosome. A female carries a mutation but will not show major features of the disease
Describe x-inactivation
In female cells only on x chromosome is active, so in some cells the affected x chromosome is expressed and then in other cells the normal x chromosome is expressed
What are single nucleotide polymorphisms?
Alterations in DNA sequence, snps must exert effects that are not in themselves a disease. Most snps have no effect
Describe copy number variations
Extra or missing stretches of DNA, highly prevalent in the genome, deletions or duplications
