Genes and Disease I Flashcards
What is a genetic disease?
How do we inherit genetic disorders?
How do genetic mutations occur?
- Any disease caused by an abnormality in the genetic makeup of an individual.
- Some people inherit genetic disorders from the parents, while acquired changes or mutations in a preexisting gene (monogenic) or group of genes (multifactorial) cause other genetic diseases, Chromosomal abnormalities
- Genetic mutations can occur either randomly or due to some environmental exposure.
What are monogenic diseases?
What are the 3/4 main categories?
-modifications in a single gene occurring in all cells of the body
* Dominant
* Recessive
* X-linked
* (Mitochondrial)
What is the structure of a gene? Label.
1- What is the genetic code?
2- How is the nucleotide sequence read?
1- The set of rules that specify how the nucleotide sequence of mRNA is translated into the amino acid sequence of a protein
2- As triplets called codons
- The first letter is the 5’ end and the last letter is 3’ end
Why is the genetic code described as:
-specific
-universal (nearly)
-redundency/degenerate
-non-overlaping
-specific: A specific codon always codes for the same amino acid e.g. CAG always codes for Glutamine
-universal: Applies to all species - nearly universal because some differences have been identified in the codons used in mitochondria
-redundency/degenerate: A given amino acid can be coded for by several different codons
(codons generally differ at the 3rd base, known as wobble base)
-non-overlaping: Code is read from a fixed starting point as a continuous sequence of bases - each nucleotide is part of only one codon
1- What is the open reading frame?
2- How is the reading frame determined?
True/False In Protein sysnthesis only 1 ORF contains useful info?
1- A set of codons that run continuously, bounded by an initiation codon (at the 5’ end) and a termination codon (at the 3’ end)
2- By the start codon (AUG) - subsequent nucleotides are read in sets of three
TRUE
1- What causes frame shift mutation?
2- What causes a base substitution/point mutation?
Give examples
What is the antisense strand?
- DNA strand which acts as the template for mRNA transcription
How does a point/substitution mutation cause:
-Mis-sence
-Silent
-Nonsense
-Mis-sence:
* Point mutations only affect a single codon - Mis-Sense Mutation.
* Their effects may not be serious unless they affect an amino acid that is
essential for the structure and function of the finished protein molecule (e.g. sickle cell anaemia)
-Silent:
* No change in codon.. degenerate nature
-Nonsense:
* Codes for STOP CODON! .. truncated protein
What is the wobble hypothesis?
The phenomena that explains why multiple codons can code for a single amino acid
One tRNA molecule can recognise and bind to more than one codon due to the less precise base pairs that can arise between the 3rd base of the codon and the base at the 1st position of the anticodon
What are the two different ways that point mutations/substitutions can be defined?
- – Transitions: Purine → purine or Pyrimidine → pyrimidine
- – Transversions: Purine → pyrimidine or Pyrimidine → purine
What is an inversion mutation?
- A mutation where two DNA base pairs are switched around - only affects a small part of the gene
How do additions and deletions work to cause a frameshift?
- number of bases added or deleted is not a multiple of three
> reading frame being shifted so that a completely different set of codons are read beyond the point where the mutation starts
What is autosomal dominant inheritance?
- An affected individual has an affected parent
> Autosomal - the gene is located on one of the 22 non-sex chromosomes
Dominant - one allele results in the associated phenotype (the trait will be expressed in both heterozygous and homozygous genotypes; however homozygosity is statistically very unlikely)
What is autosomal recessive inheritance?
- Only affects individuals in 1 generation not in previous or subsequent generations
> Recessive - phenotype only results when there are two copies of the allele
