Lecture 4 - mutation Flashcards
What is a mutation?
the process that produces a gene or chromosome set differing from that of the wild-type
What is a wild-type?
the form that predominates in nature
What are the effects of spontaneous mutation?
if not repaired, mutations will be passed down to all daughter cells - in multicellular organisms this will only be inherited by any progeny if the mutations is in the germline
What is the standard human karyotype?
46 chromosomes - 22 x 2 autosomal chromosomes
- XX or XY sex chromosomes: pair with each other
- written: 46,XX or 46,XY
What is polyploidy?
an unusual number of chromosome sets
What is triploidy?
3n
What is tetraploidy?
4n
What is monoploidy?
1n (when 2n is normal)
What is aneuploidy?
one or a few individual chromosomes extra/missing
What are 2 examples of human aneuploidies?
trisomy - 3 homologues instead of 2
monosomy - 1 homologue instead of 2
What are the 3 viable human autosomal aneuploids?
- 47, XX or XY + 13
- 47, XX or XY +18
- 47, XX or XY +21
What are the 2 sex chromosome aneuploidies?
47, XXY: Klinefelter syndrome
45, XO: Turner syndrome
What are the 3 types of large-scale chromosomal rearrangements?
Deletions - part of the chromosome is missing
Inversions - part of the chromosome has been flipped
Translocations - part of the chromosome has been moved
What are sources of mutation of individual genes differing from wild type?
mistake during replication:
- point mutations (a single nucleotide)
- small insertions/deletions –> frameshifts
genes interrupted by transposons (jumping gene)
DNA breaks incorrectly repaired
What are the 4 types of point mutations?
- Silent - no change to amino acid sequence
- Nonsense - introduction of a stop codon into the gene
- Missense - changes the amino acid sequence
- Null allele - total loss of function
What are autotrophic mutants?
mutants that are unable to synthesise essential compounds - e.g. adenine & serine
What is minimal media?
contains only the nutrients that an organism cannot synthesise for itself
What is complete media?
contains extra nutrients, for example all amino acids. This should make up for some defects in metabolic pathways and allow mutant cells to grow
What type of media can wild-type cells grow on?
minimal media & complete media
What type of media can auxotrophic mutants grow on?
complete media OR minimal media supplemented with specific molecule they are unable to make
- they cannot grow on normal minimal media
What does ‘+’ denote in genetic nomenclature?
wild-type
How are gene names written?
in italics
What are genes often named after?
the phenotype of a null allele
Can either allelic mutants or non-allelic mutants grow on minimal media?
No - they are unable to complete the biosynthetic pathway
