Genetic Mutations Flashcards
Diploid organism
- two sets of chromosomes
- two alleles of each particular gene
- mutations usually result in recessive alleles
- expressed only in the homozygous condition unless the mutation is on the X chromosome
Homozygous
The two alleles are the same; the organism is homozygous for that gene
Heterozygous
- the two alleles are different; the organism is heterozygous for that gene
- the dominant allele May mask the recessive gene
If an organism is haploid (one set of chromosomes)
Recessive alleles are not masked by dominant alleles
Genotype
Genetic composition of an organism
Phenotype
Measurable physical and biochemical characteristics of an organism (whether desirable or not)
Gene mutations
- changes in the nucleotide base sequence in a gene
* can result in non-functional proteins, including non-functional enzymes
Types of gene mutations
- substitution
- deletion
- addition
- duplication
- inversion
Substitution
- replacement of one nucleotide with another containing a different base
- missense
Deletion
• loss of a nucleotide
Addition
- aka insertion
* addition of an extra nucleotide
Duplication
• repetition of a portion of a nucleotide sequence within a gene
Inversion
• reversal of the portion of the nucleotide sequence in the gene
Sickle cell anaemia
- inherited condition that results from a substitution
* RBC sickles in low O2 areas
Mutations can be…
Disadvantageous, neutral or beneficial
Disadvantageous mutations
- because DNA is non-overlapping
- frameshifts
- lack of a start codon/change in position
- codon changed into a stop codon (nonsense)
Frameshifts
• addition and deletion
Where do neutral mutations often occur?
In the introns
Describe neutral mutations
- DNA is degenerate -> different codon but it codes for the same AA; protein structure is unaffected
- a different codon causes a different amino acid, but if it is not at an essential site on the polypeptide chain, it is possible that the change in amino acid could have no effect on protein structure
- think about where bonds form, and how this affects reactions and functions
Beneficial mutations
- change the phenotype so the organism has a better chance of surviving and reproducing
- they are very rare, but inevitable in a population large enough
- ultimate source of all variation
- raw materials for the evolution of a new species by natural selection
