Lecture 24 Flashcards
Mutations
- mutations can be inherited or acquired
- mutations are permanent changes to the DNA sequence
- mutations that are inherited are called germline mutations and are passed on via the gametes (eggs and sperm)
- mutations can also be acquired by somatic cells if DNA gets damage or is copied incorrectly - somatic mutations are not passed to the next generation
- the molecular bias of a mutation often is not consistent
Can be dominant / reccessive or loss of function/gain of function
What do mutations do?
- genetic variations/mutations are a driving force for evolution
- mutations can have a beneficial effect, no effect, or a deleterious (damaging or harmful) effect on the organism
- the vast majority of mutations have no effect at all
- the outcome of a mutation can also depend on
- environmental effects
- other genes
Alleles
- mutations in a single gene can have different effects
- recessive and dominant
- two copies of each gene in human, diploid
- a mutation (allele) can thus can be either heterozygous (one mutant, one wild type)
- or homozygous (both alleles mutant)
- a dominant mutation is one that causes a phenotype when heterozygous
- a recessive mutation is one that causes a phenotype only when homozygous
Loss of function mutation vs gain of function
- for a mutation (allele) to have a phenotype, it must affect the function of a gene
- a mutation might break a gene to cause it to not work as well as normal or not work at all
- somethings a mutation can cause a gene to work too well, or to do something unexpected
Loss of function
Loss of function mutations are often recessive, because a normal copy of the gene exists on the other chromosome which can replace the lost of function
Gain of function
Gain of function mutations are often dominant, because having an allele that works too well or does something novel, will not be replaced by the normal copy of the gene
Table
Finding potential disease genes
Polygenic disorders
- most dissorders appear the have genetic bias but do not follow straightforward inheritance patterns
- polygenic disorders involve several genes acting together or environmental factors interacting with genes
- Examples include: obesity, diabetes, athritis, gout, bipolar disorder
- identifying genes associated with polygenic disorders is very hard
Genetic determinism
- for most diseases, having a disease-related variation does not mean you will get the desease
- such diseases come about through a combination of variants and the environment
- different sufferers may have different disease mechanisms
- most genetic disorders are probabilistic, not geterministic
- this is also true of most traits with a genetic component, your genes do not direct your destiny
Different ways mutations can be classified
- dominant vs recesssive
- loss vs gain of function
What does the inheritance of a trait in a pedigree tell us
- location and sort of mutation
What are simple diseases ultimately caused by
Loss or alteration of the structure of the protein that is coded for by the gene
Examples of single gene disorders
- Haemophilia A/B - recessive
- Huntington disease - autosomal dominant
- cystic fibrosis - autosomal recessive
- most disorders are influenced by multiple genes and the environment
- genetics is probabilistic not deterministic
