human genome & disease Flashcards
what are mutations?
mutations are permanent changes to the DNA sequence
where can you get mutations from?
mutations can be inherited or acquired
what are germline mutations?
germline mutations are things that are inherited
how are germline mutations formed?
they are passed on via the gametes (eggs
and sperm)
how are mutations acquired if DNA gets damaged or is copied incorrectly
through somatic cells
are somatic mutations passed onto the next-gen?
not passed to the next generation
what is a driving force for evolution?
Genetic variations/mutations are a driving force for evolution
What do mutations do?
- 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
what can the outcome of a mutation can also depend on?
- Environmental effects (e.g. diet, exposure to toxins)
- Other genes (‘genetic background’)
what are 2 ways to classify mutations?
- Dominant vs Recessive
- Loss of function vs Gain of function
are humans and eukaryotes diploid or haploid?
diploid
what does diploid mean?
That means they have two copies of each of their genes (one maternal, one paternal).
mutations are also known as…
alleles
are mutations heterozygous or homozygous?
A mutation (allele) can be either heterozygous (one mutant, one wildtype allele) or homozygous (both alleles mutant)
what does the dominant mutation cause?
the dominant mutation is one that causes a phenotype when heterozygous
what does the recessive mutation cause?
a recessive mutation is one that causes a phenotype only when homozygous
what must happen for a mutation (allele) to have a phenotype?
For a mutation (allele) to have a phenotype, it must affect the function of a gene.
what is a ‘Loss of function’ mutation?
A mutation might break a gene to cause it to not work as well as normal, or not work at all
why is loss of function mutation often recessive?
because a normal copy of the gene exists on the other chromosome which can replace the lost function
what is a ‘Gain of function’ mutation?
Sometimes a mutation can cause a gene to work too well, or to do something unexpected
why is a gain of function mutation often dominant?
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
how to determine if something is dominant or recessive?
- By examining the inheritance pattern of an allele
- it is X-linked, Y-linked, or autosomal
what does a line through a pedigree square or circle mean?
they died
mutation is a
loss of function
what does circles and square mean in a pedigree chart?
circle = female
square = male
what are the characteristics of autosomal recessive?
- not seen in every gen of affected family
- passed on by asymptomatic carriers
- both males and females equally likely to inherit
what are the characteristics of autosomal dominant?
- commonly in a pedigree
- affected individual – affected parent
- both males and females equally likely to inherit
what are the characteristics of autosomal dominant?
- commonly in a pedigree
- affected individual – affected parent
- both males and females equally likely to inherit
what are the characteristics of x-linked recessive?
- fathers cannot pass x linked traits to sons
- no male-male transmission
- most often affects males
how to determine inheritance patterns?
- examine the pedigree
- look for individuals that break the rules of characteristics
- identify careers that do not have this condition (if none then condition is dominant)
- find an inheritance pattern that explains the disease occurrence in a pedigree
what is happening if carriers do not have the condition?
if none of the carriers have the condition then it is dominant
what is polygenic disorder?
Polygenic disorders involve several genes acting together or environmental factors interacting with genes.
what happens when disorders appear to have a genetic basis but do not follow
straightforward inheritance patterns?
they turn into Polygenic disorders
does having a disease-related variation mean
you will get the disease?
no, these diseases come about through a combination of variants and the environment
what are most genetic disorders?
probabilistic, not deterministic
what is probabilistic?
based on or adapted to a theory of probability; subject to or involving chance variation
what does the inheritance of trait in a pedigree tell us?
The inheritance of a trait in a pedigree can tell us a lot about the location and sort of mutation.
how are simple diseases caused?
Simple diseases are 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 - X-linked recessive
- Huntington’s disease - autosomal dominant
- Cystic fibrosis - autosomal recessive
