L23: X-linked and mitochondrial inheritance Flashcards
Which class of genetic disorder does x-linked inheritance belong to
Single gene/ Mendelian disorder
What are the types of sex-linked inheritance
X-linked recessive
X-linked dominant
Y-linked
What is the most common type of sex-linked inheritance
X-linked recessive
Is a male with an reccessive X chromosome hemizygote or heteroyzgote
Hemizygote
Is female with one recessive X chromosome hemizygote or heterozygote
Heterozygote
What does an x-linked recessive pedigree show
- multiple generation affected
- males affected
- no male to male transmission
What are the common x-linked recessive disorders
- red-green colour blindness
- fragile x syndrome
- duchenne muscular dystrophy
- Becker muscular dystrophy
What is duchenne muscular dystrophy
An x-linked recessive disorder that is a muscle degenerative disorder which is present in the young
3 ways to investigate duchenne muscular dystrophy
- high levels of creative kinase
- absence staining with antibodies to dystrophin
- deletions and mutation in dystrophin
What are the types of mutations that occur in duchenne muscular dystrophy
- deletions
- point mutations
- premature stop codon
- altered splice site mutations
- promoter mutations
How does the mutation in duchenne muscular dystrophy lead to absence of dystrophyn protein
The mutation cause changes in the reading frame lead to absence of the protein
How does mutation in Becker muscular dystrophy lead to milder phenotype
The mutations are in frame with create partially functional dystrophyn
In duchenne muscular dystrophy does female carrier show any symptoms
Yes they do but it is very mild that is does not show any physical features
Why do females show x-linked recessive traits
- x inactivation occurs which is random and clonal
- Xq codes for XIST gene which inactivates the chromosome
What is a Barr body
This is the inactive X chromatin wrapped up and not used in a cell after x-inactivation
Why do females show x-linked recessive traits
- skewed x-inactivation
- Turner syndrome (45,x)
- homozygous for a recessive trait
- x autosome translocations
What pattern does an x-linked dominant pedigree show
- multiple generations affected
- more females affected than males
- no male to male transmission
What are the features of mitochondrial inheritance
- from mother as the sperms mitochondria is expelled at fertilisation
What is the pattern of mitochondrial inheritance on a pedigree
- female is affected: all children are affected
- affected male does not pass it on to children so no children are affected
What does the severity of mitochondrial disorder vary with
- heteroplasmy
- threshold effects
What is heteroplasmy
when a mutation arises it created a mixed population of mitochondria within the cell
What is bottleneck
When cells divide the mitochondria is partitioned randomly
Two example of mitochondrial dna disorders
- Kearns-Sayre syndrome
- MELAS
