Modes of inheritance Flashcards
How many pairs of chromosomes are in the human body?
23 pairs
What does mitochondrial DNA encode?
15 proteins
rRNA
tRNA
Where is mitochondrial DNA inherited from?
All mitochondrial DNA is inherited from mother
What are complex genetic disorders?
Acquired both genetically and environmentally
Why are brown eyes dominant?
Gene which regulates eye colour is OCA-2
It controls the amount of melanin in melanocytes
Active OCA-2 allows melanins to build up in melanocyte so you get brown eyes
Gene encoding blue eyes is inactive OCA-2 so no melanin produced
HERC2 controls the activity of OCA-2. You ned to have active HERC2 as well as active OCA-2 to have brown eyes
Active OCA-2 and inactive HERC2 = blue eyes
What characteristics do autosomal dominant disorders have?
Gain in function- gene makes a protein with a new function
Dominant negative effect- mutated form interferes with activity of protein it binds
Insufficient- mutant gene results in 1/2 amount of a protein- not enough for normal function
What is a carrier?
Carriers of recessive diseases have at least 1 copy of a gene but the normal one is sufficient to maintain normal function
What characteristics do autosomal recessive disorders have?
Loss of function
What causes cystic fibrosis?
Defective chloride ion channel
Caused by a mutation in gene encoding chloride ion channel- CFTR (cystic fibrosis transmembrane conductance regulator) gene on chromosome 7
Loss of function
What are symptoms of cystic fibrosis?
Impaired airway defence
Prone to respiratory infection
Digestive issues e.g. Meconium ileus (bowel obstruction due to thick, sticky intestine)
Who does x-linked recessive disorders affect?
Affects mainly males
Females can be carriers or affected (homozygous)
What is an example of an x-linked recessive disorder?
Haemophilia- affects mostly males
In some cases, female carriers exhibit subtle signs of the disease e.g. Fabry’s disease
How does an x-linked dominant pattern appear on a pedigree?
Similar to autosomal dominant
All daughters and no son’s of affected father are affected
What is an example of an x-linked dominant disease?
X- linked Hypophosphatemia
Caused by PHEX gene mutation
Leads to overproduction of FGF21- FGF21 inhibits kidney phosphate resorption so kidneys can’t retain phosphate. Results in vit. D- resistant rickets
How does a Y linked disorder present on a pedigree?
Vertical transmission
All sons of affected father affected
Affects only males
What are examples of Y linked disorders?
Retinitis pigmentosa
Y- linked mutation in RPY gene
Cells of retina produce a defective protein
What is special about mitochondria?
Have their own DNA
Shared an evolutionary past with bacteria- endosymbiosis
What are mitochondrial proteins encoded by?
Majority of mitochondrial proteins encoded by nuclear genes
How does mitochondria replicate?
By binary fission
Can lose or gain mutated genes
Mitochondria undergo random segregation
Why are mitochondrial diseases variable?
Mitochondria have multiple copies of their genome- some are normal, some mutant (this is known as heteroplasmy)
Disease symptoms are only expressed above a threshold
What determines the severity of symptoms in a mitochondrial disease?
The number of affected mitochondria
The number of mutant mitochondria can change with time
Symptoms develop with age due to an accumulation of mutant mitochondria
What is an example of a mitochondria disease?
Leber’s hereditary optic neuropathy (LHON)
Visual loss in young adulthood, degeneration of optic nerve and retina
Typically in males, occasionally females
