17 Modes of inheritance Flashcards
How many DNA chromosomes to bacteria usually have?
Only 1 (compared to 23 pairs found in humans)
How do bacteria divide?
Binary fission (asexual)
Roughly how many genes are encoded by bacterial genomes?
4,000-6,000
What does each gene encode for?
An mRNA
What does each mRNA encode for?
One protein
What does homozygous mean?
Two identical copies of an allele for that gene
What does heterozygous mean?
Two different alleles for a particular gene
What is a locus?
A single position of a gene on the chromosome
How many autosomal pairs do humans have?
22
How many chromosomes do humans have?
46
Roughly how many genes do humans have?
25,000
How many different types of single gene disorders are there?
~4,000
Most common ~1/500
What is a dominant autosomal characteristic?
A characteristic is dominant if it manifests in a heterozygote
Characteristics of dominant autosomal diseases
- Multiple generations affected
- Each affected person normally has one affected parent
- Child of affected person has 1 in 2 chance of being affected
What pattern is seen in dominant autosomal disorders?
Vertical pedigree pattern
How many people are affected by Huntington’s disease?
1 in 20,000 (UK)
What are the symptoms of Huntington’s disease?
- Start at 30-50 years
- Difficulty concentrating
- Depression
- Stumbling
- Involuntary jerking
What mutation causes Huntington’s disease?
DNA expansion of a CAG repeat on chromosome 4
What does the mutation in Huntington’s cause?
Abnormal intracellular Huntington protein aggregate becomes toxic to neurons resulting in cell death
How many people are affected by osteogenesis imperfecta (brittle bone disease)?
1 in 15,000
What are some symptoms of osteogenesis imperfecta?
- Bones break easily
- Mild to severe
- Hearing loss
- Breathing problems
- Short height
What causes type I osteogenesis imperfecta?
Insufficient quantities of collagen
What causes type II, III and IV osteogenesis imeprfecta?
An abnormal protein with an altered structure interferes with the function of the normal protein
What do dominant autosomal disorders tend to be?
- Gain-of-function (protein with new function made)
- Dominant negative effect (interference with activity of proteins it binds)
- Insufficient (1/2 amount of a protein produced, not enough for normal function)
What is a carrier?
Someone that has lost a single copy of a gene but the normal one is sufficient for normal function
What does recessive mean?
Two copies of the abnormal gene need to be present for the disease or trait to develop
Recessive disorders tend to be…
Loss of function mutations (deletions)
What pattern is seen in recessive autosomal disorders?
Horizontal pedigree pattern
How many people are affected by cystic fibrosis?
1 in 3,000 newborns
What are some symptoms of cystic fibrosis?
‘Failure to thrive’
- Prone to respiratory infections
- Digestive issues
What mutations cause cystic fibrosis?
Various mutations in gene encoding chloride ion channel (CFTR gene on chromosome 7)
What does the cystic fibrosis mutation cause?
Defective chloride ion channel
- Loss of function, degraded faster
What highly raises the risk of autosomal recessive diseases?
Consanguineous marriages
Why are X-linked diseases more impactful on sons?
They only have one copy of the X chromosome
Give an example of an X-linked recessive disorder where carriers exhibit subtle signs
Fabry’s disease
Give an example of an X-linked recessive disorder
Haemophilia (frequent, severe bleeds -> Factors VIII or IX)
Main trend in X-linked recessive disorders
All daughters of a man with the disorder will be carriers
Main trend in X-linked dominant disorders
All daughters and no sons of an affected father are affected
Give an example of an X-linked dominant disorder
X-linked hypophosphatemia
What does X-linked hypophosphatemia cause?
- Kidneys can’t retain phosphate
- Vitamin D resistant rickets
What gene mutation causes X-linked hypophosphatemia ?
XLH gene mutation resulting in inactivity og PHEX protein
Main trends in Y-linked disorders
- Only affects males
- All sons of affected father
- Vertical pedigree pattern
Example of Y-linked disorder
Retinitis Pigmentosa
What mutation causes retinitis pigmentosa?
Mutation in RPY gene
What does the RPY mutation cause?
Cells of retina produce a defective protein
Key facts about mitochondria
- Share evolutionary past with bacteria
- Have their own DNA (also use proteins encoded by nuclear genes)
Main trend in mitochondrial disorders
Maternally inherited
Why is there a variable phenotypic pattern with mitochondrial disorders?
Different cells have different numbers/complements of mitochondria
What factors affect the severity of symptoms concerning mitochondrial disorders?
- Amount of WT (wild type) to mutated mtDNA
- Severity of mutation
Give an example of a mitochondrial disease
Leber’s hereditary optic neuropathy (LHON)
What symptoms are common of LHON?
- Visual loss in young adulthood
- Mutations disrupt function of mitochondria (oxidative phosphorylation)
