Inheritance Patterns Flashcards
What is aneuploidy?
Having an abnormal number of chromosomes in a haploid set
What is Chromosome 22q11 Deletion syndrome?
- Also called DiGeorge syndrome
- Prevalent 1 in 4-6,000 cases
- characteristic facial features
What can go wrong with mitochondrial inheritance?
- All the mitochondria is inherited from the mother
what is imprinting?
One allele active, the other is inactive
What is mosaicism?
Somatic mosaicism= genetic fault present in only some tissues in the body (in one cell, allele normal functioning, in another may have mutation)
What is Mendel’s Law?
He deduced that genes come in pairs and are inherited as distinct units, one from each parent
How does Mendel’s Law apply to segregation?
Allele pairs separate/segregate randomly from each other during meiosis - each reproductive cell has a single allele for each trait
What is independent assortment?
traits are transmitted to offspring independently of one another
What is allelic heterogeneity?
- Different mutations within the same gene result in the same clinical condition e.g. cystic fibrosis
- Thus an individual with an autosomal recessive may be a compound heterozygote for two different mutations
What does autosomal recessive look like?
- Homozygous state
- requires 2 defected genes
- Males/females equally affected
- Affected individuals are only in the single generation
E.g. cystic fibrosis
What are the outcomes/chances with autosomal recessive?
- Chance of having = 25%
- Chance of being a carrier = 50%
- Chance of affected child’s sibling being a carrier = 66.6%
What is Consanguinity?
Reproductive union between two relatives
What is autozygosity?
Homozygosity by descent e.g. inheritance of the same altered allele through 2 branches of the same family
What does autosomal dominant inheritance look like?
- Disease manifests in heterozygous state
- Males/females affected equally
- Affects multiple generations
- Transmission from both sexes to both sexes
- Both parents can sometimes be unaffected E.g.
Gonadal mosaicism (don’t have genes for it) - Mother has reduced penetrance
- Mother has variable expression
What is the chance of an offspring affected in autosomal dominant inheritance?
Only one defected gene needed = 50% chance offspring affected
E.g. Huntington’s Disease
What is penetrance?
Percentage of individuals with a specific genotype showing the expected phenotype
What is expressivity?
Refers to the range of phenotypes expressed by a specific genotype
What is anticipation?
When a nucleotide is passed on through generations, it can get bigger and so more chance of a genetic disorder
What does X-Linked inheritance look like/ caused by?
- Caused by mutation on the X chromosome
- Never male to male – sons always get X chromosome from mother
- All daughters from affected males are carriers
- Transmitted usually through unaffected female
- Can be recessive ( Duchenne’s muscular dystrophy) or dominant (Alport’s Syndrome)
What are some genetic causes of disease?
Individually rare, but cumulatively enough to have regional genetic services
Eg: Down syndrome, Cystic Fibrosis, Huntington’s, Haemophilia
What are some multifactorial causes of disease?
Combination of genetic and environmental. Main cause of disease in developed countries
Eg: Spina bifida, Cleft palate, Diabetes, Schizophrenia
What are some environmental causes of disease?
Main causes of disease in third world and A & E (genetics play small role)
Eg: Poor diet, Infection, Drugs, Accident
