Pattern of Genetic Inheritance Flashcards
What are the 3 classifications that diseases fall into?
- 100% environmental
- Single gene
- Polygenic
*genetically determined; environmentally determined; 1+2 types
What is Genetic diseases?
- Rare
- Genetics simple
- Unifactorial
- High recurrence rate
What is Environmental diseases?
- Common
- Genetic complex
- Multifactorial
- Low recurrence rate
What are 5 classifications of genetic disorders?
- Chromosomal aberrations
- Multifactorial (Polygenic)
- Single gene (Monogenic)
- Somatic mutations (cancer)
- Atypical Inheritance
What is Euploidy?
Normal 46 chromosomes (2n)
What is Polyploidy?
- Spontaneous abortion
2. Change in the Genome copy number (3n or 4n)
What is Aneuploidy?
- Caused by nondisjunction
2. Changing one chromosome
What is Trisomy numerical abnormalities?
- Compatible with life
2. (2n+1)=47
What is Monosomy numerical abnormalities?
- (2n-1)=45
- Two types:
a. Autosomal (incompatible with life)
b. Sex chromosomal (compatible with life)
- Abnormalities of sex chromosomes are better tolerated than autosomal
- Loss of chromosomal material is more dangerous than gain
What are 8 types of Chromosomal aberrations?
- Down Syndrome
- Edward syndrom
- Patau syndrome
- Klinefelter syndrome
- Turner syndrome
- Cri du chat syndrome (5’ deletion)
- Angelman syndrome
- Prader-willi syndrome
What is polygentic disorders (multifactorial)?
- Most common
- Influence of multiple genes + environmental
- One organ system affected
Ex: Diabetes mellitus, Hypertension, Gout, Schizophrenia
What is Monogenic Disorders?
- 1% of total live births
- Follow Mendelian type of inheritance
- Dominant/recessive pedigree patterns
What is Autosomal Recessive Inheritance Homozygotes?
- With two copies of the altered gene (autosomes) are affected
- Ex: Cystic fibrosis, Sickle-cell anaemia, Phenylketonuria, beta thalssaemia
What is Autosomal Recessive Inheritance Heterozygote?
- With one copy of altered gene and second normal gene are carrier of the disease and have no symptoms
What is Autosomal Dominant Inheritance Heterozygotes?
- With one copy of altered gene are affected
2. Ex: Polycystic kidney disease, neurofibromatosis, Huntington disease
What is Autosomal Dominant Inheritance Homozygotes?
- With both altered genes are generally die before reproductive age
What is X-linked Recessive Inheritance?
- Males are more prone due to having only one “X”
- Males can’t pass the effected X allele
- Women are very rarely affected and are primarily heterozygous carriers
EX: Duchenne Muscular Dystrophy, Hemophilia, Bruton’s Agammaglobinemia
What is X-linked Dominant Inheritance?
- Only one copy of the X allele is required to have the disease
- Both males and females can be affected
- Males are more affected; all his daughters will be affected, but not of his sons will be affected
EX: Fragile X Syndrome, Incontinentia Pigmenti
What is Somatic Mutations?
- Alternations in DNA that occur after conception
- Can occur in all cells except germ cells (which are not passed down to children)
- These alterations usually cause cancer
What is Atypical patterns of Inheritance?
- Don’t follow the rules of Mendellian pattern of inheritance
What is Co-dominance?
- Type of Atypical pattern of Inheritance
- When two allelic traits that are both expressed in the heterozygous state
- Ex: Blood group AB: the A and B blood groups are codominant
*Incomplete dominance: red flower and white flower germinate creating a pink flower (phenotype mix)
What is Pseudo-dominant Inheritance?
- When a woman is homozygous for an autosomal recessive disorder and the husband is heterozygous of the same disorder
- There is 1:2 ratio for the children to be affected
- It is not dominant but it looks like a dominant pattern
*Happens in recessive cases only
What is Atypical inheritance of single-gene disorders?
- Maternal inheritance of mitochondrial mutation
- Atypical presentation for Autosomal Dominant defects
- Genomic Imprinting
- Mosaicism
What is Mitochondrial Inheritance?
- Mitochondria comes from the mother
- mtDNA is small circular double stranded
- When disorder affects mitochondrial chromosome it affects the energy metabolism
Ex: Lebers hereditary optic neuropathy (LHON); Rapid Optic nerve death (blindness in young adult life)
What is Anticipation?
- A genetic disorder
displays an earlier age of onset and/or a greater degree of severity in successive generations of
the family pedigree. - The reason might be the gradual expansion of trinucleotide repeat within or near a coding gene
Ex: Huntington disease, CAG repeats, Myotonic dystrophy
What is Pleiotropy?
- One gene control more than one phenotype
- Different symptoms in different parts of the body can be affected by just one gene
- Ex: Tuberous sclerosis, Cystic fibrosis, Sickle cell anemia
What is Variable expressivity?
- Refers to the range of signs and symptoms that can occur in different people with the same genetic condition
* In autosomal dominant polycystic kidney disease, some individuals have renal dysfunction at early adulthood while others have not
What is Reduced penetrance?
- Certain autosomal dominant disorders in which some individuals show the sign and symptoms of the diseases while others are never clinically diagnosed (so called reduced penetrance)
- Might be due to:
a. modifying effects of other genes
b. interactions of the gene with environment factors
What is Genomic Imprinting?
- Is a genetic phenomenon by which certain genes are expressed in a parent-of-origin-specific manner
- Inheritance process independent of Mendelian inheritance
- Is due to methylation and histone modifications in the chromosome
Ex: Angelman syndrome, Prader-Willi syndrome…
What is Familial?
Transmitted in the gametes through generations
