L3: Modes of Inheritance Flashcards
Modes of Inheritance
- Mendelian inheritance (single gene traits)
- Multi-factorial inheritance
- Non-traditional inheritance
Def of Mendelian Inheritance (Single Gene Traits)
- The inheritance of single-gene disorders
Def of Locus
Specific position of gene on the chromosome
Def of Alleles
Introduction to Genetic Pedigree
Types of Mendelian Inheritance
Def of AD Inheritance
Risk of Transmission in AD Inheritance
Rules of AD Inheritance
…
Sex affected in AD Inheritance
Male & Female are affected in equal proportion
Generations affected in AD Inheritance
- Transmitted from one generation to the next
- Sporadic cases with high paternal age suggest new mutation
Transmission between sexes in AD Inheritance
- All forms of transmission between sexes are observed (male to male - male to female // female to female - female to male)
- Male to male transmission exclude the gene on X chrom
Examples of AD Inheritance
Sporadic cases with AD disorders suggest ……..
New Mutation
Male to Male transmission exclude ……..
X-Linked Inheritance
Def of AR Inheritance
Risk of Transmission in AR Inheritance
Sex affected in AR Inheritance
Male & Female are affected in equal proportion
Generations affected in AR Inheritance
Affected individual usually only in a single generation
Consanguinity supports …….
AR Inheritance
Examples of AR Inheritance
Factors affecting AD Gene Expression
- Pleiotropy
- variable Expressivity
- Reduced penetrance
- New Mutations
Def of Pleiotropy
A single gene (AD) that may give rise to two or more apparently unrelated effects.
Etiology of Pleiotropy
- Different mutations in the same gene
Examples of Pleiotropy
In tuberous sclerosis, some affected individuals may have all features (learning difficulties, epilepsy, facial rashes,…)
Def of Variable Expressivity
- Striking variation in the clinical features of AD disorders from person to person, even in the same family.
Examples of Variable Expressivity
PCKD
Def of Reduced penetrance
Penetrance describes the frequency with which phenotypic manifestation of a gene are expressed.
Examples of Reduced penetrance
Def of New Mutations
- AD disorders sometimes appear in a child of unaffected parents because of a spontaneous mutation
Etiology of New Mutations
- May be associated with advanced paternal age
Examples of New Mutations
- About 80% of patients with achondroplasia have experienced a mutation in (FGFR3) gene.
Difference between penetrance & Expressivity
Pseudodominance Inheritance
Co-dominance Inheritance
Incomplete Dominance
Types of Sex Chromosome Inheritance
- X Linked Inheritance
- Y Linked Inheritance
Types of X-Linked inheritance
- XL Dominant
- XL Recesive
- Sex Controlled
- Sex Limited
X-Linked Dominant Inheritance
- Whci sex is more affected?
- Females are affected more frequently than males
- Females are affected less severely than males
X-Linked Dominant Inheritance
- Transmission between sexes
- Affected female can transmit the disorder to both male and female offspring
- Affected males can only transmit the disorder to their daughters but not sons.
In X-Linked Dominant Inheritance
- Affected males can only transmit the disorder to …..
their daughters but not sons.
Examples of X-Linked Dominant Inheritance
- Hypophosphatemic rickets
- Incontinentia pigmenti
Def of X-Linked Recessive Inheritance
- An x-linked recessive trait is one determined by a gene carried on the X chromosome and usually only manifest in males
Risk of Transmission in X-Linked Recessive Inheritance
Risk of Transmission in X-Linked Recessive Inheritance
- Male affected married normal female (Hemophilia)
- All daughters obligate carriers
- All sons normal
Risk of Transmission in X-Linked Recessive Inheritance
- Carrier female (X-LR married normal male
- Sons: 50% chance affected
- Daughters: 50% chance carrier
X-Linked Recessive Inheritance
- Which sex is more affected?
- Males usually only affected.
A male with mutant allele on his single x chromosome is said to be …. for that allele.
hemizygous
X-Linked Recessive Inheritance
- Transmission Between Sexes
- Transmitted through unaffected carrier females to their sons
- Males cannot transmit the disorder to their sons i.e. no male to male transmission.
- A male transmits his x chromosome to each of his daughters and his Y chromosome to each of his sons.
X-Linked Recessive Inheritance
- Examples
- Hemophilia A
- G6PD deficiency
- Muscular dystrophy
- Color blindness
Explain Sex controlled inheritance
- Some genes gives an effect in male different from that in female
Examples of Sex controlled inheritance
Tone of voice (High pitch in male and vice versa)
Explain Sex limited inheritance
Gene expresses itself in only one sex and not the other
Example of Sex limited inheritance
PLUS Y-Linked Inheritance
Gene determining a heavy beard in male
Def of Multi-Factorial Inheritance
In Multi-Factorial Inheritance
- The magnitude of the trait is determined by:
Normal traits inherited by Multifactorial Inheritance
Abnormal traits inherited by Multifactorial Inheritance
Def of Non-Traditional Inheritance
- Inheritance patterns which do not fall into the chromosomal, single gene, or multifactorial categories
Examples of Non-Traditional Inheritance
- Cytoplasmic inheritance
- Mosaicism
- Uniparental disomy
