LaCount Lec 1 Flashcards
what are single gene disorders?
recessive, dominant, autosomal, sex-linked
what is recessive
Observed in absence of normal allele (homozygous)
what is dominant
Observed in presence of normal allele (heterozygous)
what is autosomal
chromsomes 1-22
what is sex-linked
x and y chromosomes
what are Mendelian traits
autosomal dominant, autosomal recessive, and x linked recessive
what is autosomal dominant
- 50% chance passing trait to child
–> Same probability for M/F - Unaffected relatives/siblings do not transmit disorder
- Age of onset is delayed for some
–> Huntington’s disease
–> Appear later in life for signs/symptoms
what is autosomal recessive
- If both parents have mutant gene
–> 25% = affected child
–> 50% = carrier child
–> 25% = noncarrier child
–> Same probability for M/F - Unaffected siblings may be carriers (67%)
- All children of affected parent are carriers
- Age is early in life for many conditions
- Symptoms tend to be more uniform than dominant disorders
what is x-linked recessive
- Circle with blue dot inside = carrier female
- 50% chance of passing gene to sons and daughters
–> Daughters unaffected
–> Males who receive gene are affected - Affected males
–> Do not pass to sons
–> Pass mutant gene to daughters - Only males are affected
–> Females can be affected if father has trait and has children with female (rare)
what are examples of x linked diseases
- Hemophilia A & B
- Joint bleeding, muscle hematoma, soft tissue bleeding
–> A = factor 8
–> B = factor 9 - Incidence
–> A - 1: 5000
–> B - 1: 30,000 - Mutations
–> A - inversion & small deletions
–> B - missense
what is penetrance
- Many people who have a mutation in a specific gene show any traits associated with defects in that gene
- Complete: 100%
- Incomplete: <100%
- Even if people do not have pentrance they still have the gene but just do not show it
what is expressivity
- Mutations in a gene give rise to different outcomes in different people
- Number
- Identity (types)
- Extent (severity) - Ranges from complete to minimal
what is expressivity affected by
- Other genes
- Environment
- Age
- Exposure to harmful chemicals/ conditions
what are silent mutations
Replacement of a single nucleotide that results in the same amino acid still so you cannot see if there has been a mutation because the sequence does not change
what are missense mutations
Replacement of single nucleotide
&
Incorrect amino acid, which may produce a malfunctioning protein
