Mendelian Inheritance Flashcards
What is a compound heterozygote?
A person who has two mutant alleles of a gene
What does hemizygous mean?
Special case in which a male has an abnormal allele for a gene located on the X chromosome and there is no other copy (no other X chromosome) so he is neither homo nor heterozygous but hemizygous
What is a single gene disorder?
One that is determined primarily by alleles at a single locus, referred to as mendelian
What is pleiotropy?
When a mutation in a single gene results in various manifefstations of disease (i.e. many different symptoms)
What are the 3 types of mendelian inheritance?
Autosomal Dominant
Autosomal Recessive
X-linked
What is penetrance?
Probability that a mutant allele or alleles will have any phenotypic expression
What is expressivity?
Refers to the severity of expression of the phenotype among individuals with the disease causing genotype
What is a proband?
A person serving as the starting point for the genetic study of a family
What is allelic heterogeneity?
Different mutations in the same gene produce the same or similar phenotype
What is locus heterogeneity?
Mutations in different genes produce the same or similar phenotypes
What factors would be potentially indicative of a single gene disorder?
- The condition is present in multiple family members
- There is an earlier age of onset than expected
- More common in monozygotic twins than dizygotic
- Collection of symptoms points to a known genetic disorder
- The disease is more common in certain ethnic groups
What are the characteristics of autosomal dominant inheritance?
- Single copy of pathogenic allele causes disease
- Allele is on autosome
- Males and females should be equally likely to be affected
- Likely to be seen in a member of every generation of a family
What are some reasons why a single copy of a pathogenic allele would be sufficient to cause disease?
- Haploinsufficiency - amount of gene product produced by remaining normal copy may not be enough for normal function
- Toxic gain of function - may result in too much gene product
- Dominant negative interference: products of abnormal allele may interfere with products of normal allele
- Two hit hypothesis - it’s possible that someone could possess a germ line mutation and then acquire a somatic mutation later in life that makes them more likely to produce disease
What are characteristics of autosomal recessive inheritance?
- Most couples who have a child with autosomal recessive disorder do not have family history of disorder
- Child inherits mutant allele from each parent
- Heterozygote typically unaffected
- Affected individuals typically restricted to one generation
- Consanguinity may be present especially if the disease is rare
- Males/females equally likely to be affected
- Allele is on autosome
What are the characteristics of X-linked RECESSIVE inheritance?
- The phenotype is expressed in all males with the mutant allele due to their being hemizygous
- Risk of disease in each son of female carrier is 1/2
- Each daughter of female carrier has 1/2 chance of being a carrier
- Male to male transmission never occurs
- All daughters of an affected male are carriers
- Female carriers do not exhibit disease
