Genetics Flashcards
Congenital Disesae
A disease that is present from birth
Hemizygotic
Has 1 allele instead of the usual 2 (e.g. sex chromosomes in males)
Polymorphism
The existence of multiple alleles for a particular gene
How many combinations of chromosomes will meiosis generate for X chromosomes?
2^X
What is a metacentric chromosome?
The centromere is located in the center of the chromosome
What is a submetacentric chromosome?
The centromere is closer to one of the ends.
What is an acrocentric chromosome?
The centromere is close to the telomere.
Aneuploidy
The loss of gain of one or more chromosomes; at least one set of chromosomes is incomplete; caused by nondisjunction
Polyploidy
More than two complete sets of chromosomes
Euploid
Containing the exact multiple of the number of chromosomes in a normal gamete (1=haploid, 2=diploid)
Partial Monosomy
Only a portion of the chromosome has one copy
Mosaicism
The presence of at least two cell lines with different genotype in an individual
Balanced chromosome arrangement
No loss or gain of essential chromosomal material
Unbalanced chromosome arrangement
Loss or gain of essential chromosomal material
Types of chromosomal structural abnormalities
Translocations (e.g. Robertsonian - fusion at the centromere of two acrocentric chromosomes like 14 and 21)
Inversions (pericentric vs. paracentric)
Isochromosome (caused by double-stranded break near centromere)
Insertions
Deletions
Duplications
Compound heterozygote
Two different alleles may cause disease
Autosomal Recessive Diseases
Gene often encodes an enzyme: Sickle cell anemia Cystic fibrosis Tay-Sachs disease Phenylketonuria Bloom’s syndrome α- and β-Thalassemia
What kinds of molecular disorders are typically dominant?
Gene products encode receptors, something in a pathway, etc. Haploinsufficiency (e.g. receptors) Dominant negative (mutant protein interferes with normal protein) New or enhanced property of the protein (e.g. overproduction of a receptor, toxic protein)
Name some X-linked recessive diseases?
Duchenne muscular dystrophy Hemophilia (A and B) Red-green color blindness Nephrogenic diabetes insipidus
Name some autosomal dominant diseases?
Familial hypercholesterolemia Osteogenesis imperfecta type II Achondroplasia (short-limed dwarfism) Huntington disease Glucose-6-phosphate dehydrogenase deficiency
Name some X-linked dominant diseases?
Fragile X syndrome (both sexes) Vitamin D resistant rickets (both sexes) Aicardi syndrome (lethal in males) Incontinentia pigmenti (lethal in males) Rett syndrome (lethal in males)
Alellic Heterogeneity
Different mutations in the same gene
Locus (Genetic) Heterogeneity
The same condition can be caused by mutations in different genes
Incomplete Penetrance
The likelihood that the disease allele will result in the disease (all or nothing)
Pleiotropy
Diverse effects of a single gene on several organs; often shows variable expression
Expressivity/Variable Expression
The degree of clinical manifestation of the same mutant allele in different individuals
Anticipation
Increasing severity of disease in successive generations (earlier onset, worsening of symptoms); often due to unstable repeat expansion.
Examples include Huntington Disease, Fragile X Syndrome, Myotonic Dystrophy, and Friedreich ataxia
Heteroplasmy
The presence of more than one type of mitochondrial DNA
Uniparental disomy
Both copies of a chromosome are received from the same parent; can cause problems with imprinting
Polygenic
Caused by the combined actions of two or more genes; proportional to the degree of relatedness
Multifactorial
Caused by the combined actions of two or more genes and environmental factors; proportional to the degree of relatedness
Concordance
The presence of a given trait in both members of a pair of twins; should be 100% if disease is purely genetic; higher concordance in MZ vs DZ twins is evidence of strong genetic component
Name some mitochondrial diseases?
Mitochondrial disorders are inherited exclusively from mothers
- Leber hereditary optic neuropathy: bilateral blindness
- Myoclonic epilepsy with ragged red fibers: myoclonic seizures, myopathy associated with exercise, irregularly shaped (ragged red) muscle fibers
- Mitochondrial encephalomyopathy with lactic acidosis:
