What is variable expressivity?
Phenotype that varies among individuals with the same genotype (p.82)
Name a classic example of a syndrome that exhibits variable expressivity.
Neurofibromatosis type I (NF1) (p.82)
What is incomplete penetrance?
When not all individuals with a mutant genotype show the mutant phenotype (p.82)
Name an example of a genetic mutation that exhibits incomplete penetrance.
BRCA1 gene mutations do not always result in breast or ovarian cancer (p.82)
What is pleotropy?
When one gene contributes to multiple phenotypic effects (p.82)
Name an example of a pleotropic condition.
PKU causes many seemingly unrelated symptoms ranging from mental retardation to hair/ skin changes (p.82)
What is loss of heterozygosity?
When a patient inherits or develops a mutation in a tumor supressor gene, the complementary allele must be deleted/ mutated before cancer develops. This is not true of oncogenes (p.82)
Name a condition that commonly results from loss of heterozygosity?
Retinoblastoma; "two hit hypothesis" (p.82)
What is a dominant negative mutation?
A mutation that exerts a dominant effect. A heterozygote produces a nonfunctional altered protein that also prevents the normal gene product from functioning (p.82)
Give an example of the process of a dominant negative mutation.
Mutation of a transcription factor in its allosteric site. The nonfunctioning mutatnt can still bind DNA, preventing wild-type transcription factor from binding (p.82)
What is linkage disequilibrium?
The tendency of certain alleles at two linked loci to occur together more often than expected by chance. Measured in a population, not in a family and often varies across populations (p.82)
What is mosaicism?
Occurs when cells in the body differ in genetic makeup due to postfertilization loss or change of genetic information during mitosis. It can refer to a germ-line mosaic condition (gondal mosaicism) where a disease is produced that is not carried by the parent's somatic cells (p.82)
How does a chimeric individual get his genetic makeup?
From 2 zygotes that subsequently fuse (p.82)
What is locus heterogeneity? Give one example.
Mutations at different loci that produce the same phenotype (ex.) albinism (p.82)
Name three conditions that exhibit locus heterogeneity and contribute to a marfanoid habitus.
1.) Marfan's syndrome; 2.) MEN 2B; 3.) Homocystinuria (p.82)
What is heteroplasmy?
The presence of both normal and mutated mtDNA resulting in variable expression in mitochondrial inherited disease (p.82)
What is uniparental disomy?
When an offspring receives 2 copies of a chromosome from 1 parent and 0 copies from the other parent (p.83)
What type of meiosis error is indicated by heterodisomy (heterozygous)?
Meiosis I error (p.83)
What type of meiosis error is indicated by isodisomy (homozygous)?
Meiosis II error or postzygotic chromosomal duplication of one pair of chromosomes and loss of the other of the original pair (p. 83)
Are conditions of uniparental disomy euploid (correct number of chromosomes) or aneuploid?
Describe the phenotype associated with uniparental disomy.
Normal phenotype, however consider UPD in an individual manifesting a recessive disorder when only one parent is a carrier (p.83)
Describe the tenents of the Hardy Weinberg Principle.
If a population is in Hardy Weinberg Equilibrium and p and q are the frequencies of separate alleles, then p^2 + 2pq + q^2 =1 and p + q =1 (p.83)
What is the frequency of X-linked recessive disorders in males and females according to Hardy Weinberg logic?
Males = q; Females = q^2.
Name the four assumptions of the Hardy Weinberg law.
1.) no mutation occurs at the locus; 2.) no selection for any of the genotypes at the locus; 3.) completely random mating; 3.) no net migration (p.83)
What are two potential causes of genetic inactivation/ deletion?
1.) uniparental disomy; 2.) genetic imprinting (p.83)