Biochem11 Flashcards
Genetic terms
Both alleles contribute to the phenotype of the heterozygote.
Codominance
ex. Blood groups A, B, AB
Phenotype varies among individuals with same genotype.
Variable expressivity
ex. 2 patients with neurofibromatosis type I may have varying disease severity
Not all individuals with a mutant genotype show the mutant phenotype.
Incomplete penetrance
Ex. BRCA1 gene mutations do not always result in breast or ovarian cancer
One gene contributes to multiple phenotypic effects.
Pleiotropy
Ex. PKU causes many seemingly unrelated symptoms, ranging from mental retardation to hair/skin changes
Differences in gene expression depend on whether the mutation is of maternal or paternal origin.
Imprinting
Ex. Prader-WIlli & Angelmann’s syndromes
Increased severity or earlier onset of disease in succeeding generations.
Anticipation
Ex. Huntington’s DZ
If a patient inherits or develops a mutation in a tumor suppressor gene, the complemntary allele must be deleted/mutated before cancer develops. This is not true of oncogenes.
Loss of heterozygosity
Ex. Retinoblastoma and the “two-hit hypothesis”
Exerts a dominant effect. A heterozygote produces a nonfunctional altered protein that also prevents the normal gene product from functioning.
Dominant negative mutation
Ex. Mutation of a transcription factor in its allosteric site. Nonfunctioning mutant can still bind DNA, preventing wild-type transcription factor from binding
Tendency for certain alleles at 2 linked loci to occur together more often than expected by chance. Measured in a population, not in a family, and often varies in different populations.
Linkage disequilibrium
Occurs when cells in the body differ in genetic makeup due to postfertilization loss or change of genetic information during mitosis.
Mosaicism
Can be germ-line mosaic (gonadal mosaicism), which may produce disease that is not carried by parent’s somatic cells
What is a chimeric individual?
Person derived from 2 zygotes that subsequently fused
Mutations at different loci can produce the same phenotype.
Locus heterogeneity
Ex. Marfan’s syndrome, MEN 2B and homocystinuria; all cause marfanoid habitus
Albinism
Presence of both normal and mutated mtDNA, resulting in variable expression in mitochondrial inherited disease.
Heteroplasmy
Offspring recieves 2 copies of a chromosome from 1 parent and no copies from the other
Uniparental disomy
What are the Hardy-Weinberg equations if p and q are the frequencies of separate alleles?
p^2 + 2pq + q^2 = 1 and
p + q = 1
HW equation - p^2 =
frequency of homozygosity for allele p
HW equation - q^2 =
frequency of homozygosity for allele q
HW equation - 2pq =
frequency of heterozygosity (carrier frequency, if an autosomal recessive disease)
HW equation - The frequency of an X-linked recessive disease in males = ___ and in females = ___.
males = q females = q^2
Hardy-Weinberg law assumes:
No mutation occuring at the locus
No selection for any of the genotypes at the locus
Completely random mating
No net migration
Both Prader-Willi and Angelman’s syndromes are due to inactivation or deletion of genes on what chromosome?
Chr 15 - Imprinting
With 1 allele inactivated, deletion of the active allele = disease
What allele is NOT expressed in Prader-Willi syndrome?
Paternal allele (P - Prader, Paternal)
What are the findings in Prader-WIlli syndrome?
Mental retardation
Hyperphagia –> Obesity
Hypogonadism
Hypotonia
What allele is NOT expressed in Angelman’s syndrome?
Maternal allele (M - angelMan’s, Maternal)
