Terms/Definitions Flashcards
(32 cards)
Codominance
Definition + example
Both alleles contribute to phenotype of heterozygote
ex. AB blood type
- alpha-1-antitrypsin deficiency
Variable expressivity
Pt. w/ same genotype, but varying phenotype
Ex. 2 patients with neurofibromatosis type 1 (NF1) can have varying disease severity
Incomplete penetrance
Not all individuals with mutant genotype show the mutant phenotype
ex. BRCA1 mutation; doesn’t always cause breast or ovarian cancer
Pleiotropy
One gene contributes to multiple phenotypic effects
ex. untreated PKU –> light skin, intellectual disability, musty body odour
ex. sickle cell disease
ex. cystic fibrosis
Anticipation
Increased severity of earlier onset of disease in succeeding generations
ex. Huntingtons, trinucleotide repeat diseases
Loss of heterozygosity
Loss of a normal allele from region of one chromosome of a pair that allows a defective allele on the homologous chromosome to be clinically manifested
- -> Pt. may inherit/develop mutation in tumor suppressor gene (TSG), but the remaining allele is still functioning on the other gene of the chromosome pair. But if there is a loss of heterozygosity with the “normal” allele, normal function is lost (i.e. no TSG) and can lead to development of cancer.
ex. retinoblastoma, lynch syndrome (HNPCC), Li-Fraumeni syndrome, breast cancer
Mosaicism
Presence of genetically distinct cell lines in same individual
ex. McCune-Albright syndrome
Locus heterogeneity
Mutations at different loci can produce similar phenotype
ex. albinism, waardenburg syndrome , deafness, retinitis pigmentosa
Allelic heterogeneity
Different mutations in same locus produce same phenotype
ex. beta-thalassemia, achondroplasia, familial hypercholesterolemia, polydadctyly
Heteroplasmy
Presence of more than one kind of mitochondrial DNA in mitochondria of a single individual
What is the Hardy-Weinberg law?
Law assumptions about population:
- no mutation occurs at locus
- natural selection is not occurring
- completely random mating
- no net migration
What is uniparental disomy? (UDP)
Offspring receive 2 copies of a chromosome from one parent and NO copies from other parent.
HeterodIsomy (heterozyg) –> indicates meiosis I problem
Isodisomy (Homozyg) –> indicates meiosis II error or post zygotic chromosomal duplication and loss of original
** They still have correct # of chromosomes; euploid (NOT aneuploid!)
- usually normal phenotype
Imprinting
Phenomenon of different expression of alleles depending on parent of origin.
At some loci, only one allele is active. The other is inactive (via imprinting/inactivation by methylation)
- if the functioning allele is deleted, it will cause a disease
ex. - Angelman syndrome
- Prader-Willi syndrome
(both chromosome 15 deletion/mutation)
Describe type of genetic problem and which type for these syndromes:
- Prader-Willi syndrome
- Angelman syndrome
Prader-willi syndrome –> MATERNAL imprinting. Maternal gene is silent, the paternal gene is deleted/mutated.
Angelman syndrome –> PATERNAL imprinting. Paternal gene is silent, maternal gene silent, paternal gene is mutated/deleted.
Haplotype
Set/cluster of alleles at a loci, DNA variations or polymorphisms, that tend to be inherited together as
Linkage disequilibrium
Restriction in diversity of haplotypes causing them to be rare in population
–> 2 alleles are said to be in linkage diseq. if they inherit together more (or less) frequently than what is expected
Odds ratio
Comparison of the odds of individuals who shared a particular factor (i.e. genotype) that will express the disease/trait vs the odds of individuals without the factor
Lyonization
Phenomenon of X inactivation
Polyploidy
Any multiple of the haploid chromosome number that is other than the diploid number i.e. 3n, 4n etc. thus you have increase in complete extra set of chromosomes
Hemizygous
When one copy is present of a chromosome
ex. sex-linked traits for males are hemizygous
Haploinsufficiency
Inability to carry out a function due to only one (half) copy being present instead of two.
–> Can happen if there has been a deletion
What are homologous chromosomes?
They are chromosomes that contain DNA that code for the same gene
- BUT, homologous chromosomes are NOT replicas of each other (sister chromatids are exact replicas)
Multiple allelism
for many traits/diseases there are more than one mutant alleles @ locus (e.g. cystic fibrosis)
Ex. PKU, marfan syndrome, hemophilia A
Genetic compound
individual who has 2 mutant alleles @ locus (complex heterozygosity)
