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Genetics
First Aid - Biochem - Genetics
Question | Answer |
---|---|
variable expression | nature and severity of phenotype vary from 1 person to another - ex. 2 patients with neurofibromatosis may have varying dz. severity |
incomplete penetrance | not all individuals with a mutant genotype show the mutant phenotype |
pleiotropy | 1 gene has multiple effets on an individual's phenotype - ex. PKU causes many seemingly unrelated sx. ranging from mental retardation to hair and skin changes |
anticipation | severity of dz. worsens or age of onset of dz. is earlier in succeeding generations - ex. huntington's dz. |
loss of heterozygosity | pt. inherits or develops a mutation in a tumor suppressor gene, the complementary allele must be deleted/mutated before cancer develops - this is not true of oncogenes (can lose 1 and still function?) - retinoblastoma |
dominant negative mutation | exerts a dominant effect - heterozygote produces nonfunctional altered protein that also prevents the normal gene product from functioning -mutation of TF in its allosteric site, nonfunctioning mutant can still bind DNA and prevent nml TF binding |
Hardy-Weinberg Law | assumes no mutation at locus, no selection for any genotypes, completely random mating, and no migration |
Hardy-Weinberg equations | dz. prevalence = p2 + 2pq + q2 =1 allele prev. = p + q = 1 heterozygote prev. = 2pq (x linked recessive males = q/females = q2) |
Autosomal dominant disease examples | familial adenomatous polyposis, marfan's syndrome |
Autosomal recessive disease examples | PKU, sickle cell, thalassemias, CF |
X-linked recessive disorder examples | G6PD, Lesch-Nyhan |
Trinucleotide repeat expansion disease example | Fragile-X syndrome |
Autosomal trisomy disease example | Down syndrome |
Deletion syndrome examples | Cri du chat, DiGeorge (22q11) |
Familial adenomatous polyposis | colon becomes covered with polyps > colon cancer, deletion on chromosome 5 (APC gene) |
Cri du chat | congenital microdeletion of short arm of chromosome 5, microcephaly, mental retardation, high pitched crying/mewing, epicanthal folds, cardiac abnormalities |