Genetic Abnormalities Flashcards
4 types of abnormalities
- monogenic
- polygenic
- mitochrondral gene
- chromosomal
monogenic abnormalities (single gene)
- d/t defective or mutant allele at a single gene locus
- pattern of inheritance depends on whether phenotype dominant or recessive and whether gene located on an autosomal or sex Chr
- leads to formation of abn protein or dec protein production of a gene product
formation of abn proteins/dec protein production of gene product results in:
- defective enzyme/dec amount of an enzyme
- defects in receptor proteins and their Fx
- alterations in non-enzyme proteins
- mutations resulting in unusual rxns to drugs
3 types of monogenic abnormalities
- autosomal dominant disorder
- autosomal recessive disorder
- X-linked disorders or “sex linked disorders”
autosomal dominant disorder
- a single mutant allele from an affected parent is transmitted to an offspring regardless of sex
- affected parents has 50% chance of transmitting disorder to each offspring
autosomal recessive disorder
- manifested only when both members of the gene pair are affected
- both parents could be unaffected but carriers of defective gene
- heterozygous carriers to not usually produce symptoms
autosomal recessive disorder: if one parent fully affected than how many % of children are carriers?
100%
autosomal recessive disorder: if both parents are carriers of the mutant gene how many are affected, carriers, and unaffected and non-carriers?
- 25% affected
- 50% carriers
- 25% unaffected and non-carriers
X-linked disorders or “sex linked disorders”
- most sex Chr defects are on the X (fem) Chr
- males most often affected
- females = XX (if 1 Chr affected, there’s another normal X Chr to make up for it; carrier of mutation)
- males = XY (no other normal X Chr to make up for it –> mutation mnfts into disorder)
X-linked disorders: an unaffected mother carries 1 normal and 1 mutant allele on the X Chr… what are the chances of transmitting defective gene to her sons?
- 50% chance
X-linked disorders: an affected father procreates… does he transmit the defective gene to his daughters?
yes, he transmits the defective gene to all his daughters who become carriers of the mutant gene
X-linked disorders: an affected father procreates… does he transmit the defective gene to his sons?
no, b/c Y Chr genes are unaffected –> male does not transmit defect to any of his sons (sons cannot be carriers)
polygenic/complex abnormality
- caused by multiple genes (2 or more) and environ factors (ex. viral infect)
- expressed during fetal life and present @ birth; or may be expressed later in life (enviro factors)
mitochrondrial gene disorders
dysfunctional mitochondria, the organelle that produces ATP
mitochrondrial genes
- DNA not only in nucleus, but small amount also in mitochondria
- 37 mitochondrial genes
- involved in prod of ATP
- code for enzymes in electron transport chain in the mitochondria
- most mitochondrial defects mnft in neuromuscular defects
chromosomal defects abnormality
- defect in # OR structure of Chrs
- can use karyotype test
- extra or missing Chr or abn positions of Chr pieces –> cause problems w person’s growth, development and body Fx
numerical abnormality – aneuploidy (Chr)
problem r/t # of Chr (more or less than usual)
numerical abnormality – monosomy (Chr)
1 Chr pair lacking a Chr (1 missing Chr)
- usually lethal, unless it occurs in sex Chr
numerical abnormality – trisomy (Chr)
extra Chr in a pair
- named by Chr pair affected
- Ex. Down Syndrome = Trisomy 21
Turner’s syndrome
- female has missing X Chr (monosomy)
- 1 in 2500 births
- instead of XX, gametes written as XO
- autosomal Chr vital to cellular Fx and sustaining life, but sex Chr are not necessary for survival
- — there fore, someone can live with Turner’s syndrome, but may have issues w reproduction
Klinefelter’s syndrome
- male has extra X Chr (trisomy)
- XXY – pt has 47 Chr
structural defects (Chr)
- under certain circumstances, a section of a Chr can break off
structural defects – deletion (Chr)
lose a piece of a Chr (one in pair)
- detached segment does not reattach to the original Chr
- leads to loss of genetic material and shortening of the Chr
structural defects – inversion (Chr)
piece of Chr inverts (top –> bottom)
- reverses its orientation and reattaches to the original Chr
- 2 breaks in a single Chr (pericentric = around the centromere; paracentric = away from the centromere)
- the entire Chr does not invert, but a portion of the Chr
structural defects – translocation (Chr)
piece transferred over to other Chr
- segment breaks off and attaches to non-homologous Chr
balanced translocation
2 nonhomologous Chrs exchange the same segment of DNA
Robertsoninan Translocation
2 nonhomologous acrocentric (centromere close to one end) Chr break near their centromeres and then fuses to form one large metacentric (centromere in the middle) Chr
isochromosomal translocation
faulty centromere division, leads to duplication of long arm and deletion of short arm, or the reverse (divide horizontally across centromere instead of vertically)
