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list three types of mutations
- 1. point mutation
- 2. frameshift mutation
- 3. trinucleotide repeat mutation
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what are mendelian disorders?
single-gene defects
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what is an example of a point mutation disease?
sickle cell
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what is an example of a trinucleotide repeat mutation?
fragile x syndrome
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describe an autosomal dominant disorder
the disease will be clinically evident with only one copy of the gene at a given locus. it usually creates outward physical changes and a delayed age of onset.
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give an example of an autosomal dominant disease
huntington disease
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how many of the offspring will inherit this disease if only one parent is affected?
50%
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define reduced/incomplete penetrance
a person has the mutant gene but fails to express it
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define de novo mutation
disease arising from a new mutation who do not have affected parents.
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describe an autosomal recessive disorder
trait is expressed only if both genes at a given locus are affected (homozygous individuals)
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how many offspring of a heterozygotic parents would inherit an autosomal recessive disorder?
25%, 50% become carriers
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what type of problems do autosomal recessive disorders cause?
enzyme defects that produce errors in metabolism. heterozygotes maybe not present clinically but may have reduced levels of normal enzymes. onset of age is usually early in life. they are also more expressed uniform and complete penetrance is common.
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describe X-linked disorders
transmitted on sex chromosomes and can be dominant or recessive (sex-linked). no Y-linked diseases are known, although hairy ears maybe be carried on the Y
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describe X-linked recessive diseases
almost all x-linked disorders are recessive. females are carriers if heterozygous; homozygous females and hemizygous males are affected (all males affected)
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describe lyonization
sixteen days after conception, all but one X chromosome is randomly inactivated in al of the cells within the zygote.
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describe unfavorable lyonization
inactivation of an abnormally high percentage of normal X chromosomes, leading to clinical evidence of the disease in a heterozygote.
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what type of disorder is marfan syndrome?
mutation in structure proteins
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list 2 diseases caused by mutations in structural proteins
marfan syndrome and Ehlers-Danlos syndrome
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describe marfan syndrome
autosomal dominant disorder affecting the CT due to mutation of the FBN1 gene causing production of abnormal fibrillin. fibrillin is important in the production of fibrillin is essential to elastic fiber production. this causes a tall, thin body, arachnodactyly, dislocation of the lens of the eye, and aortic aneurysm.
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describe ehlers-danlos syndrome
causes a problem with collagen synthesis. results in hyperextensible skin and hypermobile joints. fragile skin and delayed wound healing. hernias are common.
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give an example of a disease caused by mutations in receptor proteins
familial hypercholesterolemia
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describe familial hypercholesterolemia
mutation in gene for LDL receptor results in impaired metabolism and increased LDL cholesterol in plasma. can cause xanthomas and premature atherosclerosis. heterozygotes have 2-3x increased LDL levels, homozygotes have 5x normal levels. homozygotes often die by 15 yo.
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familial hypercholesterolemia can be controlled with what type of drug?
statins
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list 2 diseases caused by mutations in enzyme proteins
phenylketonuria (PKU) and lysosomal storage disease
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describe PKU
autosomal recessive disorder causing severe lack of phenylalanine hydroxylase. affected indiv. are normal at birth but elevated phenylalanine levels impair brain development and retardation by 6 months. restriction of dietary phenylalanine intake will prevent retardation.
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describe lysosomal storage disease
autosomal recessive affecting infants and young children. causes an accumulation of insoluble large molecules in macrophages leading to hepatosplenomegaly. can cause retardation/early death.
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give 4 examples of lysosomal storage diseases
- 1. tay-sachs
- 2. neimann-pick
- 3. gaucher
- 4. mucopolysaccharidoses
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what is the normal chromosome count? how many pairs of autosomes and how many pairs of sex chromosomes?
46, 22, 1
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define polyploidy
increased chromosome count that is a multiple of a normally seen number (4x23).
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define euploid
having 46 chromosomes
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define aneuploidy
any number that is not an exact multiple of the normal chromosome count, like having an extra chromosome in trisomy 21 (47 chromosomes)
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describe 3 structural abnoromalities
- translocation: transfer of a part of one chromosome to another nonhomologous chromosome
- deletion: loss of a portion of a chromosome
- inversion: when a chromosome breaks into 2 points and released fragment is reunited after a 180 turn.
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list 2 cytogenetic disorders involving sex chromosomes
klinefelter syndrome and turner syndrome
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describe klinefelter syndrome
XXY males with hypogonadism. increased length of lower limbs, reduced body hair and gynecomastia. increased frequency of taurodontism.
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describe turner syndrome
monosomy with only X chromosome. short stature, webbed neck, low posterior hairline. high-arched palate. cardiovascular malformations; failure to develop secondary sex characteristics, primary amenorrhea
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what are the indications for prenatal genetic analysis
- 1. mother's age >34 yo
- 2. parent is a carrier of a chromosomal translocation
- 3. history of a previous child with chromosomal abnormality
- 4. parent is a carrier of an x-linked disorder
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what are the indications for postnatal genetic analysis?
- 1. congenital abnormalities
- 2. unexplained retardation and/or developmental delay
- 3. suspected aneuploidy
- 4. suspected sex chromosomal abnormalit
- 5. infertility
- 6. multiple spontaneous abortions
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