Mendelian Inheritance Flashcards
A red flower and a white flower make a pink flower. This is an example of
Codominance: both alleles get expressed; heterozygote is clinically distinguishable from either homozygote
How is the ABO blood group an example of codominance?
A and B are codominant alleles –> AB phenotype
Reduced Penetrance- what does it look like on a pedigree and what is it?
Looks like the disorder has “skipped” a generation.
The person carrying the gene would show NO signs of the disorder.
Variable expressivity
The extent that the genetic disorder is clinically evident in an individual who carries the gene.
Usually in terms of severity, but the same gene may even cause a different phenotype in different family members(e.g. Schizophrenia and Bipolar disorder)
NF, Waardenburg syndrome, and Marfan are examples of
Autosomal dominant disorders with variable expressivity - the severity varies
Varying degrees of deafness, minor defects on neural crest structures, pigmentation changes
Waardenburg syndrome - autosomal dominant, variable expressivity
Tall and thin; long arms, fingers, toes
Marfan’s syndrome: an autosomal dominant disorder that affects elastic fibers –> can lead to aortic dissection
Cafe au lait spots indicates what disorder?
Neurofibromatosis (NF): autosomal dominant disordr caused by mutations in the NF gene that cause Schwann cells to grow into tumors called neurofibromas; some get much mroe severe symptoms than others (variable expressivity)
New Mutation Rate- what is it and what is it sometimes associated with?
Individuals with autosomal dominant disorders may have no affected parents and may be the first in their family with the gene
sometimes associated with advanced paternal age. I
Achondroplasia - what is it and what type of disorder is it?
Autosomal dominant disorder that prevents cartilage changing into bone –> dwarfism, limited range of motion, small fingers, macrocephaly, normal intelligence
Osteogenesis Imperfecta - what type of disorder is it?
Autosomal dominant disorder (imperfect boen formaiton)
Allelic/intralocus vs Locus/interlocus heterogeneity
Allelic/intralocus heterogeneity is when different mutations in a single gene can cause the same disorder
Locus/interlocus heterogeneity is when mutations in different genes can cause the same disorder
Albinism is what type of disorder? It demonstrates what important genetic concept?
Autosomal recessive disorder
Can be caused by different genes (tyrosine positive or tyrosine negative), so it’s an example of heterogeneity
Ethnicity of Disease
Especially for recessive diseases - more likely to carry same deleterious genes if parents are of the same ethnicity or are related.
Sickle Cell Anemia, Tay Sachs, and most inborn errors of metabolism are _______ disorders, with the exception of
Autosomal recessive, except Hunter syndrome
In autosomal recessive disorders, what do we assume about the parents of an affected child?
They’re both heterozygous carriers and are asymptomatic; may have consanguinity
UNLESS there’s uniparental disomy (2 copies of a chromosome came form the same parent)
Lyon’s hypothesis in females
Primordial cell chooses which X to shut down and all daughter cells descending from that cell shuts down the same X chromosome –> The heterozygote is really a hemizygote because some cells wille express one allele, some the other
Mosaicism
2 cell lines of different genotype are derived from the same zygote
Sex limited traits
Autosomally transmitted, but expressed in only one sex
Ex) Precocious puberty
Progressive muscle degeneration early in childhood; delays in sitting and standing in independently
Duchenne muscular dystrophy - an X-linked recessive disorder that causes alterations in the dystrophin protein that keeps muscle cells intact
Hunter’s syndrome
X-linked recessive disorder (only metabolism disorder that is NOT AR)
Lysosomal storage disease that affects GAGs –> Thickened skull, ribs, vertebral abnormalities, hepatosplenomegaly, retardation
- Trait appears in every generation - affected persons usually have an affected parent (new mutations are possible) – vertical pedigree pattern
- Recurrence risk is 50% for affected individual to produce affected offspring. Note: Male-to-male transmission can occur.
- Unaffected individuals do not transmit the disorder to their children
AD
- Disorder appears in siblings of the family – horizontal pedigree pattern
- May skip generations
- Recurrence risk is 25% that sibs of an affected individual will also be affected.
- Parents of affected individuals may be consanguineous.
AR
Both parents are obligate heterozygous carriers
- Incidence of the disorder is much higher in males.
-
Affected man gives it to all his daughters, and half his sons
- All daughters of an affected male are carriers.
- Affected males related to one another through females.
- Carrier females may show variable expression of trait - depending on X- inactivation
- FATHER TO SON DOES NOT OCCUR
X-linked recessive disorder
