Autosomal Inheritance Flashcards
Which chromosomes are autosomes? What inheritance pattern do autosomes show?
Autosomes are chromosomes 1-22, and provide the majority of genetic information. They show mendelian inheritance, in which the sex of the parent and offspring has no effect.
How common are autosomal dominant disorders?
1/200 people have an autosomal dominant disorder
What are some clues that indicate autosomal dominant inheritance?
- There are affected individuals in every generation
- Both sexes are equally affected
- Father-son transmission is possible (rules out x linked)
- Half of children will be affected, and at least one parent (rare for affected people to mate)
Name 3 autosomal dominant disorders.
- Retinoblastoma - tumors form in retina and can fill the eye (white pupil)
- Postaxial polydactyly - extra toes
- Achondroplasia - little people
What are some clues indicative of autosomal recessive disorders?
Result of two carriers mating
- result in 1/4 normal, 1/2 carriers, and 1/4 affected
- risk is 25% for every child
- may not be in every generation - “skips a generation”
- Consanguinuity is a risk factor
Name two autosomal recessive disorders.
- Albinism - inability to produce melanin from tyrosine
- Cystic Fibrosis - disruption of chloride transport
Describe Cystic Fibrosis.
A recessive disorder, more common in European ancestry.
Disrupts chloride transport - excess chloride in sweat
pancreatic secretions affected due to clogging, enzymes don’t reach intestine, resulting in malnutrition, and mucousy malodorous stool
thickened secretions in lungs, unable to clear debris
Describe how dominant and recessive inheritance is not rigid.
How can severity of disease change with genotype?
How can some disorders be due to dominant and recessive disorders?
Dominant and recessive inheritance does vary, and is not as rigid as a structure we put it in order to understand.
Homozygotes for a dominant disorder are often more severely effected.
Disorders source can vary due to different genes in the same pathway, or different molecular interactions of a mutant with proteins. Phenotype is more important for categorizing disease than genotype.
When should a new mutation be considered?
- Inheritance pattern shows no other effected individuals where this would be likely.
- Parentage has been confirmed
- Neither parent has evidence of carrying the mutation
Describe germline mosaicism.
When a mutation occurs in an embryonic cell this is passed to all daughter cells, but not all cells of the organism. This results in an organism that is a mosaic of mutated and non-mutated cells.
What are three ways a mutation may go unnoticed in an affected individual?
- Delayed age of onset - disorders not evident until adulthood, after children
- Reduced penetrance - phenotype is mild or not present due to modifying genes, may be more obvious in children
- Age-dependent penetrance - combination of delayed age of onset and reduced penetrance
Describe neurofibromatosis. What is its inheritance? What characteristic is this disorder a great example of?
Skin lesions called “cafe au lait” spots.
Autosomal dominant disorder with variable expression - some get few/mild skin lesions others grow very large tumors
Define pleiotropy. What are the two major categories of genes?
Pleiotropy is the act of one mutation resulting in multiple effects or a single gene affecting multiple tissues.
Two categories of genes:
- DNA transcription factors
- Extracellular matrix proteins
Describe Marfan Syndrome. What effect is this an example of?
Tall, thin, long extremities. Arachnodactyly. Vessel problems. Special glasses.
Example of pleiotropy, as one gene causes several effects.
Describe allelic heterogeneity. What are some examples of this?
When there are multiple mutant forms that cause different effects with mutations of the same gene.
Ex: hemoglobin disorders such as sickle cell and beta-thalassemia
