Lecture 9: Clinical Genetics Flashcards
What is a locus?
Position of a gene on a chromosome.
What is an allele?
A series of 2+ genes occupying same location of a chromosome.
What are the mendelian patterns of inheritance?
Autosomal dominant
Autosomal recessive
Sex-linked
What is XY and XX? What does it mean phenotypically? What is important about the Y?
X is inherently female.
Y is what gives male characteristics, so lack of Y = female.
XX is phenotypically female
XY is phenotypically male
Which sex chromosome is bigger?
X
Where do males get their X from?
Mother only
What is the key characteristic of an autosomal dominant disorder?
An affected person usually has at least one affected parent.
What are 2 examples an autosomal dominant disorder?
Huntington’s Disease: degenerative nerve disease from mutation in HTT gene
Marfan syndrome: degenerative connective tissue from mutation in FBN1 gene (prevents elastic fibers forming around connective tissue)
What is the key characteristic of an autosomal recessive disorder?
Males and females are equally affected.
What are 2 examples of an autosomal recessive disorder?
Cystic Fibrosis: mutation of CFTR, dysregulation of salts inc mucous
Sickle Cell: mutation of HBB gene, mutation in hemoglobin misshapen RBC
What are the key characteristic of an X-linked recessive disorder?
Usually affects males and all daughters of an affected male are carriers.
Females are affected only if father is affected and mother is at least a carrier.
What are 2 examples of X-linked recessive disorders?
color blindness, hemophilia
What are the key characteristics of an X-linked dominant disorder?
Very rare
Similar pedigree to autosomal dominant BUT no male to male transmission.
Note: This is because males can’t contribute an X. They only give a Y to a male.
What is an example of an X-linked dominant disorder?
rett syndrome: mutation in MECP2- early neurodevelopment disorder
What are the key characteristics of a Y-linked disorder?
ONLY MALE TO MALE
What is an example of a Y-linked disorder?
hypertrichosis
What are the key characteristics of a mitochondrial disorder?
Can affect both sexes, but only an affected mother can transmit it.
What is a disorder with mitochondrial DNA?
Leber’s Hereditary optic neuropathy: sudden vision loss around age 20, lack of mitochondria leads to cell death
(myopathy or neurological problems)
What is a polygenic trait?
A trait involving multiple alleles at different loci that affect a phenotype.
What is multifactorial inheritance?
Interaction between genes and environment.
What is penetrance for genetics?
% of individual with a given genotype that exhibit the phenotype.
What is nonpenetrance?
Failure of a phenotype to manifest even with a given genotype. (makes risk assessment hard since phenotype can skip a generation)
What is expressivity?
The extent to which a given genotype is expressed at the phenotypic level.
Note: You can have variable expressivity in the same family.
What causes expressivity?
Modifier genes
