HRR: mendelian gentics Flashcards
Describe Mendel’s 1st law
Law of segregation (1st law): Hereditary traits are determined by discrete factors (genes) that occur in pairs and segregate (separate) during transmission to
offspring. Segregation is random.
describe mendel’s second law
Traits at different genetic loci assort independently (ex: height is independent from eye color
describe the exception to mendel’s second law
An exception is if two traits are physically linked to each other on the same chromosome
Specify the genotype and phenotype ratios for the F1 & F2 generations of
homozygous dominant and homozygous recessive parents.
describe autosomal dominant inheritance
only copy of a mutation is sufficient to cause a disease; seen on a pedigree as impacting multiple generations and in both sexes. Children with a parent with an autosomal dominant mutation has a 50% chance of inheritance
name an example of an autosomal dominant condition
Huntington’s; progressive loss of motor control, cognitive and psychiatric problems. Considered 100% penetrant. Death usually occurs within 15 years, and age of onset is typically 30-45.
describe autosomal recessive inheritance
two copies of a mutation are required to cause disease; typically, the parents are healthy carriers. If both parents are carriers, the offspring have a 25% risk. Equally transmitted by men and women. Carrier screening can allow people to determine what conditions they may be carriers for.
name an example of autosomal recessive inheritance
Tay-Sachs is more common is Ashkenazi jewish ancestry, French-canadians, cajuns, PA amish. Causes progressive neurodegeneration, seizures, blindness, spasticity. Onset around 3-6 months, typically with death before age 4
describe x linked dominant inheritance
impacts both males and females, but males have the potential to have more severe impacts. There are no carriers; if you have the mutation, you have the condition. If a father is affected, the daughter has a 100% risk, where the son has a 0% risk. Daughters get their father’s X, and son’s get their fathers Y. women have a 50% risk of passing to the child regardless of gender.
describe x linked recessive inheritance
genes are on the x chromosome; females typically need two copies to be affected, as the non-mutated X can “mask” the effects of the mutated X. men will express the condition as they have one X chromosome
give an example of x linked recessive inheritance
Duchenne muscular dystrophy causes progressive muscle degeneration and weakness. Typically, has affected males and unaffected females. 1/3 of cases are due to new mutations, not inherited ones. Female carriers have an increased risk for cardiomyopathy
describe co dominant inheritance
two alleles impact the phenotype equally. Ex is ABO blood type. A and B are co dominant to O.
give an example of co dominant inheritance
alpha-1 antitrypsin deficiency is a single gene risk for lung and liver disease. With normal being M and Z being mutated, MZ causes a mildly reduced AAT, providing some increased risks for lung and liver disease. ZZ would cause severe AAT deficiency and cause high risks for lung and liver disease.
describe reduced penetrance
penetrance is the probability a genotype will express the phenotype. In reduced penetrance, some with the disease genotype have no phenotypic manifestations.
describe variable expressivity
When the type or severity of manifestations differs in individuals with the same genotype. Ex: NF1 can cause café au lait spots, learning disabilities, and brain tumors/optic nerve gliomas
describe pleiotropy
a single genetic mutation. Impacts multiple organ systems. Ex: marfans, cystic fibrosis, alport syndrome
describe heterogenity
Mutations in multiple unrelated genes cause the same or similar phenotype. Ex: BRCA ½ both cause predisposition to breast and ovarian cancer
define consanguinity
When two people are related, it increases the risk for the inheritance of recessive trait, as they’re more likely to both be unimpacted carriers. This should be considered when the inherited disorder is quite rare.
define pseudodominance
When an autosomal recessive disease is seen in multiple generations
when do we use pedigree vs population data?
We use pedigree to find carrier risk when there is a positive family history. To find carrier risk with no family history, we would use population genetics rules such as HWE
person A has a sibling with an autosomal recessive disease, but they themselves do not have it. what is their risk of passing on the condition?
2/3
what is genetics drift?
random fluctuation of frequencies in small populations
