Mendelian Genetics Flashcards
What is Mendel’s First Law?
The Law of Segregation
At meiosis, alleles separate from each other such that each gamete receives one copy from each allele pair
What is Mendel’s Second Law?
The Law of Independent Assortment*
(At meiosis, the segregation of each pair of alleles is independent)
*genes physically near each other on the same chromosome violate this law
What is mitochondrial inheritance?
A form of non-Mendelian inheritance, where recognizable patterns can be found. The inheritance pattern is matrilineal.
Explain the difference between penetrance and expressivity.
Penetrance = the percent of individuals with a disease genotype who actually show manifestations of the disease
Expressivty = the degree to which a trait is expressed in an individual (severity); explained by sex influence, environmental factors, stochastic effects, and modifier genes
What is pleiotropy?
A term to describe multiple, different phenotypic effects due to mutation(s) in a single gene.
Often used, when phenotypes are seemingly unrelated and/or in multiple tissues
How are inheritance patterns in a single-gene disorders determined?
- Quality of the phenotype (dominant v recessive)
2. Location of gene locus (autosome v sex chromosome)
Define population genetics.
The study of allele frequencies and changes in allele frequencies in ‘populations’
What is the Hardy Weinberg principle and when is it used?
p+q =1 where p=frequency of common allele; q=rare allele
Used to estimate carrier frequencies for autosomal recessive disorders.
What is the necessary assumption of the Hardy Weinberg principle?
Populations are large and matings are random.
Why do allele frequencies remain constant over time?
● No appreciable rate of mutation
● All genotypes are equally fit (equal chance to pass alleles to next generation)
● No significant immigration/emigration of individuals with different allele frequencies
What is mutation rate?
The frequency of new mutations at a given gene locus; expressed as mutations/generation
What are the factors that affect expressivity of the phenotype in single-gene disorders?
◦ Modifier genes: genetic factors outside a trait’s genetic locus that influence that trait’s phenotype
◦ Stochastic events: The “we have no idea” category
◦ Phenocopies: Diseases due to non-genetic (environmental) factors.
What is polymorphism?
Any common genetic variant of an allele that occurs in greater than or equal to 1% of the population.
When is p + q = 1 = p^2 + 2pq + q^2 used?
When trying to determine the frequency of homo- and heterozygous phenotypes in a population
When should new mutations be considered in a patient?
When a patient develops an autosomal recessive disease.
That patient either inherited a mutant allele from each parent or inherited one mutant allele and one wild type.
Then it could have mutated de novo => recessive disease.
