Mendelian & Population Genetics Flashcards
What are Mendel’s Laws of Inheritance?
Law of Segregation: Alleles segregate into gametes in meiosis; Law of Independent Assortment: The segregation of each pair of alleles is independent
What do penetrance, expressivity, and pleiotropy mean?
Penetrance: The fraction of individuals with a trait (disease) genotype who show manifestations of the diseaseExpressivity: The degree to which a trait is expressed in an individual (~severity).Pleiotropy: Multiple phenotypic effects of a single allele or pair of alleles Different than variable expressivity.
How are inheritance patterns in single gene disorders determined bya. quality of phenotype (dominant vs recessive)b. location of gene locus (autosomal versus sex chromosome)?
a. Recessive: horizontal on pedigree, Dominant: vertical on pedigreeb. On autosome: To be recessive one needs 2 copies of mutated allele to show phenotypic effects. To be dominant one only needs a single mutant allele to show phenotypic effects.On sex chromosome: Same rules apply but males only have one X. Thus, if a male gets a mutated X gene, since they don’t have another X to cover for the mutation - phenotypic effects of the mutation are expressed. The gene is still considered recessive because a female would need two copies to show phenotypic effects.
Please define population genetics
Population genetics: the study of allele frequencies and changes in allele frequencies in populations
What is the Hardy Weinberg formula?Do you know how to use it?
Hardy Weinberg: (alleles) p + q = 1 = p2 + 2pq + q2(genotypes)p=frequency of common allele, q=rare alleleYou should!
What are the assumptions for Hardy Weinberg?
Population is large and matings are random Allele frequencies remain constant over time because:No appreciable rate of mutationAll genotypes are equally fit (equal chance to pass alleles to next generation)No significant immigration/emigration of individuals with different allele frequencies
What is the mutation rate?
Mutation rate (μ): Frequency of new mutations at a given genetic locus; expressed as mutations/generation
How do you calculate mutation rates for autosomal dominant mutations?
Direct Method: Fully Penetrant (no hidden mutations), count the cases with no family history (the new mutations) Indirect Methods: If f=0, then all cases represent new mutations then use incidence (I) of disease to calculate μ: I=2 μ ORμ=I/2, since each of us inherits 2 allelesf = reproductive fitness
What are some other ways to estimate mutation rates?
If f!=0 then can estimate µ using various equationsAutosomal dominant: µ = 1/2 F(1-f)Autosomal recessive: µ = F(1-f)X linked recessive: µ=1/3 F (1-f)µ = mutation rate, F = frequency of disease, f = reproductive fitness
What is fitness?
Fitness (f): the probability of transmitting one’s genes to the next generationf=1 (same as normal population)f=0 (gene(s) not passed on)
Describe the events in meiosis that produce genetic variability among offspring.
Crossing over. Assortment of alleles. Reduction in genetic material from diploid to haploid.
Compare and contrast mitotic and meiotic cell divisions.
Two key differences between mitosis and meiosis are thatPaternally and maternally derived homologous chromosomes pair and crossover at the onset of meiosis (prophase I)Production of gametes versus daughter cells.
What is nondisjunction?
the missegregation of chromosomes at metaphase in either mitosis or meiosis, such that daughter cells receive extra or fewer than the normal number of chromosomes.
How is nondisjunction related to crossing over?
- Nondisjunction events are related to the positioning of chiasmata; crossover events that occur too near or too far from the centromere increase chromosome nondisjunction. Centromere-distal exchanges are less effective in ensuring appropriate spindle attachment and separation of paired homologs in meiosis I; centromere-proximal or excessive numbers of exchanges lead to entanglement of paired homologs in MI that then undergo reductional division leading to what appears to be MII errors.2. Nondisjunction events are also related to the frequency of crossover events. The reduction or absence of recombination events increases the likelihood of nondisjunction.
What are the potential effects of consanguinity?
Consanguinity is arbitrarily defined as union of individuals related to each other as close to or closer than second cousins.Likely effects: autosomal recessive disorder that has been dormant for many generations may show up in children.
