Govt Exams
Genomic imprinting involves parent-specific gene silencing. If only the paternal mutation causes disease, it indicates the maternal allele is normally silenced (imprinted), making the paternal allele the only functional copy.
Epigenetic changes (DNA methylation, histone modifications) and differential environmental exposure can cause phenotypic differences in genetically identical individuals.
A bottleneck reduces population size dramatically, causing random loss of alleles and making genetic drift the dominant evolutionary force, reducing genetic variation.
Without crossing over, the number of different gamete types = 2^n, where n = number of heterozygous gene pairs = 2^5 = 32.
Random assortment of chromosomes during meiosis doesn't change allele frequencies; it only creates different combinations. Selection, drift, and gene flow all change frequencies.
Total individuals = 1000. p = (200+300)/2000 = 0.25, q = 0.75. Expected: BB = 62.5, Bb = 375, bb = 562.5. Observed shows excess homozygotes, indicating inbreeding or population substructure.
Interference = 1 - Coefficient of Coincidence = 1 - 0.8 = 0.2. This measures how much one crossover interferes with adjacent crossovers.
In small populations, genetic drift can cause alleles to be randomly lost. With frequency only 0.02 in a population of 100, the allele is vulnerable to random loss.
Mutations in non-coding regions vary in importance. Those in regulatory elements (promoters, enhancers) can be significant; most others are neutral.
For X-linked traits in males (hemizygous), allele frequency equals phenotype frequency. In females at equilibrium, the allele frequency is the same as in males: 0.1