Háziasítás (Zöldág
2019.09.26. UNIVERSITY OF VETERINARY MEDICINE - BUDAPEST DEPARTMENT OF ANIMAL BREEDING NUTRITION AND LABORATORY ANIMAL SCIENCE SECTION FOR ANIMAL BREEDING AND GENETICS Gene effects, Mendelian exceptions László Zöldág prof. emer. Mendel’s laws in simple inheritance (for monogenic traits!) Preconditions: monogenic, single locus, location on different chromosomes, not X-linked! 1. Homozygosity of parents • 2. Uniformity and reciprocity (criss-cross) in F1 generation: – identity of genotype and phenotype in case of homozygous parents, – independently which of parents carries the dominant or the recessive genes. • 3. Segregation in F2 generation (1:2:1, 3:1): reappearance of parental characteristics in F2 generation • 4. Independent and free segregation and new combinations of genes at diff. loci (9:3:3:1 segregation in case of two loci): inter-chromosomal or Mendelian recombination in mono-, di-, tri- and polyhybrid crossings. 1 2019.09.26. Exceptions for Mendelian Rules: Terminology • Varied expressivity of dominant genes (white spotting and grey colour in horses, epigenetics) • Incomplete penetrance of dominant genes (%, canine JKD) • Multiple alleles, allelic polymorphism (on the same locus) • Epistasis (interlocal interaction of genes, coat colours - oligogenie) – Complementary or epistatic oligogenie (comb types of fowl, coat colours) • Genetic heterogeneity (mimic genes, diff. genotypes the same phenotype) • Linkage and crossing over (intrachromosomale recombination) • Pleiotropy (dosage effect or linkage, „side” effects of genes, Polledness in goats, lethal genes, FecX in sheep) • Sex-X(Z)-linked inheritance (sexing, auto-sexing chicks, X-linked diseases) • Uniparental inheritance (genomic imprinting, maternal inheritance – mtDNA) Changes in gene effects: Mendelian inheritance is not true (?) • Expressivity of genes: – Varied manifestation of dominant genes in heterozygotes, and recessive genes in homozygotes.
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