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2 주차 수업자료. Chapter 2. Basic Genetics. Mendel: father of classic genetics. Mendelian characters Distinct Definitive Yes or no. Allele. An alternative form of gene Locus on chromosome Homozygous Same genes at the locus Heterozygous Different genes at the locus.
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Mendel: father of classic genetics • Mendelian characters • Distinct • Definitive • Yes or no
Allele • An alternative form of gene • Locus on chromosome • Homozygous • Same genes at the locus • Heterozygous • Different genes at the locus
One gene-one enzyme theory • Enzymes can have multi-subunits • Not true any more • One gene-one enzyme One gene-one protein
Wild type vs. mutant • Wild type: • Typical • Common • Adapted • Normal (not always true) • Mutant: • Genetically altered • Null: • No protein
Genotype and phenotype • Genotype phenotype • Epistasis • Interaction between genes to control a single phenotype • One gene suppresses the expression of another • Mutation in one gene masks the effect of mutation in another gene
Genes and chromosomes (1) • Homologous chromosomes • Duplicate genes
Genes and chromosomes (2) • Chromosome number: n • Haploid (e.g., bacteria): n=1 x 1 copy = 1 • Diploid (e.g., human): n=23 x 2 copies = 46 • Polyploid (e.g., wheat): n=7 x 2, 4, 6 copies = 14, 28, 42 • Aneuploid: abnormal number of chromosomes • Down syndrome (Trisomy)
Dominant and recessive alleles • Dominant • Recessive • Homozygous • Heterozygous
Partial- or co-dominant alleles • Partial dominant • (e.g., r0.5 vs. R) • Co-dominant • (e.g., R and B vs. r)
Penetrance: phenotypic effect • Variable penetrance: due to modifier genes (e.g., epistatic interaction)
Germ cells: progenitor of gametes • Germ cells vs. somatic cells • Meiosis vs. mitosis
Genotype determination (1) • F0 F1 • Homozygous dominant X • Homozygous recessive • Offspring (progeny): All heterozygous
Genotype determination (2) • F1 F2 • Heterozygous X • Heterozygous • Offspring (progeny): Mendelian ratio, 1:2:1 (3:1)
Pedigree: inheritance of sex-linked genes XY XX X-linked
Meiotic recombination (1) • Crossing over • For genetic diversity • Unequal crossing over possible when chromosomes are not properly aligned
Meiotic recombination (2) • Tetrad • Synapsis (synaptonemal complex) • Chiasmata
Linkage group • Always on the same chromosome • Should be <50%
Nucleic acids (1) Base + sugar = nucleoside (deoxy- or ribo-) + phosphate = nucleotide (deoxy- or ribo-)
Nucleic acids (2) Phosphodiester linkage
Nucleic acids (3) See Table 3.01
dsDNA: double helix • RNA • Single-stranded • DNA • Double-stranded • Antiparallel • Double-helix, right-handed (clockwise)
Base paring and complementary strands • Base paring • Hydrogen bond • Complementary strands • To inherit genetic information • For gene duplication
Melting and annealing of DNA • Melting (denaturation): temp ↑ • Annealing (renaturation): temp↓, slowly, 20-25 °C below Tm • GC ratio or GC content ↑ Tm ↑
Chromosome (1) • Chromosome • Large DNA containing genes • Chromatin • DNA + protein (histone) • Prokaryotic chromosome • No intron • Operon: gene cluster
Chromosome (2) • Eukaryotic chromosome • Contains centromere and telomere • Replication of chromosome • Kinetochore: binds to centromere and microtubule during cell division • Role of telomerase Kinetochore (red) Chromosome (blue) Microtubule (green) From Google image
Central dogma • Flow of genetic information • Transcription pattern • Prokaryote vs. eukaryote
Translation (1) • Bacterial ribosome (70S) • Large subunit (50S) • 5S, 23S rRNA • Small subunit (30S) • 16S rRNA S = sedimentation coefficient, Svedberg unit
Codon and anticodon • Genetic code: 64 codons 20 amino acids • tRNA: contains anticodon
Translation (2) • Charged tRNA: with amino acid • Ribosome elongates polypeptide chain
Non-translated RNA • rRNA: ribosomal • tRNA: transfer (amino acid ribosome) • snRNA: small nuclear, processing of mRNA, RNA splicing • gRNA: guide, for RNA editing (insertion/deletion of U) • aRNA: antisense, single-stranded RNA complementary to mRNA, inhibit translation • Ribozyme: ribonucleic acid enzyme • Regulatory RNA: regulation of gene expression • Recognition RNA: recognition of short DNA sequence
Amino acid to polypeptide (alpha carbon) N-terminus (amino) C-terminus (carboxy)
Four organization levels of protein structure • Primary: • Linear • Secondary: • Initial folding due to hydrogen bonding (α-helix, β-sheet) • Tertiary: • 3-D conformation • Quaternary: • Assembly of several polypeptide chains
Protein function (1) • Folding generation of active site • Enzyme
Protein function (2) • Structural protein: e.g., microtubule • Enzyme • Regulatory protein • Transport protein: e.g., ion channel
X-ray crystallography • Hanging drop method