Gene regulation Gene regulation NUCLEUS CYTOPLASM R S

Gene regulation

Gene regulation NUCLEUS CYTOPLASM R. S. Winning, 2003

Gene regulation Transcription: regulated by activators (transcription factors) and repressors (rare in eukaryotes) Examples: heat shock transcription factor always present; becomes active when temperature changes steroid hormones bind directly to TF to activate it peptide hormones bind to cell membrane and initiate series of reactions within the cell to activate TF

Gene regulation transcription: regulated by activators (transcription factors) and repressors (rare in eukaryotes) RNA processing: different exons may be used within one gene, producing different protein products

Gene regulation transcription: regulated by activators (transcription factors) and repressors (rare in eukaryotes) RNA processing: different exons may be used within one gene, producing different protein products m. RNA longevity: m. RNA translates as long as it is intact ‘lifespan’ encoded in the 3' UTR sequence AUUUA signals early degradation

Gene regulation transcription: regulated by activators (transcription factors) and repressors (rare in eukaryotes) RNA processing: different exons may be used within one gene, producing different protein products m. RNA longevity: m. RNA translates as long as it is intact ‘lifespan’ encoded in the 3' UTR sequence AUUUA signals early degradation translation: m. RNA may exist without being translated (not well understood)

Mutation potential phenotypic effects of mutation: morphological trait – change in color, size nutritional or biochemical variation – loss of ability to synthesize a protein - synthesis of different versions of a protein change in behavior – e. g. , fruitflies - lose ability to recognize mate gender changes in gene regulation - gene turned off, or on lethality – loss of essential function

Mutation Spontaneous mutations – errors in translation, ~ every 106 bases repaired during translation by DNA polymerase ‘checking’ Induced mutations – due to mutagens

Point mutations Single base substitutions transitions - purine to purine, or pyrimidine to pyrimidine transversions - purine with a pyrimidine or vice versa.

Point mutations Single base substitutions transitions - purine to purine, or pyrimidine to pyrimidine transversions - purine with a pyrimidine or vice versa. The fat cat ate the hot dog. The fat car ate the hot dog. The fat cat ate the hot hog. small change in meaning, still readable no change (synonymous or silent mutations) single amino acid change (missense mutation)

Point mutations frameshift mutations insertions deletions

Point mutations frameshift mutations insertions deletions The fat cat ate the hot dog. The fma tca tat eth eho tdo g. profound change Thf atc ata tet heh otd og includes change in stop codon: The fat cat ate the hot dog how why fry hot cat the…

Mutation changes in larger segments of genome - tandem duplications addition of duplicate CAG sequences results in Huntington’s chorea - ploidy, aneuploidy

ploidy = number of chromosome sets in cell haploid – 1 (gametes) diploid − 2 (most cells) triploid – 3 (sterile) tetraploid – 4. . etc. Xenopus tropicalis Xenopus laevis Xenopus muelleri Xenopus ruwensoriensis 2 N = 20 2 N = 36 2 N = 72 2 N = 108 diploid tetraploid octaploid dodecaploid

ploidy = number of chromosome sets in cell haploid – 1 (gametes) diploid − 2 (most cells) triploid – 3 (sterile) tetraploid – 4. . etc. plants tend to have more ploidy levels – can overcome sterility with vegetative reproduction higher ploidy -> larger cells, more ‘product’ - yeast - wheats autopolyploidy vs. allopolyploidy

euploidy = correct number of chromosome sets in cell polyploidy aneuploidy = incomplete set of chromosomes usually due to non-disjunction during meiosis Down’s syndrome (trisomy 21) Patau’s syndrome (trisomy 13) Turner’s syndrome (monosomy of X chromosome) Klinefelter syndrome (trisomy of sex chromosomes, XXY)

euploidy = correct number of chromosome sets in cell polyploidy aneuploidy = incomplete set of chromosomes usually due to non-disjunction during meiosis Down’s syndrome (trisomy 21) Patau’s syndrome (trisomy 13) Turner’s syndrome (monosomy of X chromosome) Klinefelter syndrome (trisomy of sex chromosomes, XXY) which is likely to have more severe effects, monosomy or trisomy?

Inversions – part of chromosome is flipped by 180

Translocations – non-homologous chromosomes exchange material (not always symmetrically)

euploidy = correct number of chromosome sets in cell polyploidy aneuploidy = incomplete set of chromosomes usually due to non-disjunction during meiosis Down’s syndrome (trisomy 21) Patau’s syndrome (trisomy 13) Turner’s syndrome (monosomy of X chromosome) Klinefelter syndrome (trisomy of sex chromosomes, XXY) loss/variation/rearrangement of portions of chromosome Cri-du-chat syndrome (loss of part of arm of chromosome 5)

Mutation Somatic cell mutations – affect only individual Gametic (germline) cell mutations – heritable (e. g. , cancer is largely unimportant evolutionarily)