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Transcript
Genetic Diagrams Noadswood Science, 2012 Tuesday, May 23, 2017 Genetic Diagrams • To understand how to be able to construct genetic diagrams BB bb B B b b Bb Bb Bb Bb Genetic Diagrams • Genetic diagrams show the possible genes for offspring • Alleles are different versions of the same gene, and most of the time there are two copies for each gene (one from each parent) • If they’re different alleles one might be ‘expressed’ by the organism (dominant allele) • In genetic diagrams letters are used to represent genes – dominant alleles are always shown with CAPITAL LETTERS, whilst recessive alleles are shown with lower case Genetic Diagrams – Example • Hamster can be either normal or crazy – in this example normal is dominant (B) and crazy is recessive (b) • Hamster normal gene – B • Hamster crazy gene – b • A crazy hamster (recessive characteristic) must have both alleles as recessive – bb • A normal hamster (dominant characteristic) can have two combinations: either both dominant – BB, or one dominant and one recessive – Bb Hamster Cross Example • Crossing a thoroughbred crazy hamster (bb) and a thoroughbred normal hamster (BB) Crazy hamster Normal hamster B B b Bb Bb b Bb Bb Hamster Cross Example • Crossing a thoroughbred crazy hamster (bb) and a thoroughbred normal hamster (BB) (both homozygous) – all offspring normal Parents Parent’s alleles Normal Crazy BB bb Gamete’s alleles B B b b Possible combinations Bb Bb Bb Bb Hamster Cross Example • If two of the heterozygous offspring were then crossed (Bb x Bb) then we would have 3x normal (75%) and 1x crazy (25%) Parents Normal Bb Parent’s alleles Gamete’s alleles Possible combinations Normal Bb B b B b BB Bb Bb bb Genetic Diagrams – Question • Complete the genetic cross to show the possible combination of gametes: ▫ Female produces two X gametes (XX) ▫ Male produces one X gamete (X) and one Y gamete (Y) Female Male X Y X XX XY X XX XY Sex Cross Example • Probability of male / female offspring – 50:50 Parents Parent’s alleles Gamete’s alleles Possible combinations Male Female XY XX X Y X X XX XX XY XY Genetic Diagrams – Question • Eye colour can be brown and blue (simplistic) – in this example brown is dominant (B) and blue is recessive (b) • Brown gene – B • Blue gene – b • An individual with blue eyes (recessive characteristic) must have both alleles as recessive – bb • An individual with brown eyes (dominant characteristic) can have two combinations: either both dominant – BB, or one dominant and one recessive – Bb Eye Colour – Homozygous • Crossing a homozygous blue-eyed person (bb) and a homozygous brown-eyed person (BB) Blue-eyed homozygous Brown-eyed - homozygous B B b Bb Bb b Bb Bb Eye Colour • Crossing a homozygous blue-eyed person (bb) and a homozygous brown-eyed person (BB) – all offspring brown-eyed Parents Brown-eyed Blue-eyed BB bb Parent’s alleles Gamete’s alleles B B b b Possible combinations Bb Bb Bb Bb Eye Colour – Heterozygous • Crossing two heterozygous brown-eyed individuals (Bb) Brown-eyed heterozygous Brown-eyed - heterozygous B b B BB Bb b Bb bb Eye Colour • Crossing two heterozygous brown-eyed individuals (Bb) – 3x brown-eyed (75%) and 1x blue-eyed (25%) Parents Brown-eyed Brown-eyed Bb Bb Parent’s alleles Gamete’s alleles Possible combinations B b B b BB Bb Bb bb Eye Colour – Hetero & Homozygous • Crossing one heterozygous brown-eyed individual (Bb) and one homozygous blue-eyed individual (bb) Brown-eyed heterozygous Blue-eyed – homozygous b b B Bb Bb b bb bb Eye Colour • Crossing one heterozygous brown-eyed individual (Bb) and one homozygous blue-eyed individual (bb) – 50:50 Parents Brown-eyed Blue-eyed Bb Parent’s alleles bb Gamete’s alleles B b b b Possible combinations Bb Bb bb bb
