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Genetic Diagrams

Genetic Diagrams. Noadswood Science, 2012. Genetic Diagrams. To understand how to be able to construct genetic diagrams. BB. bb. B. B. b. b. B b. B b. B b. B b. Genetic Diagrams. Genetic diagrams show the possible genes for offspring

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Genetic Diagrams

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  1. Genetic Diagrams Noadswood Science, 2012

  2. Genetic Diagrams • To understand how to be able to construct genetic diagrams BB bb B B b b Bb Bb Bb Bb

  3. 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

  4. 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

  5. Hamster Cross Example • Crossing a thoroughbred crazy hamster (bb) and a thoroughbred normal hamster (BB) Normal hamster Crazy hamster

  6. Hamster Cross Example • Crossing a thoroughbred crazy hamster (bb) and a thoroughbred normal hamster (BB) (both homozygous) – all offspring normal Parents NormalCrazy Parent’s alleles Gamete’s alleles Possible combinations BB bb B B b b Bb Bb Bb Bb

  7. 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 NormalNormal Parent’s alleles Gamete’s alleles Possible combinations Bb Bb B b B b BB Bb Bb bb

  8. 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) Male Female

  9. Sex Cross Example • Probability of male / female offspring – 50:50 Parents MaleFemale Parent’s alleles Gamete’s alleles Possible combinations XY XX X Y X X XX XX XY XY

  10. Genetic Diagrams – Question • Eye colour can be brown and blue (simplistic) – in this example brownis 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

  11. Eye Colour – Homozygous • Crossing a homozygous blue-eyed person (bb) and a homozygous brown-eyedperson (BB) Brown-eyed - homozygous Blue-eyed - homozygous

  12. Eye Colour • Crossing a homozygous blue-eyed person (bb) and a homozygous brown-eyedperson (BB) – all offspring brown-eyed Parents Brown-eyedBlue-eyed Parent’s alleles Gamete’s alleles Possible combinations BB bb B B b b Bb Bb Bb Bb

  13. Eye Colour – Heterozygous • Crossing two heterozygous brown-eyedindividuals (Bb) Brown-eyed - heterozygous Brown-eyed - heterozygous

  14. Eye Colour • Crossing two heterozygous brown-eyedindividuals (Bb) – 3x brown-eyed(75%) and 1x blue-eyed (25%) Parents Brown-eyedBrown-eyed Parent’s alleles Gamete’s alleles Possible combinations Bb Bb B b B b BB Bb Bb bb

  15. Eye Colour – Hetero & Homozygous • Crossing one heterozygous brown-eyedindividual (Bb) and one homozygous blue-eyed individual (bb) Blue-eyed – homozygous Brown-eyed - heterozygous

  16. Eye Colour • Crossing one heterozygous brown-eyedindividual (Bb) and one homozygous blue-eyed individual (bb)– 50:50 Parents Brown-eyedBlue-eyed Parent’s alleles Gamete’s alleles Possible combinations Bb bb B b b b Bb Bb bb bb

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