1. Genetic Diagrams Noadswood Science, 2012

2. Genetic Diagrams To understand how to be able to construct genetic diagrams BBbb BBbb BbBbBbBbBbBbBbBb Sunday, August 23, 2015

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) BB bBbBbBbBb bBbBbBbBb 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 Normal Crazy Parent’s alleles Gamete’s alleles Possible combinations BBbb BBbb BbBbBbBbBbBbBbBb

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 Normal Normal Parent’s alleles Gamete’s alleles Possible combinations BbBbBbBb BbBb BBBbBbBbBbbb

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) XY XXXXYXY X XYXY Male Female

9. Sex Cross Example Probability of male / female offspring – 50:50 Parents Male Female Parent’s alleles Gamete’s alleles Possible combinations XYXYXX XYXX XYXYXYXY

10. 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

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

12. 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 Parent’s alleles Gamete’s alleles Possible combinations BBbb BBbb BbBbBbBbBbBbBbBb

13. Eye Colour – Heterozygous Crossing two heterozygous brown-eyed individuals (Bb) Bb BBBBbBb bBbBbbb Brown-eyed - heterozygous

14. Eye Colour Crossing two heterozygous brown-eyed individuals (Bb) – 3x brown-eyed (75%) and 1x blue-eyed (25%) Parents Brown-eyed Brown-eyed Parent’s alleles Gamete’s alleles Possible combinations BbBbBbBb BbBb BBBbBbBbBbbb

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

16. Eye Colour Crossing one heterozygous brown-eyed individual (Bb) and one homozygous blue-eyed individual (bb) – 50:50 Parents Brown-eyed Blue-eyed Parent’s alleles Gamete’s alleles Possible combinations BbBbbb Bbbb BbBbBbBb