1. THE DIHYBRID CROSS Studying the inheritance of two traits simultaneously © 2007 Paul Billiet ODWSODWS

2. Student Moving Demo… 4 students 2 male 2 female Each Pair (male and female) represent a possible gene we can inherit from either dad (male) or mom (female) Traits considered = eye color & height What are the possible combinations?

3. What are the possible combinations of these traits? T or tB or bPhenotype

4. Mendel’s peas CharacterTraitAllele Seed shapeRoundR Wrinkledr Cotyledon colourYellowY Greeny © 2007 Paul Billiet ODWSODWS

5. Combinations GenotypePhenotype RRYYRound Yellow RRYyRound Yellow RrYYRound Yellow RrYyRound Yellow RRyyRound Green RryyRound Green rrYYWrinkled Yellow rrYyWrinkled Yellow rryyWrinkled Green © 2007 Paul Billiet ODWSODWS How is this possible?

6. MENDELS LAW OF INDEPENDENT ASSORTMENT It appears that the inheritance of seed shape has no influence over the inheritance of seed color The two characters are inherited INDEPENDENTLY The pairs of alleles that control these two characters assort themselves independently © 2007 Paul Billiet ODWSODWS

7. Mendel & Meiosis The pairs of chromosomes can be lined up in different ways at Anaphase 1 © 2007 Paul Billiet ODWSODWS

8. PPhenotypesRound Yellow seed XWrinkled Green seed (Pure bred) GenotypesRRYYrryy meiosis GametesRYry fertilization F1F1 PhenotypesRrYy(Selfed) GenotypesRound Yellow Proportions100% Dihybrid cross genetic diagram © 2007 Paul Billiet ODWSODWS AND CHECK OUT THE GENERATIONAL NOTATION…

9. F1F1 PhenotypesRrYy(Selfed) GenotypesRound Yellow Proportions100% meiosis GametesYy RRYRy rrYry Dihybrid cross genetic diagram © 2007 Paul Billiet ODWSODWS

10. GametesYy RRYRy rrYry fertilization F2F2 GenotypesRYRyrYry RYRRYYRRYyRrYYRrYy RyRRYyRRyyRrYyRryy rYRrYYRrYyrrYYrrYy ryRrYyRryyrrYyrryy Dihybrid cross genetic diagram © 2007 Paul Billiet ODWSODWS HINT: Do a Punnett square for each parent’s 2 traits first!!!

11. Dihybrid cross proportions PhenotypesProportions Round Yellow9/16 or56.25% Round Green Wrinkled Yellow Wrinkled Green © 2007 Paul Billiet ODWSODWS

12. Dihybrid cross proportions PhenotypesProportions Round Yellow9/16 or56.25% Round Green3/16 or18.75% Wrinkled Yellow3/16 or18.75% Wrinkled Green1/16 or6.25% © 2007 Paul Billiet ODWSODWS

13. Dihybrid test cross In monohybrid crosses, to know if a dominant trait is homozygous (RR) or heterozygous (Rr) it is necessary to carry out a test cross This is done with a homozygous recessive (rr) individual The same is true for a dihybrid cross where the test cross is made with an individual which is homozygous recessive for both characters (rryy) © 2007 Paul Billiet ODWSODWS

14. Dihybrid test cross PhenotypesRound YellowXWrinkled Green GenotypesRrYyrryy GametesRY, Ry, rY, ryry GenotypesRYRyrYry RrYyRryyrrYyrryy PhenotypesRound Yellow Round Green Wrinkled Yellow Wrinkled Green Proportions1/4 or 25% © 2007 Paul Billiet ODWSODWS