1. GENERAL GENETICS (PRACTICAL SESSION) BIO221 LECTURER ALSHEHRI, DOKHNAH SAEED DALSHEHRI@UT.EDU.SA Alshehri, Dikhnah Saeed

2. THE 7 TH LAB THE DIHYBRID CROSS STUDYING THE INHERITANCE OF TWO CHARACTERS SIMULTANEOUSLY © 2007 Paul Billiet ODWSODWS Alshehri, Dikhnah Saeed

3. OUTLINES: What is the di-hybrid cross?. Mendel’s Peas. Some practical exercise And class activates. Alshehri, Dikhnah Saeed

4. MENDEL’S PEAS CharacterTraitAllele Seed shapeRoundR Wrinkledr Seed colourYellowY Greeny © 2007 Paul Billiet ODWSODWS Alshehri, Dikhnah Saeed

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 Alshehri, Dikhnah Saeed

6. IS THE INHERITANCE OF ONE CHARACTER AFFECTED BY THE INHERITANCE OF ANOTHER? P PhenotypesRound Yellow xWrinkled Green (Pure Bred) F 1 PhenotypesAll Round Yellow (Selfed) F 2 Phenotypes Seedcolour YellowGreenTOTALRATIO SeedRound315108423 shapeWrinkled10132133 TOTAL416140556 RATIO © 2007 Paul Billiet ODWSODWS Alshehri, Dikhnah Saeed

7. A DIHYBRID CROSS CAN BE TREATED AS TWO SEPARATE MONOHYBRID CROSSES THE EXPECTED PROBABILITY OF EACH TYPE OF SEED CAN BE CALCULATED: PROBABILITY OF AN F 2 SEED BEING ROUND = 75% OR ¾ PROBABILITY OF AN F 2 SEED BEING WRINKLED = PROBABILITY OF AN F 2 SEED BEING YELLOW = PROBABILITY OF AN F 2 SEED BEING GREEN = © 2007 Paul Billiet ODWSODWS Alshehri, Dikhnah Saeed

8. A dihybrid cross can be treated as two separate monohybrid crosses The expected probability of each type of seed can be calculated: Probability of an F 2 seed being round = 75% or ¾ Probability of an F 2 seed being wrinkled = 25% or ¼ Probability of an F 2 seed being yellow = 75% or ¾ Probability of an F 2 seed being green = 25% or ¼ © 2007 Paul Billiet ODWSODWS Alshehri, Dikhnah Saeed

9. Therefore Probability of an F 2 seed being round and yellow = ¾ x ¾ = 9/16 =56.25% Probability of an F 2 seed being round and green = Probability of an F 2 seed being wrinkled and yellow = Probability of an F 2 seed being wrinkled and green = © 2007 Paul Billiet ODWSODWS Alshehri, Dikhnah Saeed

10. THEREFORE Probability of an F 2 seed being round and yellow = ¾ x ¾ = 9/16 =56.25% Probability of an f 2 seed being round and green = ¾ x ¼ = 3/16 =18.75% Probability of an f 2 seed being wrinkled and yellow = ¼ x ¾ = 3/16 =18.75% Probability of an f 2 seed being wrinkled and green = ¼ x ¼ =1/16 =6.25% © 2007 Paul Billiet ODWSODWS Alshehri, Dikhnah Saeed

11. Predicting how many seeds we could expect to get in a sample We could expect What Mendel observed 556 x 9/16 round yellow313315 556 x 3/16 round green108 556 x 3/16 wrinkled yellow101 556 x 1/16 wrinkled green32 © 2007 Paul Billiet ODWSODWS Alshehri, Dikhnah Saeed

12. PREDICTING HOW MANY SEEDS WE COULD EXPECT TO GET IN A SAMPLE We could expect What Mendel observed 556 x 9/16 round yellow313315 556 x 3/16 round green104108 556 x 3/16 wrinkled yellow104101 556 x 1/16 wrinkled green3532 © 2007 Paul Billiet ODWSODWS Alshehri, Dikhnah Saeed

13. The law of independent assortment It appears that the inheritance of seed shape has no influence over the inheritance of seed colour The two characters are inherited INDEPENDENTLY The pairs of alleles that control these two characters assort themselves independently © 2007 Paul Billiet ODWSODWS Alshehri, Dikhnah Saeed

14. MENDEL & MEIOSIS The pairs of chromosomes could orientate in different ways at anaphase 1 © 2007 Paul Billiet ODWSODWS Alshehri, Dikhnah Saeed

15. PPhenotypesRound Yellow seed XWrinkled Green seed (Pure bred) GenotypesRRYYrryy meiosis GametesRYry fertilisation F1F1 PhenotypesRrYy(Selfed) GenotypesRound Yellow Proportions100% DIHYBRID CROSS GENETIC DIAGRAM © 2007 Paul Billiet ODWSODWS Alshehri, Dikhnah Saeed

16. F1F1 PhenotypesRrYy(Selfed) GenotypesRound Yellow Proportions100% meiosis GametesYy RRYRy rrYry DIHYBRID CROSS GENETIC DIAGRAM © 2007 Paul Billiet ODWSODWS Alshehri, Dikhnah Saeed

17. GametesYy RRYRy rrYry fertilisation F2F2 GenotypesRYRyrYry RYRRYYRRYyRrYYRrYy RyRRYyRRyyRrYyRryy rYRrYYRrYyrrYYrrYy ryRrYyRryyrrYyrryy DIHYBRID CROSS GENETIC DIAGRAM © 2007 Paul Billiet ODWSODWS Alshehri, Dikhnah Saeed

18. DIHYBRID CROSS PROPORTIONS PhenotypesProportions Round Yellow9/16 or56.25% Round Green Wrinkled Yellow Wrinkled Green © 2007 Paul Billiet ODWSODWS Alshehri, Dikhnah Saeed

19. 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 Alshehri, Dikhnah Saeed

20. 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 Alshehri, Dikhnah Saeed

21. 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 Alshehri, Dikhnah Saeed

22. CLASS ACTIVITY: Set up a punnett square using the following information: ·∙ Dominate allele for black fur in guinea pigs = B ·∙ Recessive allele for white fur in guinea pigs =b ·∙ Dominate allele for rough fur in guinea pigs = R ·∙ Recessive allele for smooth fur in guinea pigs = r ·∙ Cross a heterozygous parent (bbrr) with a heterozygous parent (bbrr) Alshehri, Dikhnah Saeed

23. Using the punnett square produced in the previous question: A. What is the probability of producing guinea pigs with black, rough fur? What is/are the possible genotype(s)? B. What is the probability of producing guinea pigs with black, smooth fur? What is/are the possible genotype(s)? C. What is the probability of producing guinea pigs with white, rough fur? What is/are the possible genotype(s)? D. What is the probability of producing guinea pigs with white, smooth fur? What is/are the possible genotype(s)? Alshehri, Dikhnah Saeed

24. EXERCISE 1 A brown-eyed, long-winged fly mated with a red- eyed, long-winged fly. The progeny were: 51 long, red 18 short, red 53 long, brown 16 short, brown What are the genotypes of the parents? Alshehri, Dikhnah Saeed

25. EXERCISE 2 Two rough black guinea-pigs bred together have two offsprings; one of them roughly white and the other smooth black. If these same parents were further bred together, what offspring would you expect for them? Alshehri, Dikhnah Saeed

26. EXERCISE 3 1. In guinea-pigs, black fur (B) is dominant over albino (b) and course hair (R) is dominant over smooth hair ( r ). A. What are the genotypes and phenotypes of a cross between homozygous black animal, course hair and an albino animal, smooth hair. B. What are the genotypes and phenotypes of the F2 generation if two of the offspring from the F1 generation crossed. Alshehri, Dikhnah Saeed