How to make a punnett square

1. How to make a punnett square A step by step method

2. What is a punnett square? • A punnett square is a diagram used to try to predict the outcome of a cross between 2 parents. • It does not tell us what will happen, but it does tell us the likelihood that something will happen.

3. Monohybrid crosses • These are crosses that only look at a single trait • Ex: hair color, eye color, albinism • Ex: What are the chances that my baby will have brown eyes?

4. Step 1 • Draw a box and divide it into 4 squares. These squares represent the possible offspring

5. Step 2 • Determine the genotypes of the parents. ____x_____ • Place the alleles for the genotypes of the parents on the sides and top of the square. • As a general rule, we put the dad on the top and the mom on the side. R R r r

6. Step 3 • Now you multiply the sides with the top to get the genotype of the 4 offspring boxes. R R Rr r Rr Rr Rr r

7. Step 4 • Now you can see what the genotypes of the offspring would be. • In this case there is a 100% chance of the offspring being heterozygous for the trait because all 4 out of 4 boxes are capital, lower case. R R Rr r Rr Rr Rr r

8. Ratios • Genotypic • Ask your self: • How many homozygous dominants? • How many heterozygous? • How many homozygous recessives? • Phenotypic • Ask yourself: • How many dominant phenotypes? • How many recessive phenotypes?

9. Let’s Practice • Homozygous (HO) or Heterozygous (HE) HO HE HE HO HO HE HE HO

10. Determine Phenotype Brown Purple Purple Brown White Blue

11. For each phenotype list the genotype SS PP Ss Pp ss pp

12. Problem #1 Draw punnett square Step 1 • In pea plants, spherical seeds (S) are dominant to dented seeds (s). In a genetic cross of two plants that are heterozygous for the seed shape trait, what fraction of the offspring should have spherical seeds?

13. Problem #1 Determine the genotype of parents, and place alleles on punnett square Step 2 ________ x ________ Ss Ss • In pea plants, spherical seeds (S) are dominant to dented seeds (s). In a genetic cross of two plants that are heterozygous for the seed shape trait, what fraction of the offspring should have spherical seeds? S s S s

14. Problem #1 Multiply sides to get possible offspring Step 3 ________ x ________ Ss Ss • In pea plants, spherical seeds (S) are dominant to dented seeds (s). In a genetic cross of two plants that are heterozygous for the seed shape trait, what fraction of the offspring should have spherical seeds? S s Ss ss S s SS Ss

15. Problem #1 Interpret the possible offspring Step 4 ________ x ________ Ss Ss • In pea plants, spherical seeds (S) are dominant to dented seeds (s). In a genetic cross of two plants that are heterozygous for the seed shape trait, what fraction of the offspring should have spherical seeds? S s Ss ss S s SS Ss 3/4

16. Problem #2 Step 3 Multiply Step 2 Determine Parent genotypes Step 4 Interpret the possible offspring Step 1 Draw punnett square ________ x ________ rr Rr • SpongeBob SquarePants recently met SpongeSusie Roundpants at a dance. SpongeBob is heterozygous for his square shape, but SpongeSusie is round (recessive). What is the ratio of round to square pants? R r Rr rr r r Rr rr 2:2

17. Problem #3 Step 2 Determine Parent genotypes Step 3 Multiply BB bb B B Step 4 Interpret the possible offspring Step 1 Draw punnett square ________ x ________ • Squidward is purebred for light blue skin, which is the dominant trait for body color. He recently married a nice girl who has light green skin, which is a recessive trait. Create a Punnett square to show the possibilities that would result if Squidward and his new bride had children. • What percentage of Squidward’s offspring could be green? Bb Bb b b Bb Bb 0%

18. Dihybrid crosses • Dihybrid crosses are punnett squares used to predict the probability of an offspring having 2 traits at the same time. • Ex: What are the chances of my baby having brown eyes AND blond hair.

19. Step 1 • Draw a box and divide it into 16 squares.

20. Step 2 • Determine the genotypes of the parents • Ex: cross two pea plants that are heterozygous for yellow peas and round peas. • Yellow is dominant to green and round is dominant to wrinkled. • YyRr x YyRr

21. Step 3 Gremlin • Determine all of the possible gamete combinations for each parent by using the F.O.I.L. or Gremlin method • FOIL= first, outside, inside last • Ex: YyRr • First- YR • Outside- Yr • Inside- yR • Last- yr YyRr

22. Step 4 • Write all of the possible combinations of alleles on the sides and top of the punnett square. • YR • Yr • yR • yr YR Yr yR yr YR Yr yR yr

23. Step 5 yr • Go through the results and determine what the phenotype of each offspring would be YR Yr yR YYRR Yellow round YYRr Yellow, round YyRR Yellow, round YyRr Yellow, round YR YYRr Yellow, round YYrr Yellow,wrinkled YyRr Yellow, round Yyrr Yellow, wrinkled Yr YyRR Yellow, round YyRr Yellow, round yyRR Green, round yyRr Green, round yR YyRr Yellow, round Yyrr Yellow, wrinkled yyRr Green, round Yyrr Green, wrinkled yr

24. Step 6 yr • Figure out the phenotypic ratio or answer whatever question they ask you. • 9:3:3:1 • Example: what are the chances of having a yellow and wrinkled pea? • 3/16 YR Yr yR YYRR Yellow round YYRr Yellow, round YyRR Yellow, round YyRr Yellow, round YR YYRr Yellow, round YYrr Yellow,wrinkled YyRr Yellow, round Yyrr Yellow, wrinkled Yr YyRR Yellow, round YyRr Yellow, round yyRR Green, round yyRr Green, round yR YyRr Yellow, round Yyrr Yellow, wrinkled yyRr Green, round Yyrr Green, wrinkled yr

25. Let’s Practice • Determine the gametes for the following cross: heterozygous tall plant with heterozygous yellow seeds with another of the same genes. Tall and yellow are dominant Gremlin TtYy • F.O.I.L • TtYy • First- • Outside- • Inside- • Last- TY Ty tY ty

26. Step 5 Analyze results Step 2 Determine genotypes Step 6 Answer question(s) Step 3 and 4 Determine gametes and place on square Problem #4 nnbb NnBb nb nb nb nb NNBB: NnBb: nnbb: ________ x ________ Step 1 Draw punnett square NnBb normal, brown NnBb normal, brown NnBb normal, brown NnBb normal, brown NB • Suppose the alpha male and alpha female of a wolf pack are black with blue eyes and normal colored with brown eyes, respectively. Assume further that normal coat color (N) is dominant to black (n) and brown eyes (B) are dominant to blue (b). The female is also heterozygous for both traits. • What fraction of the offspring could have the following genotypes? Bb Bb Nnbb normal, blue Nnbb normal, blue Nnbb normal, blue Nnbb normal, blue Nb nnBb black, brown nnBb black, brown nnBb black, brown nnBb black, brown Bb Bb nB nnbb black, blue nnbb black, blue nnbb black, blue nnbb black, blue nb 4/16 4/16 0/16