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 • 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? • ________ x ________ Ss Ss S s S s

14. Problem #1 Multiply sides to get possible offspring Step 3 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? • ________ x ________ S s Ss ss S s SS Ss

15. Problem #1 Step 3 Multiply Step 2 Determine Parent genotypes Step 4 Interpret the possible offspring Step 1 Draw punnett square • 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? • ________ x ________ rr Rr R r Rr rr r r Rr rr 2:2

16. 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.

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

18. 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

19. 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

20. 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

21. Step 5 • Do the cross • Remember to keep all of one letter together and all of the 2nd letter together. YR Yr yR yr YR YYRR YYRr YyRR YyRr Yr Yyrr YYRr YyRr YYrr yR yyRr yyRR YyRr YyRR yr YyRr Yyrr yyRr yyrr

22. Step 6 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

23. Step 7 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

24. 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

25. Problem #4 Step 6 Analyze results Step 5 Fill in the square Step 7 Answer question(s) Step 2 Determine genotypes Step 3 and 4 Determine gametes and place on square BBTT bbtt What percentage of offspring could be chestnut and pacing? Step 1 Draw punnett square BT BT BT BT • ________ x ________ • In horses, black is dependent upon a dominant gene (B), and chestnut color upon its recessive allele(b). • The trotting gait is due to a dominant allele, (T), the pacing gait to its recessive allele, (t). • Cross a homozygous black, homozygous trotting horse with a chestnut, pacing horse. BbTt chestnut, trotting BbTt chestnut, trotting BbTt chestnut, trotting BbTt chestnut, trotting bt Bb Bb BbTt chestnut, trotting BbTt chestnut, trotting BbTt chestnut, trotting BbTt chestnut, trotting bt BbTt chestnut, trotting BbTt chestnut, trotting BbTt chestnut, trotting BbTt chestnut, trotting Bb Bb bt BbTt chestnut, trotting BbTt chestnut, trotting BbTt chestnut, trotting BbTt chestnut, trotting bt 0%

26. Problem #5 Step 6 Analyze results Step 5 Fill in the square Step 7 Answer question(s) Step 2 Determine genotypes Step 3 and 4 Determine gametes and place on square nnbb NnBb NNBB: NnBb: nnbb: Step 1 Draw punnett square nb nb nb nb • ________ x ________ • 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? NnBb normal, brown NnBb normal, brown NnBb normal, brown NnBb normal, brown NB 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

27. Problem #6 Step 5 Fill in the square Step 2 Determine genotypes Step 3 and 4 Determine gametes and place on square FfSs FfSs Step 1 Draw punnett square FS Fs fS fs • Carrion beetles lay their eggs in dead animals and then bury them in the ground until they hatch. Assume that the preference for fresh meat (F) is dominant to the preference for rotted meat and that the tendency to bury the meat shallow (S) is dominant to the tendency to bury the meat deep. Suppose a female and male carrion beetle heterozygous both traits mate. What is the phenotypic ratio? • ________ x ________ FFSS fresh, shallow FFSs fresh, shallow FfSS fresh, shallow FfSs fresh, shallow FS Bb Bb FFSs fresh, shallow FFss fresh, deep FfSS fresh, shallow Fs Bb Bb fS fs

28. Problem #6 Step 7 Answer question(s) Step 6 Analyze results Step 5 Fill in the square FfSs FfSs Fresh/shallow: fresh/deep: rotted/shallow: rotted/deep FS Fs fS fs • ________ x ________ • Carrion beetles lay their eggs in dead animals and then bury them in the ground until they hatch. Assume that the preference for fresh meat (F) is dominant to the preference for rotted meat and that the tendency to bury the meat shallow (S) is dominant to the tendency to bury the meat deep. Suppose a female and male carrion beetle heterozygous both traits mate. What is the phenotypic ratio? FFSS fresh, shallow FFSs fresh, shallow FfSS fresh, shallow FfSs fresh, shallow FS Bb Bb FFSs fresh, shallow FFss fresh, deep FfSS fresh, shallow Ffss fresh, deep Fs FfSS fresh, shallow FfSS fresh, shallow ffSS rotted, shallow ffSs rotted, shallow Bb Bb fS FfSS fresh, shallow Ffss fresh, deep ffSs rotted, shallow ffss rotted, deep fs 9:3:3:1