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How to make a Punnett square

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Presentation on theme: "How to make a Punnett square"— Presentation transcript:

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 Phenotypic Ask your self: Ask yourself:
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 AA ____ Bb ____ Cc ____ Dd ____
Homozygous (HO) or Heterozygous (HE) AA ____ Bb ____ Cc ____ Dd ____ Ee ____ ff ____ GG ____ HH ____ HO HE HE HO HE HO HE HO

10 Determine Phenotype Purple Brown Purple Brown White Blue
Purple flowers are dominant to white flowers PP _____________ Pp _____________ pp _____________ Brown eyes are dominant to blue eyes BB ____________ Bb ____________ bb ____________ Purple Brown Purple Brown White Blue

11 For each phenotype list the genotype
Straight hair is dominant to curly. ____________ straight ____________ straight ____________ curly Pointed heads are dominant to round heads. ____________ pointed ____________ pointed ____________ round 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 Step 2 Determine the genotype of parents, and place alleles on punnett square 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 S s

14 Problem #1 Step 3 Multiply sides to get possible offspring Ss Ss S s
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 1 Draw punnett square
Step 4 Interpret the possible offspring Step 3 Multiply Step 2 Determine Parent genotypes 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 Go through the results and determine what the phenotype of each offspring would be YR 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 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 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 F.O.I.L TtYy First- Outside- Inside- Last- Gremlin TtYy TY Ty tY ty

25 Problem #4 Step 3 and 4 Determine gametes and place on square
Step 1 Draw punnett square Step 7 Answer question(s) Step 5 Fill in the square Step 2 Determine genotypes Step 6 Analyze results 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. ________ x ________ BBTT bbtt BT BT BT BT 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 Bb BbTt chestnut, trotting BbTt chestnut, trotting Bb BbTt chestnut, trotting bt BbTt chestnut, trotting BbTt chestnut, trotting BbTt chestnut, trotting BbTt chestnut, trotting bt What percentage of offspring could be chestnut and pacing? 0%

26 Problem #5 Step 3 and 4 Determine gametes and place on square
Step 1 Draw punnett square Step 6 Analyze results Step 5 Fill in the square Step 2 Determine genotypes Step 7 Answer question(s) 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? ________ x ________ nnbb NnBb nb nb nb nb 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 Bb nnBb black, brown nnBb black, brown Bb nnBb black, brown nB nnbb black, blue nnbb black, blue nnbb black, blue nnbb black, blue nb NNBB: NnBb: nnbb: 0/16 4/16 4/16

27 Problem #6 Step 1 Draw punnett square
Step 3 and 4 Determine gametes and place on square Step 5 Fill in the square Step 2 Determine genotypes 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 FfSs FS Fs fS fs 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 9:3:3:1 Step 7 Answer question(s) Step 5 Fill in the square
Step 6 Analyze results 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 FfSs FS Fs fS fs 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 Bb FfSS fresh, shallow ffSS rotted, shallow Bb ffSs rotted, shallow fS FfSS fresh, shallow Ffss fresh, deep ffSs rotted, shallow ffss rotted, deep fs Fresh/shallow: fresh/deep: rotted/shallow: rotted/deep 9:3:3:1

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