How to make a punnett square A step

How to make a punnett square A step by step method

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.

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?

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

Step 2 Determine the genotypes of the parents. ____x_____ Place the alleles for the r 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 r mom on the side. R R

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

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

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?

Let’s Practice Homozygous AA ____ HO Bb ____ HE HE Cc ____ HE Dd ____ (HO) or Heterozygous (HE) Ee ____ HE ff ____ HO HO GG ____ HO HH ____

Determine Phenotype Purple flowers are dominant to white flowers Brown eyes are dominant to blue eyes Brown Purple PP _______ BB ______ Purple Brown Pp _______ Bb ______ White Blue pp _______ bb ______

For each phenotype list the genotype Straight hair is dominant to curly. Pointed heads are dominant to round heads. ______ SS straight Ss ______ ss straight ______ curly ______ PP pointed Pp ______ pp pointed ______ round

Problem #1 Step 1 In Draw punnett square 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?

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

Problem #1 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? Ss ____ Ss x ____ S s s In Multiply sides to get possible offspring Ss ss S Step 3 SS Ss

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

Problem #2 3 Interpret Multiply Determine Parent genotypes 12 Draw punnett square Step 4 the possible offspring Square. Pants rr Rr x ____ recently met Sponge. Susie ____ Roundpants at a dance. R r Sponge. Bob is heterozygous for his square shape, but Sponge. Susie is round Rr rr (recessive). What is the ratio of round to square pants? r r Sponge. Bob 2: 2 Rr rr

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

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.

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

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. Yy. Rr x Yy. Rr

Step 3 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: Yy. Rr First- YR Outside- Yr Inside- y. R Last- yr Gremlin Yy. Rr

Step 4 Write all of the possible YR combinations of alleles on the sides and top of YR the punnett square. YR Yr y. R yr Yr y. R yr

Step 5 YR Yr through the YYRR YYRr results and determine YR Yellow, round what the phenotype of YYRr YYrr Yr Yellow, each offspring would round wrinkled Yy. RR Yy. Rr be Go y. R yr Yy. RR Yy. Rr Yellow, round Yy. Rr Yyrr Yellow, round Yellow, wrinkled yy. RR yy. Rr Yellow, round Green, round Yy. Rr Yyrr yy. Rr Yyrr Yellow, round Yellow, wrinkled Green, round Green, wrinkled

Step 6 YR Yr out the YYRR YYRr phenotypic ratio or Yellow, YR Yellow round answer whatever YYRr YYrr Yellow, question they ask you. Yr Yellow, round wrinkled Figure 9: 3: 3: 1 Example: what are the chances of having a yellow and wrinkled pea? 3/16 y. R yr Yy. RR Yy. Rr Yellow, round Yy. Rr Yyrr Yellow, round Yellow, wrinkled Yy. RR Yy. Rr yy. RR yy. Rr Yellow, round Green, round Yy. Rr Yyrr yy. Rr Yyrr Yellow, round Yellow, wrinkled Green, round Green, wrinkled

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 Tt. Yy First-TY Outside- Ty Inside- t. Y Last- ty Gremlin Tt. Yy

Problem #4 3 5 Answer and Analyze 4 punnett Determine results gametes and place on square 12 Draw square Determine genotypes Step 6 question(s) the alpha male and alpha female of a wolf pack are nnbb Nn. Bb ____ x ____ black with blue eyes and normal nb nb colored with brown eyes, Nn. Bb respectively. Assume further that normal, normal coat color (N) is dominant brown Bb to black (n) and brown eyes (B) Nnbb normal, are dominant to blue (b). The blue female is also heterozygous for nn. Bb Bb Bb black, both traits. brown What fraction of the offspring nnbb could have the following black, blue genotypes? nb n. B Nb NB Suppose NNBB: 0/16 Nn. Bb: 4/16 nnbb: 4/16