Punnett Squares Genotype/ Phenotype

Punnett Squares Genetics and Probability Note: Probability: is the possibility, or likelihood something will occur Point: It can be used to predict the results of genetic crosses

Punnett Squares Probability Points: *Usually written as a fraction of as a percentage *Previous events do not affect future outcomes *Each event happens independently

Punnett Squares Notes: Punnett squares: are special charts that are used to show the possible gene combinations in a cross between two organisms. Reginald C. Punnett, an English geneticist, developed the chart

Punnett Squares Notes: Phenotype: is the physical appearance, the visible characteristic. Genotype: is the actual gene makeup.   

Punnett Squares The Chart On top: The Female Portion On this side: The Male Portion

Punnett Squares A cross between guinea pigs. The female guinea pig has black hair (BB) and crosses with a white hair male (bb). What will the F1 (Filial) generation look like? What is the expressed phenotype? What is the genotype?

Punnett Squares What would the phenotype and genotype be if a female white hair guinea pig (bb) and a black hair guinea pig (Bb)? What would they be if the male were a purebred?

Punnett Squares Using the Punnett Square, correctly cross a heterozygous blue eyed person with a homozygous brown eyed  person. (E=blue eyes, e=brown eyes) 

Punnett Squares Use a Punnett square to predict the genotypic and phenotypic outcome (offspring) of a cross between two heterozygous/hybrid tall (Tt) pea plants

Punnett Squares In pea plants, yellow peas are dominant over green peas. Use a Punnett square to predict the phenotypic and genotypic outcome (offspring) of a cross between a plant heterozygous/hybrid for yellow (Yy) peas and a plant homozygous/purebred for green (yy) peas.

Punnett Squares In pea plants, yellow peas are dominant over green peas. Use a Punnett square to predict the phenotypic and genotypic outcome (offspring) of a cross between two plants heterozygous for yellow peas.

Punnett Squares In pea plants, round peas are dominant over wrinkled peas. Use a Punnett square to predict the phenotypic and genotypic outcome (offspring) of a cross between a plant homozygous for round peas (RR) and a plant homozygous for wrinkled peas (rr).

Punnett Squares In pea plants, round peas are dominant over wrinkled peas. Use a Punnett square to predict the phenotypic and genotypic outcome (offspring) of a cross between two plants heterozygous for round peas.

Punnett Squares In dogs, there is an hereditary deafness caused by a recessive gene, “d.” A kennel owner has a male dog that she wants to use for breeding purposes if possible. The dog can hear, so the owner knows his genotype is either DD or Dd. If the dog’s genotype is Dd, the owner does not wish to use him for breeding so that the deafness gene will not be passed on. This can be tested by breeding the dog to a deaf female (dd). Draw the Punnett squares to illustrate these two possible crosses. In each case, what percentage/how many of the offspring would be expected to be hearing? deaf? How could you tell the genotype of this male dog? Also, using Punnett square(s), show how two hearing dogs could produce deaf offspring.

Punnett Squares In humans, brown eyes (B) are dominant over blue (b). A brown-eyed man marries a blue-eyed woman and they have three children, two of whom are brown-eyed and one of whom is blue-eyed. Draw the Punnett square that illustrates this marriage. What is the man’s genotype? What are the genotypes of the children?

Punnett Squares RY Ry rY ry RRYY Punnett square for a Dihybrid Cross In the pea plant, two characteristics for the peas, shape and color, will be used to demonstrate an example of a dihybrid cross in a punnett square. R is the dominant gene for roundness for shape, with lower-case r to stand for the recessive wrinkled shape. Y stands for the dominant yellow pea, and lower-case y stands for the recessive green color. By using a punnett square (the gametes are RY, Ry, rY, and ry): RY Ry rY ry RRYY

Punnett Squares Di-hybrid Crosses: You have to look at the options if it is Rr and Tt the parent can pass on RT, Rt, rT, rt.

The result is a 9:3:3:1 phenotypic ratio, as shown by the colors, where yellow represents a round yellow (both dominant genes) phenotype, green representing a round green phenotype, orange representing a wrinkled yellow phenotype, and blue representing a wrinkled green phenotype (both recessive genes).

Punnett Squares Monohybrid, Dihybrid, Trihybrid Cross Practice Page