Probability and Punnett Probability and Punnett SquaresSquares

10.2 con’t.10.2 con’t.

Punnett squaresPunnett squares are used to are used to calculate the probabilities of genetic calculate the probabilities of genetic outcomes if the genetic makeup of outcomes if the genetic makeup of the parents is known.the parents is known.

Genotype Genotype is the genetic makeup or is the genetic makeup or the combination of alleles an the combination of alleles an individual has. individual has. – Ex: PP, Pp, pp, Bb, or bbEx: PP, Pp, pp, Bb, or bb

PhenotypePhenotype is an observable trait of is an observable trait of an individual.an individual.– Ex: purple, white, brown or blue…Ex: purple, white, brown or blue…

Testcross are used to determine the Testcross are used to determine the unknown genotype of an individual unknown genotype of an individual with a dominate phenotype.with a dominate phenotype.

A purple pea flower could have a A purple pea flower could have a genotype PP or Pp. Crossing the genotype PP or Pp. Crossing the plant with a homozygous recessive plant with a homozygous recessive plant and observing the offspring will plant and observing the offspring will identify the unknown genotype of the identify the unknown genotype of the purple pea. purple pea.

If If the unknown is PP, and a the unknown is PP, and a testcross is done with a white testcross is done with a white

flower (pp) then the offspring will all flower (pp) then the offspring will all be purple (Pp).be purple (Pp).

PP PP

pp PpPp PpPp

pp PpPp PpPp

If If the unknown is Pp, and a testcross is the unknown is Pp, and a testcross is done with a white flower (pp) then the done with a white flower (pp) then the

offspring will be 50% purple (Pp) and 50% offspring will be 50% purple (Pp) and 50% white (pp).white (pp).

PP pp

pp PpPp pppp

pp PpPp pppp

Mendel studied 7 traits of pea plants Mendel studied 7 traits of pea plants and determined what was dominate and determined what was dominate and recessive. See fig 10.4 p209.and recessive. See fig 10.4 p209.

Dihybrid crossDihybrid cross predicts the predicts the probability of offspring with two probability of offspring with two traits.traits.

Through dihybrid crosses, Mendel Through dihybrid crosses, Mendel discoved that traits randomly mix.discoved that traits randomly mix.– Principle of independent assortment.Principle of independent assortment.

Ex: Purple flowers could be on tall or Ex: Purple flowers could be on tall or short plants. Or yellow seeds could short plants. Or yellow seeds could be wrinkled or smooth. be wrinkled or smooth. – The traits do not pass onto the offspring The traits do not pass onto the offspring

in the same combination as in the in the same combination as in the parents.parents.

..

Ex. Tall Purple X short whiteEx. Tall Purple X short white(TTPP) X (ttpp)(TTPP) X (ttpp)

TPTP TPTP TPTP TPTP

tptp TtPpTtPp TtPpTtPp TtPpTtPp TtPpTtPp

tptp TtPpTtPp TtPpTtPp TtPpTtPp TtPpTtPp

tptp TtPpTtPp TtPpTtPp TtPpTtPp TtPpTtPp

tptp TtPpTtPp TtPpTtPp TtPpTtPp TtPpTtPp

What is the outcome of the F1 genetation?

Ex. Tall Purple X short whiteEx. Tall Purple X short white(TTPP) X (ttpp)(TTPP) X (ttpp)

TPTP TPTP TPTP TPTP

tptp TtPpTtPp TtPpTtPp TtPpTtPp TtPpTtPp

tptp TtPpTtPp TtPpTtPp TtPpTtPp TtPpTtPp

tptp TtPpTtPp TtPpTtPp TtPpTtPp TtPpTtPp

tptp TtPpTtPp TtPpTtPp TtPpTtPp TtPpTtPp

F1’s are all heterozygous, tall purple pea plants

If you crossed the F1’s, what would If you crossed the F1’s, what would be the outcome of the F2’s ?be the outcome of the F2’s ?

TtPp X TtPp ?TtPp X TtPp ? You must first figure out the possible You must first figure out the possible

combinations of alleles that the combinations of alleles that the parents can give to the offspring. parents can give to the offspring. Remember that only one allele from Remember that only one allele from each trait is passed on.each trait is passed on.

???? Do you have them???????? Do you have them????

TP, Tp, tP and tpTP, Tp, tP and tp Now set up the dihybrid cross Now set up the dihybrid cross

Punnett square.Punnett square.

Complete the cross and find the Complete the cross and find the genotypic and phenotypic results.genotypic and phenotypic results.

TPTP TpTp tPtP tptp

TPTP

TpTp

tPtP

tptp