Probability and Punnett Squares 10.2 con’t.
Punnett squares are used to calculate the probabilities of genetic outcomes if the genetic makeup of the parents is known.
Genotype is the genetic makeup or the combination of alleles an individual has. • Ex: PP, Pp, pp, Bb, or bb • Phenotype is an observable trait of an individual. • Ex: purple, white, brown or blue…
Testcross are used to determine the unknown genotype of an individual with a dominate phenotype. • A purple pea flower could have a genotype PP or Pp. Crossing the plant with a homozygous recessive plant and observing the offspring will identify the unknown genotype of the purple pea.
If the unknown is PP, and a testcross is done with a white flower (pp) then the offspring will all be purple (Pp).
If the unknown is Pp, and a testcross is done with a white flower (pp) then the offspring will be 50% purple (Pp) and 50% white (pp).
Mendel studied 7 traits of pea plants and determined what was dominate and recessive. See fig 10.4 p209. • Dihybrid cross predicts the probability of offspring with two traits.
Through dihybrid crosses, Mendel discoved that traits randomly mix. • Principle of independent assortment. • Ex: Purple flowers could be on tall or short plants. Or yellow seeds could be wrinkled or smooth. • The traits do not pass onto the offspring in the same combination as in the parents. .
Ex. Tall Purple X short white(TTPP) X (ttpp) What is the outcome of the F1 genetation?
Ex. Tall Purple X short white(TTPP) X (ttpp) F1’s are all heterozygous, tall purple pea plants
If you crossed the F1’s, what would be the outcome of the F2’s ? • TtPp X TtPp ? • You must first figure out the possible combinations of alleles that the parents can give to the offspring. Remember that only one allele from each trait is passed on. • ???? Do you have them????
TP, Tp, tP and tp • Now set up the dihybrid cross Punnett square.