Predicting genetic outcomes PUNNETT SQUARES Predicting genetic outcomes

Gregor Mendel discovered the principles of inheritance studying pea plants. The pea plants that he used produced peas with four characteristics: Shape of peas = Round vs wrinkled Color of peas = Yellow vs green Color of the pod = Green vs yellow Height = Tall vs short

Gametes have only one allele of each gene Gametes are haploid

The purpose of a punnett square is to show all the possible combinations of genetic information for a particular trait in a cross. A monohybrid cross is one which shows the results for one trait.

Capital letters are used to represent dominant alleles, while the lower case of the same letters are used for the recessive allele. In a monohybrid cross, each parent has two alleles for what ever trait is being investigated.

First you draw four boxes

Then you put the possible gametes produced by one parent on the top and possible alleles of the other parent on the side

Then you fill in the boxes by bringing the alleles down and across

Each square represents 25% so there is a 25% probability of getting TT, 50% Tt and 25% tt

TEST CROSS A test cross is done to determine homozygous vs heterozygous in an organism exhibiting a dominant phenotype. You cross the unknown genotype dominant trait with a recessive trait and study the outcome.

TEST CROSS Example, you have a tall pea plant but you don’t know if it’d homozygous TT or heterozygous Tt. Cross it with a short tt plant. If the unknown plant is TT, all of the offspring will be tall Tt. If the unknown plant is Tt, 50%of the offspring will be tall Tt and 50% will be short.

Mono Hybrid cross problems Cross a heterozygous Type A male with a homozygous B female. Give possible blood types