Probability of Inheritance Lesson 2 Mrs. Anna Ward Seventh Grade Science Ridge Road MS

DO NOW!!!! Copy down this diagram in your notes!!!!

Agenda Review from yesterday. What is a Punnett Square? Why do we use them? What can they tell me? How to do a Punnett Square Six Steps to Success Discovery Ed video Think, Pair, & Share Practice

Punnett Square…What are they and why do we use them? A Punnett Square is a chart used to show the possible ways genes from two parents can combine in order to predict possible genotypes of offspring Punnett Squares also help us determine the probability and ratios of these offspring.

Punnett Squares— STEP ONE Identify the Genotypes of Each Parent! In this case: TT and tt

PUNNETT SQUARES STEP TWO DRAW A BOX WITH A CROSS.

Punnett Squares— STEP THREE Add the Genotype information from One parent across the top. Add the Genotype information from the other parent down the side. TT x tt t t

Punnett Squares— STEP FOUR Add the Alleles from One Parent to the Punnett Square. TT x tt T T t t T T

Punnett Squares— STEP FIVE Add the Alleles from the other Parent to the Punnett Square. TT x tt t T t T t t T t T t

Punnett Squares— STEP SIX Calculate the Results The final result of crossing a Pea Plant (TT) with a Pea Plant (tt) is that all the offspring will have the GENOTYPE “Tt”. CFU: If all the genotypes are “Tt” what is the phenotype? (Are they tall or short?)

However, if those two plants are crossed… What Happens??? Remember step one…IDENTIFY THE PARENT GENOTYPES! Tt x Tt

STEP 2 Draw the Box with a cross.

STEP 3 T t Add in the Genotypes of the parents across the top and down the side. Tt x Tt T t

STEP 4 T t Add the alleles from one parent into the Punnett Square Tt x Tt T T t t T t

STEP 5 T t Add the alleles from the other parent into the Punnett Square Tt x Tt T T T T t t T t t t NOTE: When writing genotypes, the DOMINANT allele ALWAYS comes first!!!!!

Step 6—Calculate the Final Results.. When crossing two plants with a Tt genotype we get… One plant with the genotype TT Two plants with the genotype Tt One plant with the genotype tt

Checking for Understanding… What are the phenotypes for the Genotypes of this Punnett Square? One plant with the genotype TT Two plants with the genotype Tt One plant with the genotype tt TALL TALL Short In other words, we get three tall plants for every one short plant.

Discovery Ed Video to help explain…. http://player.discoveryeducation.com/index.cfm?guidAssetId=AB33 E612-2755-4901-8A44-857151E3BB24

Punnett Squares The type of Punnett Squares we are doing are MONOHYBRID CROSSES. Monohybrid Crosses are used to evaluate the potential genotypes of offspring when looking at traits that are determined by a single allele. You will need to know the steps for completing a Monohybrid Cross (or Punnett Square). Glue in the Punnett Square Cheat Sheets into your science notebook.

Now it is time for you to practice… What would the result of crossing a Heterozygous Tall pea plant (Tt) with a homozygous Tall pea plant? What would be the result of crossing a homozygous Short pea plant (tt) with a homozygous Short pea plant (tt)? What would be the result of crossing a heterozygous Tall (Tt) pea plant with a homozygous Short pea plant? What would be the result of crossing a heterozygous tall pea plant with a heterozygous tall pea plant?

Exit Ticket… Which of the following is a heterozygous genotype? Aa BB cc DD What is another name for the type of Punnett Squares we are completing? What would happen if I cross a HOMOZYGOUS DOMINANT Brown Haired Woman (BB) with a HOMOZYGOUS RECESSIVE Blond Haired Man?