Probability and Punnett Squares Please take out your snowbaby, science journal and any missing work (graphs)?

PUNNETT SQUARES  Bunny Punnett Square Bunny Punnett Square 5:03 minutes Eye Color Punnett Square 4:00 minutes

PROBABILITY  Probability is the likelihood that an event will occur. What chance does it have of happening?  Punnett squares are a useful tool for predicting what the offspring will look like when mating plants or animals.  Punnett squares only show the probability (chance) of the offspring, NOT exactly what will happen.  Reginald Crundall Punnett, a mathematician, came up with these in 1905, long after Mendel's experiments.

PHENOTYPE AND GENOTYPE  Ph enotype - An organism’s ph ysical appearance or visible traits. What can be seen. (ex: red flowers, or white flowers)  Gen otype - An organisms gen etic makeup or allele combination. What can not be seen. (ex:Aa, AA, aa)  Allele – 2 forms of a gene, 1 from each parent.  Al lele - Al phabet

HETEROZYGOUS AND HOMOZYGOUS  Heterozygous - Also known as a hybrid, is when the allele combination is one of each, one dominant and one recessive. (Aa)  Homozygous- is when the allele combination is the same, both dominant (AA) or both recessive (aa).

G = grey fur g = white fur 3 crosses have a dominant allele (GG, Gg, and Gg) and 1 cross has 2 recessive alleles (gg) so 75% have the chance to have gray fur and 25% have the chance to have white fur.

 Punnett Square Practice Page Punnett Square Practice Page  You can try these at home if you need more practice!  Let’s do some together.

 Let's say that in seals, the gene for the length of the whiskers has two alleles. The dominant allele (W) codes long whiskers & the recessive allele (w) codes for short whiskers.  a) What percentage of offspring would be expected to have short whiskers from the cross of two long-whiskered seals, one that is homozygous dominant and one that is heterozygous ?  b) If one parent seal is pure long-whiskered and the other is short-whiskered, what percent of offspring would have short whiskers?

P-SQUARE PRACTICE QUESTION #1A  A) What percentage of offspring would be expected to have short whiskers from the cross of two long-whiskered seals, one that is homozygous dominant and one that is heterozygous? W w W a) W = allele for long whiskers w = allele for short whiskers homozygous dominant seal = WW w heterozygous seal =Ww ANSWER: 0% WW Ww

P-SQUARE PRACTICE QUESTION #1B  b) If one parent seal is pure long-whiskered and the other is short-whiskered, what percent of offspring would have short whiskers?  ANSWER: 0%.  Again, I suggest starting by defining symbols like so: W = allele for long whiskers w = allele for short whiskers "Pure" is the same as homozygous, so "pure long-whiskered" would be "WW". If you're a seal, the only way to have short whiskers is to have the homozygous recessive genotype, in other words be "ww". So our cross is: WW x ww.W Ww w w

P-SQUARE PRACTICE QUESTION #2  In purple people eaters, one-horn is dominant and no horns is recessive. Draw a Punnet Square showing the cross of a purple people eater that is hybrid for horns with a purple people eater that does not have horns. Use H and h for your alleles. Summarize the genotypes & phenotypes of the possible offspring.

P-SQUARE PRACTICE QUESTION #2  In purple people eaters, one-horn is dominant and no horns is recessive. Draw a Punnet Square showing the cross of a purple people eater that is hybrid for horns with a purple people eater that does not have horns. Use H and h for you alleles. Summarize the genotypes & phenotypes of the possible offspring. What are the alleles for the hybrid parent? Hh What are the alleles for the parent without horns? Both recessive, so hh What are the genotypes? 50% hybrid (Hh), 50% homozygous recessive (hh) What are the phenotypes? 50% have 1 horn and 50% do not. HhHh hhhh Hh hh

 Now it is your turn with some sample problems. Have fun! Use the back of this sheet to answer the questions below. Don’t forget to determine your alleles first and then make your Punnett Square. One unicorn carries heterozygous, straight horned traits, and its mate carries homozygous spiral horned traits. Use a Punnett Square to determine the probability (what percentage) of one of their offspring having a spiral horn. Use any letter you’d like to represent the alleles.

 One Sasquatch carries heterozygous, long-haired traits, and its mate carries homozygous short-haired traits. Use a Punnett Square to determine the genotypes & phenotypes of the possible offspring. Use any letter you’d like for the alleles. Then summarize the phenotypes and genotypes.