Punnett Squares HELP!!?

i need some help i am usually really good at biology but one thing i do not understan are these punnett squares.THANKS! :)





Refer to the following information to answer Questions 4 through 7.A horticulturalist wants to produce geraniums with specific characteristics. She knows that the trait of red flowers is governed by the allele R (RR and Rr) and the trait of white flowers is governed by the allele r (rr).





1. The horticulturalist plans to cross a geranium that is true-breeding for red flowers with a geranium that is true-breeding for white flowers. What would this Punnett square look like.





2. The horticulturalist crosses two geraniums from the F1 generation. Look at the Punnett square to see this cross. What ratio of red- to white-flowering plants would you expect to see in the phenotypes of the F2 generation?


A. 1 red: 3 white


B. 3 red: 1 white


C. 2 red: 2 white


D. all red


the punnett square looks like this


R r





R RR Rr





r Rr rr

Punnett Squares HELP!!?
For the first question, you know that the red flowered plant must be RR since it is "true-breeding". True breeding ALWAYS means homozygous. Since the white flowered plant has to be rr (white is recessive to red), the punnett square will have 2 R's on the top and two r's on the side. All four boxes inside will have Rr in them, so all of the offspring will be red flowered, but they will all be heterozygous.





The answer to the second question is B. The Punnett square you have diagramed for this cross is correct. Any of the offspring with R_ will have red flowers and only the rr will have white flowers...





Hope this helps.
Reply:1. This is hard to describe in words alone, but I'll try.


Make a square with 4 boxes inside it.The red flower, if true breeding, will have RR genes (its genotype). The white will have rr genes


On the square, put one R above the first box and one over the second box. (on top of the box)


Then on the left side, put one r beside the first box, and then one beside the second one down.


In each box, combine the letters that are directly above the box with the letters to the side each box.


Each box will the contain 1 R and 1 r giving you 4 boxes with Rr, which means they will all be red.





2. There will be 3 red to 1 white. 1 of the red ones has RR, 2 have Rr, and the white one has rr. As long as there is at least one R the flower will be red. To be white, 2 r's (rr) are required.





Hope this helped!