# The drawing of genetic crosses

I'm preparing myself for the GRE. The quantitative stuff has all been going well. I'm aiming for a geology grad scheme. In the event of having to take subject specific tests, I'm teaching myself a few "out there" things in science.

I'm going through biology and looking at genetics for the first time since high school(!)

I just had a question here really to do with genetic crosses. I've been looking at Mendel and the experiments he carried out. One specifically looking at short pea plants. I'm looking at an example where all F1 plants are tall (F1 being the generation of plants). In the example the F2 generation are created in selfing the F1 plants.

Now, I've got my head around the science involved, but I just basically wondered if any biologists here could show me how to make a genetic cross of F2 in order that I could show the genotypes and phenotypes of the offspring.

This isn't necessary but I feel as though it would help my understanding.

At the moment I'm drawing a two by two grid. I suppose I need to fill it with the appropriate alleles?

Thanks.

• One of my most valuable sources has been this: indiana.edu/~p1013447/dictionary/mendel.htm – I come from a land down under Jun 30 '16 at 11:03
• The diagram that you are looking for is called a punnet square. – C_Z_ Jun 30 '16 at 16:13
• What's a GRE? (I have Googled it now, but I wanted to make you aware that's not a widely known term outside the US - you might want to explain it). – arboviral Jun 29 '17 at 11:37
• (I also added the 'homework' tag. Please don't consider this as a negative - in my opinion this is an example of a 'good' homework tag!) – arboviral Jun 29 '17 at 11:38

## 1 Answer

The cross you're studying is Mendel's monohybrid cross. Which looks something like this.

Now here, the genotype of F1 gen plants is Tt.

To draw this cross, proceed exactly like you decided. Draw the 2/2 grid and cross the alleles Tt x Tt

Your cross should look like this (ignore the plant drawings):

(Source: classes.midlandstech.com)