Question

How do I make and use a Punnett square?

Answer 1

A Punnett Square shows the genotypes two individuals can produce when crossed. To draw a square, write all possible allele* combinations one parent can contribute to its gametes across the top of a box and all possible allele combinations from the other parent down the left side.

Explanation:

Diagrams and online calculator here:
http://scienceprimer.com/punnett-square-calculator

Answer 2

See below:

Explanation:

A Punnett square is a grid diagram that is used to predict the outcome of breeding.

Let's pretend that we have a type of plant that has two alleles for height:

`"T"` which means `"tall"` and is `"dominant"`
`"t"` which means `"short"` and is `"recessive"`

A `"Tt"` tall plant breeds with another `"Tt"` tall plant. What types of offspring can they produce?

We will make a 4-square grid and put the father's alleles on the top, and the mother's alleles on the sides:

Now we will move each letter down on it's column or to the right in it's row.

The red `color(red)"T"` and `color(red)"t"` are from the father and the blue `color(blue)"T"` and `color(blue)"t"` are from the mother.

So the possibilities of their offspring's allele combinations would be in each of the four squares:

`"TT, Tt, Tt, and tt"`

What are the percent chances of each of the allele combinations?

`"TT"`: `1/4` plants or `25%`

`"Tt"`: `2/4` plants or `50%`

`"tt"`: `1/4` plants or `25%`

What are the chances that the offspring will be tall, and what are the chances that they'll be short?

To be tall, they only need one capital `"T"` allele, since `"tall"` is a dominant trait.

`"Tall"`: `3/4` plants or `75%`

`"Short"`: `1/4` plants or `25%`

Now remember that these are just percentages! That doesn't mean that these two parents will definitely produce `4` offspring, `3` tall and `1` short. They're just estimations, so they can be wrong!

Punnett squares can be very complicated, but I hope this has helped you understand the basics! Please let me know if you have more questions - I can just update the answer :)