Punnett Square Basics | Mendelian Genetic Crosses

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This is a simple overview of monohybrid genetic crosses using punnett squares and Mendelian genetics.

Punnett squares measure the probability or likelihood of a genetic outcome based on a specific genetic cross. It doesn’t tell you what will be, only what could be.

For the simplest of punnett squares you’ll cross two genotypes. These parent genotypes will be for the same gene, but may or may not contain different alleles. Let’s look at an example of a genetic cross for eye color, green eyes being dominant and blue eyes being recessive. Let’s use Gg for the maternal genotype and gg for the paternal. So this is our cross, the mother has green eyes and the father has blue eyes and we want to see the probability that their offspring will have either green or blue eyes.

For this cross we will draw a square split into four quarters, like a simple four panel window. This is the punnett square. One of the parental genotypes will go on top, and the other will go on the side. It doesn’t matter which genotype goes where and the order of the letters doesn’t matter, however, we conventionally write the dominant allele first.

So your setup should look like this.

Then you simply carry the letters through to their respective quadrants and match them up, like so. Each quadrant represents a 25% chance that that genotype will result. So in this case we have only two possible genotypes, Gg and gg. And each genotype has 50% chance of showing up in the offspring. Similarly, you will have two possible phenotypes, Green eyes and Blue eyes, with a 50% chance of each.

Let’s look at another example. Let’s cross two genes that are heterzygous for eye color. Gg X Gg. These colors are just for illustration purposes. We again draw our punnett square and put one gene on top and the other down the side, carry the letters through to their respective quadrants, and analyze the results. This cross results in a 1:2:1 genotype ratio, with 25% Homozygous Dominant GG, 50% Heterozygous Gg, and 25% Homozygous Recessive gg. The phenotypic ratio would be a 3:1 ratio with 75% green eyes and 25% Blue eyes.

Hopefully that helps you understand simple punnett squares. Genetic crosses can be much more complicated and I will make some videos in the future explaining how to tackle those. If you have any questions from this video, throw them in the comments, and don’t forget to like and subscribe. Thanks for watching. I’ll catch you next time.

[josh_oshea]

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[detroithd]

100% the best channel for study, gets straight to the point, no bullshit. Better than crash course

[slaybelle]

just remember that each of those squares are equivalent to 25%!

[LOC]

This video really woke me up I was feeling really tired but then my teacher assigned this to google classroom. I watched it all the way through and took lots of notes, thanks for the lesson 2 minute classroom

[jersfnbr]

This video is great it gets directly to the point, with no bs. Learned more from this than I did in an hour of biology, lowkey saved my grade

[vlogwitheme]

i had to sit in class trying to understand what the teacher was saying abt punnet squares for 2 weeks and u teached me it in 2 minutes!!

[adoredivines]

This actually helped me so much, considering I have a test coming up in a few days 😭 Thank you! Best channel for studying

[hbazikyan]

Thank you for the video. My son was having a hard time understanding the Punnet square so I started looking for a video and came across your video. I learned and then explained to my son how to make Punnet square. Short and precise.

[macncheese]

I don’t know what I would’ve done without this video it was explained way better than my teachers

[anthonykennedy]

thank you for getting to the point really fast, about to take a test and all of the videos are 30 min long, yours on the other hand got right to the point, thank you!

[oo-]

Thank you for this! I’m studying for a test coming up tomorrow and this helped me understand how the Punnett square works!

[Arabiangigachad]

Short, simple, easy to understand, and re-playable. Great vid bro

[icecreamjunkie]

Thank you so much for this. I'm learning about this for biology right now and was a little stumped. Makes way more sense now. Going to watch some more complex examples so I can truly master it!

[lazerleagend]

This was really confusing for me at first cus I couldn't get the difference in GG, Gg. but you helped me alot to learn it and I bot this video from my teacher. your a big help thank you.

[XxMidnightxXDark]

Y’all, this actually rlly worked- I rlly recommend- my grades are horrible for bio/science, but I assure you, this actually helped so much

[oplinx]

I was stressed out because i am currently sick (with strep throat) and my teacher announced on Google Classroom that we have a test on Punnett Squares on Friday, so i decided to watch a video about them and this was the first result. I copied down the example of the Punnet Square and did the worksheet she posted and this helped me so much! The arrows were definitely helpful in figuring out where the genotypes go! Thank you again! (Also she isnt the best teacher so i didnt really understand this even though shes been teaching it for a week! You helped me understand it in 2 minutes!)

[abdullaalromaihi]

Thank you so much for this video! I haven't been listening at all in clas lol and my teacher just posted an assignment about this. Great video, it helped me a lot.

[serenasworld]

I never thought I'd understand how to do these!! thank you so much :))

[Jukebox]

thank you so much for this video it really helped me out a lot with science class lol.

[Back.shts]

Thank you so much, this helped me a lot. Have a quiz on this next period and I feel fully prepared after watching this.