thanks for stopping by today we're talking about the basics of punet squares punet 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 punet squares you'll cross two genotypes these parent genotypes will be for the same gene but may or may not contain different alyss let's look at an example of a genetic cross for eye color green eyes being dominant and blue eyes being recessive and we'll use Big G little G for the maternal genotype and little G little G 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'll draw a square split into four quarters like a simple four panel window this is the punet 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 really doesn't matter but we conventionally write the dominant alil first if there is a dominant Al so your setup should look like this then you simply carry the letters through to their respective quadrants and match them up like so all right each quadrant will represent a 25% chance that that genotype will result in The Offspring so in this case we have only two possible genotypes Big G little G and little G little G and each genotype has a 50% chance of showing up in in The Offspring similarly you have two possible phenotypes green eyes and blue eyes with a 50% chance of each let's look at another example uh we'll cross two genes that are heterozygous for eye color in this example so big G little G crossed with big G little G these colors are just for illustration purposes so we again will draw our punet square and put one gene on top and the other down the side and then carry the letters through to the their respective quadrants and analyze the results so this cross results in a 1:2:1 genotype ratio with 25% homozygous dominant or Big G Big G 50% heterozygous or Big G little G and 25% homozygous recessive or little G little G the phenotypic ratio would be a 3:1 ratio with 75% green eyes and 25% blue eyes okay hopefully that helps you understand simple punet squares a little better genetic crosses can be much more complicated and I'll make a video sometime in the future explaining how to tackle those more complicated genetic crosses 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