Q&A for How to Make a Punnett Square

Generally your teacher will use common examples that you know or have from the Mendelian pea experiment. Also, if the letter is capitalized it is the dominant allele - recessive allele is the lower case letter. Often the letter for the trait corresponds to the dominant allele - like tall is dominant to short so the teacher will use the letters T = tall and t = short.

Because in the specific example used, one parent has two recessive alleles and the other parent has one dominant allele and one recessive allele. If you look at the resulting square, it's clear why the possible outcomes are 50/50: there's a 50% chance that the offspring will inherit recessive alleles from both the father and the mother. If both parents had one dominant allele and one recessive allele, then there would only be one possible recessive-recessive combination, and the chance of yellow in the offspring would be only 25%.

The dominant allele (for example, B) is the one that, in a normal cross, will show up in the phenotype if either one or two of itself are present. So, if Bb and BB produce the same phenotype, you know that B is dominant because both 1 and 2 B's produce the same result The recessive allele (for example, b) is the one that needs two of itself in order to be expressed in the phenotype. So, if b is recessive and B is dominant, only bb will show the recessive allele in the phenotype.

Draw a square divided into four parts. Put each of the parent's genotype above each small box at the top of the big square, and the other parents' on the left side (up to down) next to each small box. The recessive allele, or the lowercase letter, comes after the uppercase one.

Dominate will have at least one or more capital letters in the box; a recessive will have two lower case letters in the box and that will be the only time it is double recessive allele.

The hybrid is always a mix of the capital and lowercase letters (you can use any letters). For example: F is white colored fur. F is dominant and black colored fur (f), is recessive. A purebred will always be either FF or ff. If a white colored fur animal and a black colored fur animal breed, this creates a hybrid, which is Ff, because one gene goes to the offspring from each parent.

When there are more alleles that affect the trait, more boxes are tracked. I heard eye color has six alleles that affect it. Also, your teacher might had put the parents in the top box (not above it) and in the left most box (not before it).

If you were to cross over the two together, you'd get a 100% phenotype of that dominant trait.

The phenotype is the physical description, the genotype is what the alleles are.

You can't because the punnet square doesn't give you that kind of information.

X and Y chromosomes are used if you want to determine the probability of having offspring of a certain gender or the probability of inheriting a gene which is X-linked. FF and Ff are used when you are working out the inheritance of autosomal genes (genes that are not linked to X or Y chromosomes).

A monohybrid cross uses a 2x2 Punnett square. There are 4 possible outcomes so there are 4 squares.

Generally, the dominant allele is marked with a capital letter, while the recessive one is marked with a lowercase letter. Recessive traits are rarer, since they appear only when there is no dominant allele. AA = dominant phenotype. Aa = dominant phenotype. aa = recessive phenotype.