What do punnett squares represent

The yellow pea phenotype has a genotype of AA. The green pea phenotype has a genotype of aa. When Mendel looked at the results of this mating, he saw that all of the offspring had yellow seeds. How did this happen? If one of the parent plants had green peas, why didn't a single one of the children plants have green peas? We can answer these questions and understand what's happening to the alleles in this crossing with the help of a Punnet Square. Next, fill in each cell with two alleles, one from the parent along the top and one from the parent along the side.

The letters in the middle show you all possible combinations of alleles that can happen from mating these two genotypes. In this case, all offspring have the same genotype and phenotype. These offspring are said to be heterozygous, meaning that they have two different alleles for pea color. Despite the fact that both alleles are present in the offspring, the traits did not blend together to result in yellowish-green peas.

Instead, only one phenotype was visible and all peas were yellow. Because of this, the yellow pea phenotype is said to be dominant, meaning that it is visible in the heterozygous individual.

For the second generation, Mendel mated the heterozygous offspring from the first generation together. Why did this happen? How was it possible for some of the offspring to have green seeds when both of the parent plants had yellow seeds? Let's once again use a Punnet square to answer these questions and understand what's happening to the alleles in this crossing. By looking at the Punnett square, we see that there are three possible genotypes that could result from this crossing: AA, Aa, aa.

The genotypes AA and Aa will result in the yellow pea phenotype because A is dominant. Of course, you are worried about whether your children will be healthy and normal. For this example, let us define "A" as being the dominant normal allele and "a" as the recessive abnormal one that is responsible for cystic fibrosis. As carriers, you and your mate are both heterozygous Aa.

This disease only afflicts those who are homozygous recessive aa. If a carrier Aa for such a recessive disease mates with someone who has it aa , the likelihood of their children also inheriting the condition is far greater as shown below. On average, half of the children will be heterozygous Aa and, therefore, carriers. The remaining half will inherit 2 recessive alleles aa and develop the disease.

It is likely that every one of us is a carrier for a large number of recessive alleles. Some of these alleles can cause life-threatening defects if they are inherited from both parents. In addition to cystic fibrosis, albinism, and beta-thalassemia are recessive disorders. Some disorders are caused by dominant alleles for genes. Inheriting just one copy of such a dominant allele will cause the disorder.

Lower case letter. Both capital and lower case letters. In a Punnett Square, the recessive character or allele is represented by Capital letter. Punnett Square is based upon The function of a Punnett Square is Send Your Results Optional. Your Name. To Email. Time is Up! Dominance This tutorial presents Gregor Mendel's law of dominance. The purple-flowered parent, on the other hand, could have either the BB or the Bb genotype. The Punnett square in Figure below shows this cross.

The question marks? This Punnett square shows a cross between a white-flowered pea plant and a purple-flowered pea plant. Can you fill in the missing alleles? What do you need to know about the offspring to complete their genotypes? Can you tell what the genotype of the purple-flowered parent is from the information in the Punnett square? No; you also need to know the genotypes of the offspring in row 2.

What if you found out that two of the four offspring have white flowers? Now you know that the offspring in the second row must have the bb genotype. The other b allele must come from the purple-flowered parent. Therefore, the parent with purple flowers must have the genotype Bb. When you consider more than one characteristic at a time, using a Punnett square is more complicated. This is because many more combinations of alleles are possible.

For example, with two genes each having two alleles, an individual has four alleles, and these four alleles can occur in 16 different combinations. This is illustrated for pea plants in Figure below. In this cross, known as a dihybrid cross , both parents are heterozygous for pod color Gg and pod form Ff. Punnett Square for Two Characteristics.