When an allele is represented by a capital letter, it is said to be dominant, and will always be expressed when coupled with another dominant allele. Recessive genes, which are represented by a lowercase letter, are expressed only when an individual is pure and has two copies of the allele.
In kittens, the gene for pointy ears is dominant and the gene for floppy ears is recessive. Kittens will express the pointy ear trait if the kitten is pure for dominant gene or has a hybrid of alleles. In order for floppy ears to be expressed on a kitten, the kitten must be pure for the recessive gene.
Punnett Squares are charts used to predict the odds of specific gene combinations in offspring. Below is a Punnett Square of a cross between two heterozygous parents.
The genotypic ratio of this Punnett Square is best expressed as


The genotypic ratio is the pattern of offspring distribution based on genotype. In this Punnett Square, we have one instance of PP, two instances of Pp, and one instance of pp. Therefore, the genotypic ratio is 1:2:1.

Visit our website for other GED topics now!