Review the background information below if you have trouble understanding any of the steps that follow.
For example, call the dominant gene for black fur “F”, and the recessive gene for yellow fur “f”. If you don’t know which gene is dominant, use different letters for the two alleles.
“Heterozygous” means it has two different alleles (Ff). [1] X Research source “Homozygous dominant” means it has two copies of the dominant allele (FF). “Homozygous recessive” means it has two copies of the recessive allele (ff). Any parent that shows the recessive trait (has yellow fur) belongs to this category.
For example, the female bear is heterozygous for fur color (Ff). Write an F to the left of the first row, and an f to the left of the second row.
For example, the male bear is homozygous recessive (ff). Write an f above each of the two columns.
In our example, the top left box inherits F from the mother and f from the father, to make Ff. The top right box inherits an F from the mother and f from the father, to make Ff. The bottom left box inherits an f from both parents, to make ff. The bottom right box inherits an f from both parents, to make ff.
In our example, we have two boxes with Ff (heterozygous). 25% + 25% = 50%, so each offspring has a 50% chance of inheriting the Ff allele combination. The other two boxes are each ff (homozygous recessive). Each child has a 50% chance of inheriting ff genes.
In this example, there are two squares with at least one F, so each offspring has a 50% chance to have black fur. There are two squares with ff, so each offspring has a 50% chance to have yellow fur. Read the problem carefully for more information about the phenotype. Many genes are more complex than this example. For example, a flower species might be red when it has the RR alleles, white when it has rr, or pink when it has Rr. In cases like this, the dominant allele is then referred to as an incomplete dominant allele. [4] X Research source
An organism with two copies of the same allele is homozygous for that gene. [5] X Research source An organism with two different alleles is heterozygous for that gene.
An organism with one dominant allele and one recessive allele is heterozygous dominant. These organism are also called carriers of the recessive allele, since they have the allele but don’t show the trait. [6] X Research source An organism with two dominant alleles is homozygous dominant. An organism with two recessive alleles is homozygous recessive. Two alleles of the same gene that can combine to make three different colors are called incomplete dominants. An example of this are cream-dilute horses, where cc horses are red, Cc horses are a shade of gold, and CC horses are a light shade of cream.
Someone running a breeding project (usually developing new plant strains) wants to know which breeding pair gives the best chance at good results, or whether a certain breeding pair is worth the effort. Someone with a serious genetic disorder, or a carrier of an allele for a genetic disorder, wants to know the possibility that he’ll pass it on to his children.
