Traits and Inheritance Part II

The mathematical chance that something will happen is known as probability.

Finding the probability of certain genotypes for offspring is like predicting the results of a coin toss. To have white flowers, a pea plant must receive a p allele from each parent.

Each offspring of a Pp Pp cross has a 50%

chance of receiving either allele from either parent. So, the probability of inheriting two p alleles is 1/2 1/2. This equals 1/4, or 25%.

As scientists learned more about heredity, they found exceptions to Mendel’s principles.

INCOMPLETE DOMINANCE

Sometimes, one trait isn’t completely dominant over another. These traits do not blend together, but each allele has an influence on the traits of offspring. This is called incomplete dominance. For example, the offspring of a true-breeding red snapdragon and a true-breeding white snapdragon are all pink. This is because both alleles for the gene influence color

ONE GENE, MANY TRAITS

In Mendel’s studies, one gene controlled one trait. However, some genes affect more than one trait. For example, some tigers have white fur instead of orange. These white tigers also have blue eyes. This is because the gene that controls fur color also affects eye color.

MANY GENES, ONE TRAIT

Some traits, such as the color of your skin, hair, and eyes, are the result of several genes acting together. In humans, different combinations of many alleles can result in a variety of heights.

THE IMPORTANCE OF ENVIRONMENT

Genes are not the only things that can affect an organism’s traits. Traits are also affected by factors in the environment. For example, human height is affected not only by genes. Height is also influenced by nutrition. An individual who has plenty of food to eat may be taller than one who does not.