Download Background Information About Traits

Background Information About Traits
Genes control traits: that’s how traits are inherited. (from Britanica online)
How does it happen that children of the same parents may have different inherited traits?
The explanation is, first, that each parent carries two genes for every task but gives each child
only one gene of every pair. For example, suppose the father's two eye-color genes are
different—one is a brown-eye gene, the other a blue-eye gene. One child, then, might get the
father's brown-eye gene, and another might get the blue-eye gene. In the same way a parent
might carry a red-hair gene and a blond-hair gene, a curly-hair gene and a straight-hair gene, and
give a child one or the other.
What happens when a child gets a different gene for the same job from each parent—for
instance, a brown-eye gene from the father and a blue-eye gene from the mother? The answer
was provided in part by Mendel. He discovered that certain factors in determining traits are
dominant, or stronger, and others are recessive, or weaker. He did not know that these factors
were genes, but he did understand the basic principle of how they worked.
When two genes that control the same trait are different, the dominant gene wins out. In
the case of eye color, the brown-eye gene is dominant and will take over the job of coloring the
baby's eyes. The recessive blue-eye gene will not show its effects. Only if a child receives two
blue-eye genes, one from each parent, will the child have blue eyes. People with brown eyes
therefore may have two brown-eye genes or they may have one brown-eye gene and one blueeye gene. That is why brown-eyed parents may produce a blue-eyed baby. But if both parents are
blue-eyed, this indicates that they have no brown-eye gene to pass along. They will produce only
blue-eyed children.
There are a great many other traits in which dominant and recessive genes are involved.
In hair color, black or brown genes are dominant over red and blond genes while, by itself, the
red gene dominates the blond gene. Long-nose genes tend to dominate short-nose genes, and so
on.
The more differences there are in the parents' genes, the more possible it is for them to
pass on different combinations of genes. Therefore, their children may differ greatly from one
another in various hereditary traits.
In the second part of this lesson students will look at how the same gene might be
expressed differently in two similar species and how that difference in expression will affect
where those two species will survive.