Download GENETIC TERMINOLOGY

GENETIC TERMINOLOGY
A large amount of the understanding about inheritance patterns was discovered before it was
discovered that genes are the recipes for making ______________. As a result, the terminology used to
describe inheritance patterns does not reflect this. In fact, it actually confuses the issue. That is why we have
carefully avoided it up to now. It is important that you encounter these terms. You never know when you’ll
need them at a party, another biology course, etc, and I wouldn’t want you to look foolish.
To this end, I have assembled some of the commonly used terms here. Your job is to scour your
memory and give an example of a trait that we have examined for each type of inheritance that is listed here.
Please give an explanation of why you feel they match
Dominant and recessive expression is not necessarily all or nothing. Dominant does not imply that
a trait is stronger, better, or more prominent in the population. To say that a dominant allele
prevents the expression of a recessive allele is most often untrue. Both dominant and recessive
genes are independently expressed at the same time, meaning there are 2 different DNA codes for 2
different PROTEINS. Dominance does not mean that the dominant protein is the only protein being
produced. Generally the recessive gene is transcribed into mRNA just as the dominant gene and
depending on the gene the recessive gene may also be translated into a polypeptide. The function
of the recessive polypeptide may be used for a different product or may lose its ability to catalyze a
reaction or may only be functional in certain environmental conditions, such as the case in Sickle
Cell Anemia. The alternative Hemoglobin protein does in fact carry oxygen but only when there is a
high concentration of O2 in the blood.
1. Polygenic Inheritance This is probably one of the most common modes of inheritance around. It is a
situation where more than one gene influences one phenotypic characteristic.
2. Multiple Alleles: Many genetics problems present traits that only have two variations. In fact this is most
often not true. There are usually more than two versions of each gene and therefore more than two
versions of ____________. Hence the term coined here.
3. Dominant and Recessive traits (also known as simple Dominance). In this type of pattern the presence of
one “dominant” allele produces sufficient protein so that it is noticed as the phenotype. Recessive proteins
only are noticed phenotypically when a person is homozygous for that allele. Dominant traits are indicated
by a capital letter, recessive by a lower case letter.
4. Co-Dominance is a situation where both alleles produce proteins that are noticed (either physically or
functionally) in the phenotype.
5. Incomplete Dominance: An inheritance pattern in which the proteins blend in heterozygotes to produce an
intermediate form.