In the 1800s, an Austrian Monk named Gregor Mendel first began performing breeding experiments using garden-variety pea plants. His studies earned him the nickname the father of genetics and his findings laid important groundwork for modern rules of inheritance patterns.
Mendel's work provided basic laws establishing the rules for inheritance patterns. Understanding these patterns requires grasping the concepts of genotypes and phenotypes. These terms might sound unfamiliar, but there is a simple explanation for each.
A phenotype is merely how a gene is expressed. For instance, a dimpled chin is an example of a trait that is governed by genetics. Your phenotype is determined by whether or not you have a dimple in your chin. If you have a dimpled chin, you express the trait. By the way, this means the trait is dominant. A recessive trait, no dimpled chin for instance, is one in which the trait is hidden; hence, the term recessive.
A genotype, on the other hand, is the actual hereditary information of an individual. This means that a genotype represents both copies of the alleles one inherits for a particular trait. Remember, a person inherits two copies of a particular gene -- one from each parent.
The rules of dominance in inheritance patterns are relatively clear-cut. An individual who inherits two recessive alleles will always mask or hide the trait. This individual would also be considered homozygous recessive.
Recessive alleles are typically indicated with lowercase letters. So, if we say the trait for dimpled chin is represented by a lowercase letter d, then an individual who inherits two recessive alleles, one that came from each parent, will have the dd genotype. Again, someone with this genotype is said to be a recessive homozygote.
Consequently, if an individual inherits two dominant alleles, the trait will always be expressed. This is also known as homozygous dominant. Dominant alleles are written with, you guessed it, capital letters; therefore, someone with two dominant alleles, DD, for the dimpled chin trait will surely have a dimpled chin.
Then what if a person inherits one dominant allele and one recessive allele -- the genotype of Dd? This would mean they are heterozygous; therefore, they will always express the trait. The reasoning behind this is that dominant alleles are just that -- dominant. Even if inherited alongside a recessive allele, a dominant trait will inevitably be expressed.
Another fascinating feature of recessive traits is that they hold more significance than merely being hidden. In certain cases, inheriting two copies of a recessive allele may indicate that a person will have a particular genetic disease. A few common recessive inherited disorders are Sickle Cell Anemia, Tay Sachs, and Cystic Fibrosis.
These recessive diseases are examples of autosomal disorders, which are disorders linked to the 22 chromosome pairs which do not determine gender. Also curious is that there are dominant inherited disorders which are very lethal and sex-linked disorders that are related to genetic mutations on the X and Y chromosomes.
Blood type is a special type of inherited trait that is governed by multiple alleles, or gene variants. Most often referred to as the ABO blood group, these three alleles, A, B, and O, can produce four phenotypes from six genotypes. Of the three possible alleles, A and B are always dominant to O.
Furthermore, A and B are codominant meaning if inherited together, both will be expressed. As in any inherited trait, only one allele will come from each parent. The possible combinations are AO, AA, BO, BB, OO, and AB. The phenotypes that result are type A blood for AO and AA genotypes, type B blood for BO and BB genotypes, type O blood for the OO genotype, and type AB blood for the AB genotype. - 15437
Mendel's work provided basic laws establishing the rules for inheritance patterns. Understanding these patterns requires grasping the concepts of genotypes and phenotypes. These terms might sound unfamiliar, but there is a simple explanation for each.
A phenotype is merely how a gene is expressed. For instance, a dimpled chin is an example of a trait that is governed by genetics. Your phenotype is determined by whether or not you have a dimple in your chin. If you have a dimpled chin, you express the trait. By the way, this means the trait is dominant. A recessive trait, no dimpled chin for instance, is one in which the trait is hidden; hence, the term recessive.
A genotype, on the other hand, is the actual hereditary information of an individual. This means that a genotype represents both copies of the alleles one inherits for a particular trait. Remember, a person inherits two copies of a particular gene -- one from each parent.
The rules of dominance in inheritance patterns are relatively clear-cut. An individual who inherits two recessive alleles will always mask or hide the trait. This individual would also be considered homozygous recessive.
Recessive alleles are typically indicated with lowercase letters. So, if we say the trait for dimpled chin is represented by a lowercase letter d, then an individual who inherits two recessive alleles, one that came from each parent, will have the dd genotype. Again, someone with this genotype is said to be a recessive homozygote.
Consequently, if an individual inherits two dominant alleles, the trait will always be expressed. This is also known as homozygous dominant. Dominant alleles are written with, you guessed it, capital letters; therefore, someone with two dominant alleles, DD, for the dimpled chin trait will surely have a dimpled chin.
Then what if a person inherits one dominant allele and one recessive allele -- the genotype of Dd? This would mean they are heterozygous; therefore, they will always express the trait. The reasoning behind this is that dominant alleles are just that -- dominant. Even if inherited alongside a recessive allele, a dominant trait will inevitably be expressed.
Another fascinating feature of recessive traits is that they hold more significance than merely being hidden. In certain cases, inheriting two copies of a recessive allele may indicate that a person will have a particular genetic disease. A few common recessive inherited disorders are Sickle Cell Anemia, Tay Sachs, and Cystic Fibrosis.
These recessive diseases are examples of autosomal disorders, which are disorders linked to the 22 chromosome pairs which do not determine gender. Also curious is that there are dominant inherited disorders which are very lethal and sex-linked disorders that are related to genetic mutations on the X and Y chromosomes.
Blood type is a special type of inherited trait that is governed by multiple alleles, or gene variants. Most often referred to as the ABO blood group, these three alleles, A, B, and O, can produce four phenotypes from six genotypes. Of the three possible alleles, A and B are always dominant to O.
Furthermore, A and B are codominant meaning if inherited together, both will be expressed. As in any inherited trait, only one allele will come from each parent. The possible combinations are AO, AA, BO, BB, OO, and AB. The phenotypes that result are type A blood for AO and AA genotypes, type B blood for BO and BB genotypes, type O blood for the OO genotype, and type AB blood for the AB genotype. - 15437
About the Author:
RJ Sullivan manages several successful home-based businesses and is a distinguished editor and writer. Ms. Sullivan also writes for In the Gno, a blog devoted to demystifying the science of genetics in an interesting and easy-to-understand manner. Visit her blog to learn more about mendelian genetics or blood types.
