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.
The work of Gregor Mendel established fundamental rules for patterns of inheritance. The principles of genotypes and phenotypes must first be understood before mastering Mendel's rules. Although unfamiliar, these terms have a simple explanation.
A phenotype is the physical manifestation of a gene. A dimpled or cleft chin is an example of an inherited trait. Your phenotype is established by whether you have a dimple in your chin. In other words, you express the trait if you have a dimpled chin. In addition, this means the trait is dominant. A hidden trait, for example no dimpled chin, is known as recessive.
Conversely, a genotype is the full genetic information of an individual. So this means a genotype represents both of copies of the gene for a particular trait. Remember, everyone inherits two copies of a gene -- one is 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.
On the other hand, an individual who inherits two dominant copies of an allele will always express the trait. This is considered homozygous dominant. Dominant alleles are usually represented by, you guessed it, capital letters, i.e., a person with two dominant alleles, DD, for the trait of dimpled chin will definitely have a dimple in their chin.
So, if an individual has the genotype of Dd, this means they inherited one dominant and one recessive allele. This person would also be what is known as heterozygous for the trait and they will always express it. The rationale is that dominant alleles are precisely that -- dominant. Even inherited with a recessive allele, a dominant trait will without question be expressed.
Another intriguing facet of recessive traits is that they are more consequential than merely being masked. In some instances, receiving two copies of a recessive allele could indicate that a person will inherit a certain genetic disorder. A few commonly known examples of recessive inherited diseases are Tay Sachs, Sickle Cell Anemia, 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 distinctive inherited trait that is controlled by multiple alleles. Known as the ABO blood group, the three alleles of A, B, and O can present four different phenotypes from six genotypes. A and B are forever dominant to O in the ABO blood group.
In addition, A and B are codominant; this means if inherited together, both alleles will be expressed. Like any other inherited trait, only one allele will be donated from each parent. Possible combinations are AA, AO, BB, BO, AB, and OO. Resulting phenotypes are type A blood for AA and AO genotypes, type B blood for BB and BO genotypes, type AB blood for the AB genotype, and type O blood for the OO genotype. - 16492
The work of Gregor Mendel established fundamental rules for patterns of inheritance. The principles of genotypes and phenotypes must first be understood before mastering Mendel's rules. Although unfamiliar, these terms have a simple explanation.
A phenotype is the physical manifestation of a gene. A dimpled or cleft chin is an example of an inherited trait. Your phenotype is established by whether you have a dimple in your chin. In other words, you express the trait if you have a dimpled chin. In addition, this means the trait is dominant. A hidden trait, for example no dimpled chin, is known as recessive.
Conversely, a genotype is the full genetic information of an individual. So this means a genotype represents both of copies of the gene for a particular trait. Remember, everyone inherits two copies of a gene -- one is 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.
On the other hand, an individual who inherits two dominant copies of an allele will always express the trait. This is considered homozygous dominant. Dominant alleles are usually represented by, you guessed it, capital letters, i.e., a person with two dominant alleles, DD, for the trait of dimpled chin will definitely have a dimple in their chin.
So, if an individual has the genotype of Dd, this means they inherited one dominant and one recessive allele. This person would also be what is known as heterozygous for the trait and they will always express it. The rationale is that dominant alleles are precisely that -- dominant. Even inherited with a recessive allele, a dominant trait will without question be expressed.
Another intriguing facet of recessive traits is that they are more consequential than merely being masked. In some instances, receiving two copies of a recessive allele could indicate that a person will inherit a certain genetic disorder. A few commonly known examples of recessive inherited diseases are Tay Sachs, Sickle Cell Anemia, 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 distinctive inherited trait that is controlled by multiple alleles. Known as the ABO blood group, the three alleles of A, B, and O can present four different phenotypes from six genotypes. A and B are forever dominant to O in the ABO blood group.
In addition, A and B are codominant; this means if inherited together, both alleles will be expressed. Like any other inherited trait, only one allele will be donated from each parent. Possible combinations are AA, AO, BB, BO, AB, and OO. Resulting phenotypes are type A blood for AA and AO genotypes, type B blood for BB and BO genotypes, type AB blood for the AB genotype, and type O blood for the OO genotype. - 16492
About the Author:
RJ Sullivan manages several successful online businesses and is a distinguished editor and writer. Ms. Sullivan also writes for In the Gno, a blog devoted to presenting the science of genetics in an interesting and easy-to-understand manner. Visit her blog to learn more about mendelian genetics or blood types.
