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 discoveries established basic rules for genetic principles and inheritance patterns. Understanding the concepts of genotypes and phenotypes is necessary to master Mendelian rules. Though these terms may be unfamiliar, each has 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.
On the other hand, a genotype is an individual's actual genetic information, whether hidden or expressed. In other words, a genotype indicates both allelic copies of the trait. Don't forget, everyone gets two copies of a gene -- one comes from each parent.
Dominance rules in patterns of inheritance are pretty straightforward. If an individual inherits two recessive alleles, the trait will always be hidden or masked. This individual would be considered a recessive homozygote.
Recessive alleles are usually written with lowercase letters. So, if we say that the lowercase letter d represents the trait for dimpled chin, then someone who inherits two recessive alleles, one from each parent, has the genotype of dd. Again, this person is said to be homozygous recessive.
Accordingly, if a person receives two copies of a dominant allele, the trait will always be expressed. The expression of two dominant alleles is termed homozygous dominant. Dominant alleles are typically indicated by, you guessed it, capital letters; thus, an individual who has two dominant alleles, DD, for the dimpled chin trait will absolutely 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 interesting point on recessive alleles and traits is that they are more significant than merely being hidden. In some cases, two copies of a recessive allele can mean that a person will inherit a genetic disease. Some commonly known recessive inherited diseases are Cystic Fibrosis, Sickle Cell Anemia, and Tay Sachs.
These are examples of autosomal disorders, which are diseases that are linked to the 22 pairs of chromosomes that do not determine our gender. Interestingly enough, there are also dominant inherited disorders which are quite lethal and sex-linked disorders that have to do with mutations in the genes located on our X or 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. - 16752
Mendel's discoveries established basic rules for genetic principles and inheritance patterns. Understanding the concepts of genotypes and phenotypes is necessary to master Mendelian rules. Though these terms may be unfamiliar, each has 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.
On the other hand, a genotype is an individual's actual genetic information, whether hidden or expressed. In other words, a genotype indicates both allelic copies of the trait. Don't forget, everyone gets two copies of a gene -- one comes from each parent.
Dominance rules in patterns of inheritance are pretty straightforward. If an individual inherits two recessive alleles, the trait will always be hidden or masked. This individual would be considered a recessive homozygote.
Recessive alleles are usually written with lowercase letters. So, if we say that the lowercase letter d represents the trait for dimpled chin, then someone who inherits two recessive alleles, one from each parent, has the genotype of dd. Again, this person is said to be homozygous recessive.
Accordingly, if a person receives two copies of a dominant allele, the trait will always be expressed. The expression of two dominant alleles is termed homozygous dominant. Dominant alleles are typically indicated by, you guessed it, capital letters; thus, an individual who has two dominant alleles, DD, for the dimpled chin trait will absolutely 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 interesting point on recessive alleles and traits is that they are more significant than merely being hidden. In some cases, two copies of a recessive allele can mean that a person will inherit a genetic disease. Some commonly known recessive inherited diseases are Cystic Fibrosis, Sickle Cell Anemia, and Tay Sachs.
These are examples of autosomal disorders, which are diseases that are linked to the 22 pairs of chromosomes that do not determine our gender. Interestingly enough, there are also dominant inherited disorders which are quite lethal and sex-linked disorders that have to do with mutations in the genes located on our X or 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. - 16752
About the Author:
RJ Sullivan manages several profitable home-based businesses and is an accomplished editor and writer. Ms. Sullivan also writes for In the Gno, a blog dedicated 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.
