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.
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.
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.
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 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 examples are known as autosomal disorders, or diseases linked to the 22 pairs of chromosomes that do not determine gender. Also interesting is that there are dominant inherited disorders which are highly lethal and X- or Y-linked disorders related to mutations in genes located on our sex-determining 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.
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.
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.
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.
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.
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 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 examples are known as autosomal disorders, or diseases linked to the 22 pairs of chromosomes that do not determine gender. Also interesting is that there are dominant inherited disorders which are highly lethal and X- or Y-linked disorders related to mutations in genes located on our sex-determining 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.
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.
About the Author:
RJ Sullivan manages several profitable online businesses and is a distinguished editor and writer. Ms. Sullivan also writes for In the Gno, a blog dedicated 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.
Posts
No comments:
Post a Comment